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another name for the primary visual cortex is
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"docid": "D312959",
"title": "Visual cortex",
"text": "From Wikipedia, the free encyclopedianavigation search Visual cortex View of the brain from behind. Red = Brodmann area 17 (primary visual cortex); orange = area 18; yellow = area 19Brain shown from the side, facing left. Above: view from outside, below: cut through the middle. Orange = Brodmann area 17 (primary visual cortex)Details Identifiers Latin Cortex visualis Me SH D014793Neuro Lex ID nlx 143552FMA 242644Anatomical terms of neuroanatomy edit on Wikidata The visual cortex of the brain is a part of the cerebral cortex that processes visual information. It is located in the occipital lobe in the back of the head. Visual information coming from the eye goes through the lateral geniculate nucleus in the thalamus and then reaches the visual cortex. The part of the visual cortex that receives the sensory inputs from the thalamus is the primary visual cortex, also known as visual area 1 (V1), and the striate cortex. The extrastriate areas consist of visual areas 2 (V2), 3 (V3), 4 (V4), and 5 (V5). 1 Both hemispheres of the brain contain a visual cortex; the visual cortex in the left hemisphere receives signals from the right visual field, and the visual cortex in the right hemisphere receives signals from the left visual field. Contents hide 1 Introduction2 Psychological model of the neural processing of visual information2.1 Ventral-dorsal model3 Primary visual cortex (V1)3.1 Function4 V25 Third visual cortex, including area V36 V47 Middle temporal visual area (V5)7.1 Connections7.2 Function7.3 Functional organization8 V68.1 Properties8.2 Pathways9 See also10 References11 External links Introduction edit The primary visual cortex (V1) is located in and around the calcarine fissure in the occipital lobe. Each hemisphere's V1 receives information directly from its ipsilateral lateral geniculate nucleus that receives signals from the contralateral visual hemifield. Neurons in the visual cortex fire action potentials when visual stimuli appear within their receptive field. By definition, the receptive field is the region within the entire visual field that elicits an action potential. But, for any given neuron, it may respond best to a subset of stimuli within its receptive field. This property is called neuronal tuning. In the earlier visual areas, neurons have simpler tuning. For example, a neuron in V1 may fire to any vertical stimulus in its receptive field. In the higher visual areas, neurons have complex tuning. For example, in the inferior temporal cortex (IT), a neuron may fire only when a certain face appears in its receptive field. The visual cortex receives its blood supply primarily from the calcarine branch of the posterior cerebral artery. Psychological model of the neural processing of visual information edit Main article: Two-streams hypothesis Ventral-dorsal model edit The dorsal stream (green) and ventral stream (purple) are shown. They originate from primary visual cortex. V1 transmits information to two primary pathways, called the ventral stream and the dorsal stream. 2 The ventral stream begins with V1, goes through visual area V2, then through visual area V4, and to the inferior temporal cortex (IT cortex). The ventral stream, sometimes called the \"What Pathway\", is associated with form recognition and object representation. It is also associated with storage of long-term memory. The dorsal stream begins with V1, goes through Visual area V2, then to the dorsomedial area (DM/ V6) and Visual area MT (middle temporal/ V5) and to the posterior parietal cortex. The dorsal stream, sometimes called the \"Where Pathway\" or \"How Pathway\", is associated with motion, representation of object locations, and control of the eyes and arms, especially when visual information is used to guide saccades or reaching. The what vs. where account of the ventral/dorsal pathways was first described by Ungerleider and Mishkin. 3 More recently, Goodale and Milner extended these ideas and suggested that the ventral stream is critical for visual perception whereas the dorsal stream mediates the visual control of skilled actions. 4 It has been shown that visual illusions such as the Ebbinghaus illusion distort judgements of a perceptual nature, but when the subject responds with an action, such as grasping, no distortion occurs. 5 Work such as the one from Scharnowski and Gegenfurtner 6 suggests that both the action and perception systems are equally fooled by such illusions. Other studies, however, provide strong support for the idea that skilled actions such as grasping are not affected by pictorial illusions 7 8 and suggest that the action/perception dissociation is a useful way to characterize the functional division of labor between the dorsal and ventral visual pathways in the cerebral cortex. 9 Primary visual cortex (V1) edit This section needs additional citations for verification. Please help improve this article by adding citations to reliable sources. Unsourced material may be challenged and removed. (November 2016) ( Learn how and when to remove this template message)Micrograph showing the visual cortex (pink). The pia mater and arachnoid mater including blood vessels are seen at the top of the image. Subcortical white matter (blue) is seen at the bottom of the image. HE-LFB stain. The primary visual cortex is the most studied visual area in the brain. In mammals, it is located in the posterior pole of the occipital lobe and is the simplest, earliest cortical visual area. It is highly specialized for processing information about static and moving objects and is excellent in pattern recognition. clarification needed The functionally defined primary visual cortex is approximately equivalent to the anatomically defined striate cortex. clarification needed The name \"striate cortex\" is derived from the line of Gennari, a distinctive stripe visible to the naked eye 10 that represents myelinated axons from the lateral geniculate body terminating in layer 4 of the gray matter. The primary visual cortex is divided into six functionally distinct layers, labeled 1 to 6. Layer 4, which receives most visual input from the lateral geniculate nucleus (LGN), is further divided into 4 layers, labelled 4A, 4B, 4C , and 4C . Sublamina 4C clarification needed receives mostly magnocellular input from the LGN, while layer 4C receives input from parvocellular pathways. The average number of neurons in the adult human primary visual cortex in each hemisphere has been estimated at around 140 million. 11 Function edit relevant? discuss This article may be too technical for most readers to understand. Please help improve it to make it understandable to non-experts, without removing the technical details. (September 2016) ( Learn how and when to remove this template message)V1 has a very well-defined map of the spatial information in vision. For example, in humans, the upper bank of the calcarine sulcus responds strongly to the lower half of visual field (below the center), and the lower bank of the calcarine to the upper half of visual field. In concept, this retinotopic mapping is a transformation of the visual image from retina to V1. The correspondence between a given location in V1 and in the subjective visual field is very precise: even the blind spots are mapped into V1. In terms of evolution, this correspondence is very basic and found in most animals that possess a V1. In humans and animals with a fovea in the retina, a large portion of V1 is mapped to the small, central portion of visual field, a phenomenon known as cortical magnification. 12 Perhaps for the purpose of accurate spatial encoding, neurons in V1 have the smallest receptive field size of any visual cortex microscopic regions. The tuning properties of V1 neurons (what the neurons respond to) differ greatly over time. Early in time (40 ms and further) individual V1 neurons have strong tuning to a small set of stimuli. That is, the neuronal responses can discriminate small changes in visual orientations, spatial frequencies and colors. Furthermore, individual V1 neurons in human and animals with binocular vision have ocular dominance, namely tuning to one of the two eyes. In V1, and primary sensory cortex in general, neurons with similar tuning properties tend to cluster together as cortical columns. David Hubel and Torsten Wiesel proposed the classic ice-cube organization model of cortical columns for two tuning properties: ocular dominance and orientation. However, this model cannot accommodate the color, spatial frequency and many other features to which neurons are tuned citation needed . The exact organization of all these cortical columns within V1 remains a hot topic of current research. The mathematical modeling of this function has been compared to Gabor transforms. Later in time (after 100 ms), neurons in V1 are also sensitive to the more global organisation of the scene (Lamme & Roelfsema, 2000). 13 These response properties probably stem from recurrent feedback processing (the influence of higher-tier cortical areas on lower-tier cortical areas) and lateral connections from pyramidal neurons (Hupe et al. 1998). While feedforward connections are mainly driving, feedback connections are mostly modulatory in their effects (Angelucci et al., 2003; Hupe et al., 2001). Evidence shows that feedback originating in higher-level areas such as V4, IT, or MT, with bigger and more complex receptive fields, can modify and shape V1 responses, accounting for contextual or extra-classical receptive field effects (Guo et al., 2007; Huang et al., 2007; Sillito et al., 2006). The visual information relayed to V1 is not coded in terms of spatial (or optical) imagery but rather are better described as edge detection. As an example, for an image comprising half side black and half side white, the dividing line between black and white has strongest local contrast (that is, edge detection) and is encoded, while few neurons code the brightness information (black or white per se). As information is further relayed to subsequent visual areas, it is coded as increasingly non-local frequency/phase signals. Note that, at these early stages of cortical visual processing, spatial location of visual information is well preserved amid the local contrast encoding (edge detection). Axiomatically clarification needed determined functional models of simple cells in V1 have been determined by Lindeberg 14 15 in terms of directional derivatives clarification needed of affine Gaussian kernels clarification needed over the spatial domain clarification needed in combination with temporal derivatives clarification needed of either non-causal or time-causal scale-space kernels clarification needed over the temporal domain (see axiomatic theory of receptive fields ). Specifically, it has been shown that this theory both leads to predictions about receptive fields with good qualitative agreement with the biological receptive field measurements performed by De Angelis et al. 16 17 and guarantees good theoretical properties of the mathematical receptive field model, including covariance and invariance properties under natural image transformations. 18 relevant? discuss Differences in size of V1 also seem to have an effect on the perception of illusions. 19 V2 edit Visual area V2, or secondary visual cortex, also called prestriate cortex, 20 is the second major area in the visual cortex, and the first region within the visual association area. It receives strong feedforward connections from V1 (direct and via the pulvinar) and sends strong connections to V3, V4, and V5. It also sends strong feedback connections to V1. In terms of anatomy, V2 is split into four quadrants, a dorsal and ventral representation in the left and the right hemispheres. Together, these four regions provide a complete map of the visual world. V2 has many properties in common with V1: Cells are tuned to simple properties such as orientation, spatial frequency, and colour. The responses of many V2 neurons are also modulated by more complex properties, such as the orientation of illusory contours, 21 22 binocular disparity, 23 and whether the stimulus is part of the figure or the ground. 24 25 Recent research has shown that V2 cells show a small amount of attentional modulation (more than V1, less than V4), are tuned for moderately complex patterns, and may be driven by multiple orientations at different subregions within a single receptive field. It is argued that the entire ventral visual-to-hippocampal stream is important for visual memory. 26 This theory, unlike the dominant one, predicts that object-recognition memory (ORM) alterations could result from the manipulation in V2, an area that is highly interconnected within the ventral stream of visual cortices. In the monkey brain, this area receives strong feedforward connections from the primary visual cortex (V1) and sends strong projections to other secondary visual cortices (V3, V4, and V5). 27 28 Most of the neurons of this area are tuned to simple visual characteristics such as orientation, spatial frequency, size, color, and shape. 22 29 30 Anatomical studies implicate layer 3 of area V2 in visual-information processing. In contrast to layer 3, layer 6 of the visual cortex is composed of many types of neurons, and their response to visual stimuli is more complex. In a recent study, the Layer 6 cells of the V2 cortex were found to play a very important role in the storage of Object Recognition Memory as well as the conversion of short-term object memories into long-term memories. 31 Third visual cortex, including area V3 edit The term third visual complex refers to the region of cortex located immediately in front of V2, which includes the region named visual area V3 in humans. The \"complex\" nomenclature is justified by the fact that some controversy still exists regarding the exact extent of area V3, with some researchers proposing that the cortex located in front of V2 may include two or three functional subdivisions. For example, David Van Essen and others (1986) have proposed the existence of a \"dorsal V3\" in the upper part of the cerebral hemisphere, which is distinct from the \"ventral V3\" (or ventral posterior area, VP) located in the lower part of the brain. Dorsal and ventral V3 have distinct connections with other parts of the brain, appear different in sections stained with a variety of methods, and contain neurons that respond to different combinations of visual stimulus (for example, colour-selective neurons are more common in the ventral V3). Additional subdivisions, including V3A and V3B have also been reported in humans. These subdivisions are located near dorsal V3, but do not adjoin V2. Dorsal V3 is normally considered to be part of the dorsal stream, receiving inputs from V2 and from the primary visual area and projecting to the posterior parietal cortex. It may be anatomically located in Brodmann area 19. Braddick using f MRI has suggested that area V3/V3A may play a role in the processing of global motion 32 Other studies prefer to consider dorsal V3 as part of a larger area, named the dorsomedial area (DM), which contains a representation of the entire visual field. Neurons in area DM respond to coherent motion of large patterns covering extensive portions of the visual field (Lui and collaborators, 2006). Ventral V3 (VP), has much weaker connections from the primary visual area, and stronger connections with the inferior temporal cortex. While earlier studies proposed that VP contained a representation of only the upper part of the visual field (above the point of fixation), more recent work indicates that this area is more extensive than previously appreciated, and like other visual areas it may contain a complete visual representation. The revised, more extensive VP is referred to as the ventrolateral posterior area (VLP) by Rosa and Tweedale. 33 V4 edit See also: Color center Visual area V4 is one of the visual areas in the extrastriate visual cortex. In macaques, it is located anterior to V2 and posterior to posterior inferotemporal area (PIT). It comprises at least four regions (left and right V4d, left and right V4v), and some groups report that it contains rostral and caudal subdivisions as well. It is unknown whether the human V4 is as expansive as that of the macaque homologue which is a subject of debate. 34 V4 is the third cortical area in the ventral stream, receiving strong feedforward input from V2 and sending strong connections to the PIT. It also receives direct input from V1, especially for central space. In addition, it has weaker connections to V5 and dorsal prelunate gyrus (DP). V4 is the first area in the ventral stream to show strong attentional modulation. Most studies indicate that selective attention can change firing rates in V4 by about 20%. A seminal paper by Moran and Desimone characterizing these effects was the first paper to find attention effects anywhere in the visual cortex. 35 Like V2, V4 is tuned for orientation, spatial frequency, and color. Unlike V2, V4 is tuned for object features of intermediate complexity, like simple geometric shapes, although no one has developed a full parametric description of the tuning space for V4. Visual area V4 is not tuned for complex objects such as faces, as areas in the inferotemporal cortex are. The firing properties of V4 were first described by Semir Zeki in the late 1970s, who also named the area. Before that, V4 was known by its anatomical description, the prelunate gyrus. Originally, Zeki argued that the purpose of V4 was to process color information. Work in the early 1980s proved that V4 was as directly involved in form recognition as earlier cortical areas. citation needed This research supported the two-streams hypothesis, first presented by Ungerleider and Mishkin in 1982. Recent work has shown that V4 exhibits long-term plasticity, 36 encodes stimulus salience, is gated by signals coming from the frontal eye fields, 37 and shows changes in the spatial profile of its receptive fields with attention. citation needed Middle temporal visual area (V5) edit The middle temporal visual area ( MT or V5) is a region of extrastriate visual cortex. In several species of both New World monkeys and Old World monkeys the MT area contains a high concentration of direction-selective neurons. 38 The MT in primates is thought to play a major role in the perception of motion, the integration of local motion signals into global percepts, and the guidance of some eye movements. 38 Connections edit MT is connected to a wide array of cortical and subcortical brain areas. Its input comes from visual cortical areas V1, V2 and dorsal V3 ( dorsomedial area ), 39 40 the koniocellular regions of the LGN, 41 and the inferior pulvinar. 42 The pattern of projections to MT changes somewhat between the representations of the foveal and peripheral visual fields, with the latter receiving inputs from areas located in the midline cortex and retrosplenial region. 43 A standard view is that V1 provides the \"most important\" input to MT. 38 Nonetheless, several studies have demonstrated that neurons in MT are capable of responding to visual information, often in a direction-selective manner, even after V1 has been destroyed or inactivated. 44 Moreover, research by Semir Zeki and collaborators has suggested that certain types of visual information may reach MT before it even reaches V1. MT sends its major output to areas located in the cortex immediately surrounding it, including areas FST, MST, and V4t (middle temporal crescent). Other projections of MT target the eye movement-related areas of the frontal and parietal lobes (frontal eye field and lateral intraparietal area). Function edit The first studies of the electrophysiological properties of neurons in MT showed that a large portion of the cells are tuned to the speed and direction of moving visual stimuli. 45 46 Lesion studies have also supported the role of MT in motion perception and eye movements. 47 Neuropsychological studies of a patient unable to see motion, seeing the world in a series of static 'frames' instead, suggested that V5 in the primate is homologous to MT in the human. 48 49 However, since neurons in V1 are also tuned to the direction and speed of motion, these early results left open the question of precisely what MT could do that V1 could not. Much work has been carried out on this region, as it appears to integrate local visual motion signals into the global motion of complex objects. 50 For example, lesion to the V5 leads to deficits in perceiving motion and processing of complex stimuli. It contains many neurons selective for the motion of complex visual features (line ends, corners). Microstimulation of a neuron located in the V5 affects the perception of motion. For example, if one finds a neuron with preference for upward motion in a monkey's V5 and stimulates it with an electrode, then the monkey becomes more likely to report 'upward' motion when presented with stimuli containing 'left' and 'right' as well as 'upward' components. 51 There is still much controversy over the exact form of the computations carried out in area MT 52 and some research suggests that feature motion is in fact already available at lower levels of the visual system such as V1. 53 54 Functional organization edit MT was shown to be organized in direction columns. 55 De Angelis argued that MT neurons were also organized based on their tuning for binocular disparity. 56 V6 edit The dorsomedial area (DM) also known as V6, appears to respond to visual stimuli associated with self-motion 57 and wide-field stimulation. 58 V6, is a subdivision of the visual cortex of primates first described by John Allman and Jon Kaas in 1975. 59 V6 is located in the dorsal part of the extrastriate cortex, near the deep groove through the centre of the brain ( medial longitudinal fissure ), and typically also includes portions of the medial cortex, such as the parieto-occipital sulcus. citation needed DM contains a topographically organized representation of the entire field of vision. citation needed There are similarities between the visual area V5 and V6 of the common marmoset. Both areas receive direct connections from the primary visual cortex. citation needed And both have a high myelin content, a characteristic that is usually present in brain structures involved in fast transmission of information. citation needed For many years, it was considered that DM only existed in New World monkeys. citation needed However, more recent research has suggested that DM also exists in Old World monkeys and perhaps humans. citation needed V6 is also sometimes referred to as the parieto-occipital area (PO), although the correspondence is not exact. 60 61 Properties edit Neurons in area DM/V6 of night monkeys and common marmosets have unique response properties, including an extremely sharp selectivity for the orientation of visual contours, and preference for long, uninterrupted lines covering large parts of the visual field. 62 63 However, in comparison with area MT, a much smaller proportion of DM cells shows selectivity for the direction of motion of visual patterns. 64 Another notable difference with area MT is that cells in DM are attuned to low spatial frequency components of an image, and respond poorly to the motion of textured patterns such as a field of random dots. 64 These response properties suggest that DM and MT may work in parallel, with the former analyzing self-motion relative to the environment, and the latter analyzing the motion of individual objects relative to the background. 64 Recently, an area responsive to wide-angle flow fields has been identified in the human and is thought to be a homologue of macaque area V6. 65 Pathways edit The connections and response properties of cells in DM/ V6 suggest that this area is a key node in a subset of the ' dorsal stream ', referred to by some as the 'dorsomedial pathway'. citation needed This pathway is likely to be important for the control of skeletomotor activity, including postural reactions and reaching movements towards objects 61 The main 'feedforward' connection of DM is to the cortex immediately rostral to it, in the interface between the occipital and parietal lobes (V6A). citation needed This region has, in turn, relatively direct connections with the regions of the frontal lobe that control arm movements, including the premotor cortex. citation needed See also edit Neuroscience portal Cortical area Cortical blindness Feature integration theory List of regions in the human brain Retinotopy Visual processing Visual feature array Complex cell References edit Mather, George. \"The Visual Cortex\". 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Brain Res. 35 (2): 528 32. doi: 10.1016/0006-8993 (71)90494-X. PMID 5002708.. Maunsell J, Van Essen D (1983). \"Functional properties of neurons in middle temporal visual area of the macaque monkey. I. Selectivity for stimulus direction, speed, and orientation\". J Neurophysiol. 49 (5): 1127 47. PMID 6864242. Dursteler M. R.; Wurtz R. H.; Newsome W. T. (1987). \"Directional pursuit deficits following lesions of the foveal representation within the superior temporal sulcus of the macaque monkey\". Journal of Neurophysiology. 57 (5): 1262 87. PMID 3585468. Hess R. H.; Baker C. L.; Zihl J. (1989). \"The 'motion-blind' patient: low-level spatial and temporal filters\". Journal of Neuroscience. 9 (5): 1628 40. PMID 2723744. Baker C. L. Jr; Hess R. F; Zihl J. (1991). \"Residual motion perception in a 'motion-blind' patient, assessed with limited-lifetime random dot stimuli\". Journal of Neuroscience. 11 (2): 454 61. PMID 1992012. Movshon, J. A., Adelson, E. H., Gizzi, M. S., & Newsome, W. T. (1985). The analysis of moving visual patterns. In: C. Chagas, R. Gattass, & C. Gross (Eds. ), Pattern recognition mechanisms (pp. 117-151), Rome: Vatican Press. Britten K. H.; van Wezel R. J. (1998). \"Electrical microstimulation of cortical area MST biases heading perception in monkeys\". Nat. Neurosci. 1 (1): 59 63. doi: 10.1038/259. PMID 10195110. Wilson, H. R.; Ferrera, V. P.; Yo, C. (1992). \"A psychophysically motivated model for two-dimensional motion perception\". Vis Neurosci. 9 (1): 79 97. doi: 10.1017/s0952523800006386. Tinsley, C. J., Webb, B. S., Barraclough, N. E., Vincent, C. J., Parker, A., & Derrington, A. M. (2003). \"The nature of V1 neural responses to 2D moving patterns depends on receptive-field structure in the marmoset monkey\". J Neurophysiol. 90 (2): 930 7. doi: 10.1152/jn.00708.2002. PMID 12711710. Pack C. C.; Born R. T.; Livingstone M. S. (2003). \"Two-dimensional substructure of stereo and motion interactions in macaque visual cortex\". Neuron. 37 (3): 525 35. doi: 10.1016/s0896-6273 (02)01187-x. PMID 12575958. Albright T (1984). \"Direction and orientation selectivity of neurons in visual area MT of the macaque\". J Neurophysiol. 52 (6): 1106 30. PMID 6520628. De Angelis G, Newsome W (1999). \"Organization of disparity-selective neurons in macaque area MT\". J Neurosci. 19 (4): 1398 415. PMID 9952417. Cardin, V; Smith, AT (2010). \"Sensitivity of human visual and vestibular cortical regions to stereoscopic depth gradients associated with self-motion\". Cerebral Cortex. 20 (8): 1964 73. doi: 10.1093/cercor/bhp268. Pitzalis et alt. (2006). \"Wide-Field Retinotopy Defines Human Cortical Visual Area V6\". The Journal of Neuroscience. 26 (30): 7962 73. doi: 10.1523/jneurosci.0178-06.2006. PMID 16870741. Allman JM, Kaas JH (1975). \"The dorsomedial cortical visual area: a third tier area in the occipital lobe of the owl monkey (Aotus trivirgatus)\". Brain Res. 100 (3): 473 487. doi: 10.1016/0006-8993 (75)90153-5. Galletti C, et al. (2005). et al 2005.pdf \"The relationship between V6 and PO in macaque extrastriate cortex\"Check url= value ( help) (PDF). Eur J Neurosci. 21: 959 970. doi: 10.1111/j.1460-9568.2005.03911.x. a b Galletti C, et al. (2003). \"Role of the medial parieto-occipital cortex in the control of reaching and grasping movements\". Exp Brain Res. 153: 158 170. doi: 10.1007/s00221-003-1589-z. Baker JF, et al. (1981). \"Visual response properties of neurons in four extrastriate visual areas of the owl monkey (Aotus trivirgatus): a quantitative comparison of medial, dorsomedial, dorsolateral, and middle temporal areas\". J Neurophysiol. 45: 397 416. Lui LL, et al. (2006). \"Functional response properties of neurons in the dorsomedial visual area of New World monkeys (Callithrix jacchus)\". Cereb Cortex. 16 (2): 162 177. doi: 10.1093/cercor/bhi094. a b c http://www.fmritools.com/kdb/grey-matter/occipital-lobe/calcarine-visual-cortex/index.html Pitzalis, S., Sereno, M. I., Committeri, G., Fattori, P., Galati, G., Patria, F., & Galletti, C. (2010). \"Human v6: The medial motion area\". Cereb Cortex. 20 (2): 411 424. doi: 10.1093/cercor/bhp112. External links edit Wikimedia Commons has media related to Visual cortex. The Primary Visual Cortex by Matthew Schmolesky at University of Utah Architecture of the Visual Cortex, by David Hubel at Harvard Universityancil-415 at Neuro Names - striate area 17ancil-699 at Neuro Names - Brodmann area 17 in guenon Stained brain slice images which include the \"visual%20cortex\" at the Brain Maps project Simulator for computational modeling of visual cortex maps at topographica.org show v t e Anatomy of the cerebral cortex of the human brain show v t e Optical illusions Categories: Visual cortex Visual perception "
}
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[
{
"docid": "D312959",
"title": "What is the structure of the Visual Cortex?",
"text": "What is the structure of the Visual Cortex? Print Email Save Image Credit: pnas.org The role of eyes in human life is amazing. Eyes make us percieve the world around us better and we get to see all the beautiful and important things necessary for our survival. They make our human life colorful. One of the major components of the human eyes is Visual cortex. Imagine seeing things upside down. Well, this is where the Visual cortex helps us out. It is responsible for sorting these images and making them appear in the right direction to our eyes. The Visual cortex is a component of the cerebral cortex that receives and processes the sensory nerve impulses from the eyes. The cerebral cortex is a layer of neural tissue that participates actively in the reminiscence, concentration, consciousness, thinking process and language processes. The cerebral cortex is about 2 4 mm wide in human beings. There is one Visual cortex in each hemisphere of the brain. The Visual cortex that is present in the left hemisphere of the brain gets signals from the right visual area and vice versa. Visual Cortex is found in the occipital lobe at the rear of the brain. The occipital lobe is the part of the brain that converts the nerve impulses that are received from the eyes into images. Content What does Visual cortex encompass? What is the task of Visual cortex? What is the importance of primary Visual cortex? How is the Visual cortex organized in primates? How is Visual cortex organized in humans? What does Visual cortex encompass? Generally, the Visual cortex encompasses the primary visual cortex and extra-striate visual cortical areas (visual area V2, visual area V3, visual area V4 and visual area MT or V5). The extrastriate cortex is found in the occipital cortex section of the human brain that is found behind the primary visual cortex. The primary visual cortex structurally corresponds to Brodmann area 17 or BA17. Brodmann area is a division of the cerebral cortex that is classified based on the grouping of You do not have access to view this node. The extrastriate cortical areas are made up of Brodmann area 18 and Brodmann area 19. Both belong to the occipital cortex sections of the human brain. V1 has a unique diagram of the spatial data in the mental image. The visual area V5 is believed to perform a key function in the motion perception. The process of understanding the speed and pathway of the objects or entities is known as motion perception. V5 is also called visual area MT . What is the task of Visual cortex? In essence, the task of the Visual cortex is to illustrate a person about what he or she is viewing at that particular moment. Visual cortex receives the impulses that are conveyed to it from the eye. These impulses include what and how the image should appear. However, the image received by the Visual cortex will be upside-down. So, the job of Visual cortex is to flip it and make the image appear in the right direction. Generally, the Visual cortex is referred to as the mind's eye of a person, as it illustrates a person s memories or his or her mind's eye. What is the importance of primary Visual cortex? Primary Visual cortex is the major cortical visual region. The primary Visual cortex is found at the rear of the occipital lobe in the cerebral cortex. Even if one portion of the primary Visual cortex is damaged it can lead to cortical blindness. The obliteration of the Visual cortex in the right hemisphere may cause blindness in the left visual area. It is extremely focused in handling still and mobile objects and is exceptional in identifying the prototype. The V1 of each hemisphere gets the information easily from the 'ipsilateral lateral geniculate nucleus' which is the most important communicate hub for visual information it gets from the retina of the eye. Each V1 conveys the data to two major streams: Dorsal stream: Dorsal stream starts from V1 traverse the Visual region V2 and dorso medial area (also known as DM or V6 and Visual region V5) and finally reaches the posterior parietal cortex that plays a vital role in generating the movements that are expected. The dorsal stream is also called \"Where Pathway\" or \"How Pathway\" and is related to the You do not have access to view this node, depiction of positions of objects and also responsible for managing the movements of eyes and arms. Ventral stream: Ventral stream starts from V1, traverses the visual V2 area and visual V4 area and finally passes through the inferior temporal cortex. Inferior temporal cortex is one of the highest levels of the ventral stream of visual processing. It takes part in the depiction of intricate features of objects. It may also be concerned in face discernment. The ventral stream is also known as the \"What Pathway\" and plays a major role in the identification of shapes and depiction of an object. It is also involved in the storage of permanent memories in the brain. How is the Visual cortex organized in primates? Basically, the primate Visual cortex is organized into two isolated processing methods such as a ventral stream for entity vision and a dorsal stream for space vision. The facts from functional brain imaging in humans reveals that the object depictions are not restricted to the ventral pathway but can also be predicted in a number of regions in the dorsal corridor also. How is Visual cortex organized in humans? Measurement of retino topic organization within human cortex is explained by the 'functional magnetic resonance imaging (f MRI)' method. The technique relies mostly on a visual stimulus that produces a wandering wave of neural activity inside the retino topically organized visual regions. Scientists deliberated the f MRI signal produced by this stimulus in visual cortex and depicted the outcomes on the images. Scientists utilized different techniques to find out the visual regions and to calculate the spatial accuracy of f MRI. In particular, the scientists did the following: Determined the margins connecting a number of retinotopically organized visual regions in the back side of the occipital lobe. Deliberated the function involving the position of cortical area to visual field idiosyncrasy inside the V1 region. Restricted movement inside 1.1 mm of the Visual cortex. Determined the spatial resolution of the f MRI signal and discovered that signal amplitude drops to 60% at a spatial incidence of one full rotation per 9 mm of Visual cortex. External Referencesdash.harvard.edu : Cortexeverything2.com : Cortexprinceton.edu : Cortex Related Videos: "
},
{
"docid": "D312959",
"title": "What sulcus separates the primary motor cortex fron the primary sensory cortex?",
"text": "Answers.com Wiki Answers Categories Science Biology Human Anatomy and Physiology What sulcus separates the primary motor cortex fron the primary sensory cortex? Flag What sulcus separates the primary motor cortex fron the primary sensory cortex? Answered by The Wiki Answers Community Answers.com is making the world better one answer at a time. The central sulcus is a fold in the cerebral cortex of brains in vertebrates. Also called the central fissure, it was originally called the fissure of Rolando or the Rolandic fissure, after Luigi Rolando. The central sulcus is a prominent landmark of the brain, separating the parietal lobe from the frontal lobe and the primary motor cortex from the primary somatosensory cortex.2 people found this useful Was this answer useful? Yes Somewhat No What is the function of the primary visual cortex? Simply stated, it is the area of the occipital lobe in the back of the brain responsible for processing visual information into an image that the person sees. The visual assoc What is the difference between motor cortex and sensory cortex? The motor cortex is in the frontal lobe of the brain whilst thesensory cortex is in the parietal lobe. Another main difference isthat the motor cortex controls movements of fi What is the function of the Primary Motor Cortex? The primary motor cortex controls voluntary movements. Damage tothe primary cortex would impact the ability to control voluntarymovement. Damage to primary sensory cortex? Because the primary sensory area contains the visual, olfactory, taste, auditory, visceral, and the vestibular area, damage to it will make a human being an object without any Tabatha Keeler 5 Contributions Where does the neurons in the primary sensory cortex receive somatic information from? Most of the sensory information first goes through the thalamus. touch, pressure, pain, taste, and temperature receptors. Kelly Jameson 34,271 Contributions Where is the primary sensory cortex located? The primary sensory cortex (or primary somatosensory cortex) is part of the postcentral gyrus in the brain, which forms part of the parietal lobe. The main function of the pr Where is the primary motor cortex found? The primary motor cortex is located in the precentral gyrus of thethe frontal lobe of the cerebrum. What is the largest portion of the primary motor and sensory cortex devoted to?fingertips Tim Mullican 2,269 Contributions In which lobe of the brain is the primary motor cortex? The frontal lobe. Show me the answer 3 Contributions Is the primary motor cortex the surface of the precentral gyrus? Yes :)Which of the cerebral lobes is the primary motor cortex? Frontal. It lies just in front of the central sulcus. Tim Mullican 2,269 Contributions Where are the sensory and motor cortex located? The sensory cortex is located on the postcentral gyrus and the motor cortex is located on the precentral gyrus. Tim Mullican 2,269 Contributions Answered In Human Anatomy and Physiology What central lobe of the brain is the primary motor cortex? The primary motor cortex is located on the precentral gyrus which is part of the frontal lobe of the cerebrum. Sandhrt1 98 Contributions Answered In Human Anatomy and Physiology What contains the primary motor area of the cerebral cortex? Postcentral gyrus contains the primary motor area of the cerebralcortex. Answered In Human Anatomy and Physiology Is it true that information flows from the sensory receptors to the appropriate primary sensory cortex? Yes Steve Watkins 120 Contributions Answered In Human Anatomy and Physiology Are touch and pain from the primary sensory cortex? Fine touch is detected in the PSC but pain (or more accurately nocioception) is more complecated. Fast pain terminates in the thalamus Slow pain terminates in the lamina Amaroque 6,013 Contributions Answered In Human Anatomy and Physiology Is the primary motor cortex white matter or gray matter? All of the cerebral cortex is gray matter as it composed of neuronal cell bodies which are not insulated with myelin. "
},
{
"docid": "D312959",
"title": "Visual cortex",
"text": "Visual cortexnavigation search Brain: Visual cortex Brodmann area 17 (primary visual cortex) is shown in red in this image which also shows area 18 (orange) and 19 (yellow)Dorlands/Elsevier c 57/12261838The term visual cortex refers to the primary visual cortex (also known as striate cortex or V1) and extrastriate visual cortical areas such as V2, V3, V4, and V5. The primary visual cortex is anatomically equivalent to Brodmann area 17, or BA17. Introduction The primary visual cortex, V1, is the koniocortex (sensory type) located in and around the calcarine fissure in the occipital lobe. It receives information directly from the lateral geniculate nucleus . The dorsal stream (green) and ventral stream (purple) are shown. They originate from primary visual cortex. V1 transmits information to two primary pathways, called the dorsal stream and the ventral stream: The dorsal stream begins with V1, goes through Visual area V2, then to the dorsomedial area and Visual area MT (also known as V5) and to the posterior parietal cortex. The dorsal stream, sometimes called the \"Where Pathway\", is associated with motion, representation of object locations, and control of the eyes and arms, especially when visual information is used to guide saccades or reaching. 1 The ventral stream begins with V1, goes through Visual area V2, then through Visual area V4, and to the inferior temporal cortex. The ventral stream, sometimes called the \"What Pathway\", is associated with form recognition and object representation. It is also associated with storage of long-term memory. The dichotomy of the dorsal/ventral pathways (also called the \"where/what\" or \"action/perception\" streams) 1 was first defined by Ungerleider and Mishkin 2 and is still contentious among vision scientists and psychologists. It is probably an over-simplification of the true state of affairs in the visual cortex. It is based on the findings that visual illusions such as the Ebbinghaus illusion may distort judgements of a perceptual nature, but when the subject responds with an action, such as grasping, no distortion occurs. However, recent work 3 suggests that both the action and perception systems are equally fooled by such illusions. Neurons in the visual cortex fire action potentials when visual stimuli appear within their receptive field. By definition, the receptive field is the region within the entire visual field which elicits an action potential. But for any given neuron, it may respond to a subset of stimuli within its receptive field. This property is called tuning. In the earlier visual areas, neurons have simpler tuning. For example, a neuron in V1 may fire to any vertical stimulus in its receptive field. In the higher visual areas, neurons have complex tuning. For example, in the inferior temporal cortex (IT), a neuron may only fire when a certain face appears in its receptive field. The visual cortex receives its blood supply primarily from the calcarine branch of the posterior cerebral artery . Current research Research on the primary visual cortex can involve recording action potentials from electrodes within the brain of cats, ferrets, rats, mice, or monkeys, or through recording intrinsic optical signals from animals or f MRI signals from human and monkey V1. One recent discovery concerning the human V1 is that signals measured by f MRI show very large attentional modulation. This result strongly contrasts with macaque physiology research showing very small changes (or no changes) in firing associated with attentional modulation. Research with the macaque monkey is usually performed by measuring spiking activity from single neurons. The neural basis of the f MRI signal on the other hand is mostly related to post synaptic potentiation (PSP). This difference therefore does not necessarily indicate a difference between macaque and human physiology. Other current work on V1 seeks to fully characterize its tuning properties, and to use it as a model area for the canonical cortical circuit. Lesions to primary visual cortex usually lead to a scotoma, or hole in the visual field. Interestingly, patients with scotomas are often able to make use of visual information presented to their scotomas, despite being unable to consciously perceive it. This phenomenon, called blindsight, is widely studied by scientists interested in the neural correlate of consciousness . Primary visual cortex (V1)The primary visual cortex is the best studied visual area in the brain. In all mammals studied, it is located in the posterior pole of the occipital cortex (the occipital cortex is responsible for processing visual stimuli). It is the simplest, earliest cortical visual area. It is highly specialized for processing information about static and moving objects and is excellent in pattern recognition. The functionally defined primary visual cortex is approximately equivalent to the anatomically defined striate cortex. The name \"striate cortex\" is derived from the stria of Gennari, a distinctive stripe visible to the naked eye that represents myelinated axons from the lateral geniculate body terminating in layer 4 of the gray matter . The primary visual cortex is divided into six functionally distinct layers, labelled 1 through 6. Layer 4, which receives most visual input from the lateral geniculate nucleus (LGN), is further divided into 4 layers, labelled 4A, 4B, 4C , and 4C . Sublamina 4C receives most magnocellular input from the LGN, while layer 4C receives input from parvocellular pathways . The average number of neurons in the adult human primary visual cortex, in each hemisphere, has been estimated at around 140 million (Leuba & Kraftsik, Anatomy and Embryology, 1994). Function V1 has a very well-defined map of the spatial information in vision. For example, in humans the upper bank of the calcarine sulcus responds strongly to the lower half of visual field (below the center), and the lower bank of the calcarine to the upper half of visual field. Conceptually, this retinotopy mapping is a transformation of the visual image from retina to V1. The correspondence between a given location in V1 and in the subjective visual field is very precise: even the blind spots are mapped into V1. Evolutionarily, this correspondence is very basic and found in most animals that possess a V1. In human and animals with a fovea in the retina, a large portion of V1 is mapped to the small, central portion of visual field, a phenomenon known as cortical magnification. Perhaps for the purpose of accurate spatial encoding, neurons in V1 have the smallest receptive field size of any visual cortex microscopic regions. The tuning properties of V1 neurons (what the neurons respond to) differ greatly over time. Early in time (40 ms and further) individual V1 neurons have strong tuning to a small set of stimuli. That is, the neuronal responses can discriminate small changes in visual orientations, spatial frequencies and colors. Furthermore, individual V1 neurons in human and animals with binocular vision have ocular dominance, namely tuning to one of the two eyes. In V1, and primary sensory cortex in general, neurons with similar tuning properties tend to cluster together as cortical columns. David Hubel and Torsten Wiesel proposed the classic ice-cube organization model of cortical columns for two tuning properties: ocular dominance and orientation. However, this model cannot accommodate the color, spatial frequency and many other features to which neurons are tuned. The exact organization of all these cortical columns within V1 remains a hot topic of current research. Current consensus seems to be that early responses of V1 neurons consists of tiled sets of selective spatiotemporal filters. In the spatial domain, the functioning of V1 can be thought of as similar to many spatially local, complex Fourier transforms. Theoretically, these filters together can carry out neuronal processing of spatial frequency, orientation, motion, direction, speed (thus temporal frequency), and many other spatiotemporal features. Experiments of V1 neurons substantiate these theories, but also raise new questions. Later in time (after 100 ms) neurons in V1 are also sensitive to the more global organisation of the scene (Lamme & Roelfsema, 2000). These response properties probably stem from recurrent processing (the influence of higher-tier cortical areas on lower-tier cortical areas) and lateral connections from pyramidal neurons (Hupe et al 1998). The visual information relayed to V1 is not coded in terms of spatial (or optical) imagery, but rather as the local contrast. As an example, for an image comprising half side black and half side white, the divide line between black and white has strongest local contrast and is encoded, while few neurons code the brightness information (black or white per se). As information is further relayed to subsequent visual areas, it is coded as increasingly non-local frequency/phase signals. Importantly, at these early stages of cortical visual processing, spatial location of visual information is well preserved amid the local contrast encoding. V2Visual area V2, also called prestriate cortex, 4 is the second major area in the visual cortex, and the first region within the visual association area. It receives strong feedforward connections from V1 and sends strong connections to V3, V4, and V5. It also sends strong feedback connections to V1. Anatomically, V2 is split into four quadrants, a dorsal and ventral representation in the left and the right hemispheres. Together these four regions provide a complete map of the visual world. Functionally, V2 has many properties in common with V1. Cells are tuned to simple properties such as orientation, spatial frequency, and color. The responses of many V2 neurons are also modulated by more complex properties, such as the orientation of illusory contours and whether the stimulus is part of the figure or the ground (Qiu and von der Heydt, 2005). Recent research has shown that V2 cells show a small amount of attentional modulation (more than V1, less than V4), are tuned for moderately complex patterns, and may be driven by multiple orientations at different subregions within a single receptive field. Third visual complex, including area V3The term third visual complex refers to the region of cortex located immediately in front of V2, which includes the region named visual area V3 in humans. The \"complex\" nomenclature is justified by the fact that some controversy still exists regarding the exact extent of area V3, with some researchers proposing that the cortex located in front of V2 may include two or three functional subdivisions. For example, David Van Essen and others (1986) have proposed that the existence of a \"dorsal V3\" in the upper part of the cerebral hemisphere, which is distinct from the \"ventral V3\" (or ventral posterior area, VP) located in the lower part of the brain. Dorsal and ventral V3 have distinct connections with other parts of the brain, appear different in sections stained with a variety of methods, and contain neurons that respond to different combinations of visual stimulus (for example, colour-selective neurons are more common in the ventral V3). Additional subdivisions, including V3A and V3B have also been reported in humans. These subdivisions are located near dorsal V3, but do not adjoin V2. Dorsal V3 is normally considered to be part of the dorsal stream, receiving inputs from V2 and from the primary visual area and projecting to the posterior parietal cortex. It may be anatomically located in Brodmann area 19. Recent work with f MRI has suggested that area V3/V3A may play a role in the processing of global motion 5 Other studies prefer to consider dorsal V3 as part of a larger area, named the dorsomedial area (DM), which contains a representation of the entire visual field. Neurons in area DM respond to coherent motion of large patterns covering extensive portions of the visual field (Lui and collaborators, 2006). Ventral V3 (VP), has much weaker connections from the primary visual area, and stronger connections with the inferior temporal cortex. While earlier studies proposed that VP only contained a representation of the upper part of the visual field (above the point of fixation), more recent work indicates that this area is more extensive than previously appreciated, and like other visual areas it may contain a complete visual representation. The revised, more extensive VP is referred to as the ventrolateral posterior area (VLP) by Rosa and Tweedale. 6 V4Visual area V4 is one of the visual areas in the extrastriate visual cortex of the macaque monkey. It is located anterior to V2 and posterior to visual area PIT. It comprises at least four regions (left and right V4d, left and right V4v), and some groups report that it contains rostral and caudal subdivisions as well. It is unknown what the human homologue of V4 is, and this issue is currently the subject of much scrutiny. V4 is the third cortical area in the ventral stream, receiving strong feedforward input from V2 and sending strong connections to the posterior inferotemporal cortex (PIT). It also receives direct inputs from V1, especially for central space. In addition, it has weaker connections to V5 and visual area DP (the dorsal prelunate gyrus). V4 is the first area in the ventral stream to show strong attentional modulation. Most studies indicate that selective attention can change firing rates in V4 by about 20%. A seminal paper by Moran and Desimone characterizing these effects was the first paper to find attention effects anywhere in the visual cortex 1 . 7 Like V1, V4 is tuned for orientation, spatial frequency, and color. Unlike V1, V4 is tuned for object features of intermediate complexity, like simple geometric shapes, although no one has developed a full parametric description of the tuning space for V4. Visual area V4 is not tuned for complex objects such as faces, as areas in the inferotemporal cortex are. The firing properties of V4 were first described by Semir Zeki in the late 1970s, who also named the area. Before that, V4 was known by its anatomical description, the prelunate gyrus. Originally, Zeki argued that the purpose of V4 was to process color information. Work in the early 1980s proved that V4 was as directly involved in form recognition as earlier cortical areas. This research supported the Two Streams hypothesis, first presented by Ungerleider and Mishkin in 1982. Recent work has shown that V4 exhibits long-term plasticity, encodes stimulus salience, is gated by signals coming from the frontal eye fields, shows changes in the spatial profile of its receptive fields with attention. V5/MTVisual area V5, also known as visual area MT (middle temporal), is a region of extrastriate visual cortex that is thought to play a major role in the perception of motion, the integration of local motion signals into global percepts and the guidance of some eye movements. 8 Connections MT is connected to a wide array of cortical and subcortical brain areas. Its inputs include the visual cortical areas V1, V2, and dorsal V3 ( dorsomedial area ), 9 10 the koniocellular regions of the LGN, 11 and the inferior pulvinar. The pattern of projections to MT changes somewhat between the representations of the foveal and peripheral visual fields, with the latter receiving inputs from areas located in the midline cortex and retrosplenial region 12 A standard view is that V1 provides the \"most important\" input to MT. 8 Nonetheless, several studies have demonstrated that neurons in MT are capable of responding to visual information, often in a direction-selective manner, even after V1 has been destroyed or inactivated. 13 Moreover, research by Semir Zeki and collaborators has suggested that certain types of visual information may reach MT before it even reaches V1. MT sends its major outputs to areas located in the cortex immediately surrounding it, including areas FST, MST and V4t (middle temporal crescent). Other projections of MT target the eye movement-related areas of the frontal and parietal lobes (frontal eye field and lateral intraparietal area). Function The first studies of the electrophysiological properties of neurons in MT showed that a large portion of the cells were tuned to the speed and direction of moving visual stimuli 14 15 These results suggested that MT played a significant role in the processing of visual motion. Lesion studies have also supported the role of MT in motion perception and eye movements and neuropsychological studies of a patient who could not see motion, seeing the world in a series of static \"frames\" instead, suggested that MT in the primate is homologous to V5 in the human. 16 17 However, since neurons in V1 are also tuned to the direction and speed of motion, these early results left open the question of precisely what MT could do that V1 could not. Much work has been carried out on this region as it appears to integrate local visual motion signals into the global motion of complex objects. 18 For examples, lesion to the V5 lead to deficits in perceiving motion and processing of complex stimuli. It contains many neurons selective for the motion of complex visual features (line ends, corners). Microstimulation of a neuron located in the V5 affects the perception of motion. For example if one finds a neuron with preference for upward motion, and then we use an electrode to stimulate it, the monkey becomes more likely to report 'upward' motion. 19 There is still much controversy over the exact form of the computations carried out in area MT 20 and some research suggests that feature motion is in fact already available at lower levels of the visual system such as V1. 21 22 Functional organization MT was shown to be organized in direction columns. 23 De Angelis argued that MT neurons were also organized based on their tuning for binocular disparity. 24 References 1.0 1.1Goodale & Milner (1992). \"Separate pathways for perception and action.\". Trends in Neuroscience. 15: 20 25. doi: 10.1016/0166-2236 (92)90344-8. Ungerleider and Mishkin (1982). Ingle DJ, Goodale MA and Mansfield RJW, ed. Analysis of Visual Behavior. MIT Press. Franz VH, Scharnowski F, Gegenfurtner (2005). \"Illusion effects on grasping are temporally constant not dynamic.\". J Exp Psychol Hum Percept Perform. 31 (6): 1359 78. Gazzaniga, Ivry & Mangun: Cognitive neuroscience, 2002 Braddick, OJ, O'Brian, JMD; et al. (2001). \"Brain areas sensitive to visual motion.\". Perception. 30: 61 72. doi: 10.1068/p3048. Rosa MG, Tweedale R (2000) Visual areas in lateral and ventral extrastriate cortices of the marmoset monkey. J Comp Neurol 422:621-51. Moran & Desimone. Selective Attention Gates Visual Processing in the Extrastriate Cortex. Science 229 (4715), 1985. 8.0 8.1Born R, Bradley D. \"Structure and function of visual area MT.\". Annu Rev Neurosci. 28: 157 89. PMID 16022593. Felleman D, Van Essen D. \"Distributed hierarchical processing in the primate cerebral cortex.\". Cereb Cortex. 1 (1): 1 47. PMID 1822724. Ungerleider L, Desimone R (1986). \"Cortical connections of visual area MT in the macaque.\". J Comp Neurol. 248 (2): 190 222. doi: 10.1002/cne.902480204. PMID 3722458. Sincich L, Park K, Wohlgemuth M, Horton J (2004). \"Bypassing V1: a direct geniculate input to area MT.\". Nat Neurosci. 7 (10): 1123 8. doi: 10.1038/nn1318. PMID 15378066. Palmer SM, Rosa MG (2006). \"A distinct anatomical network of cortical areas for analysis of motion in far peripheral vision.\". Eur J Neurosci. 24 (8): 2389 405. Rodman HR, Gross CG, Albright TD (1989) Afferent basis of visual response properties in area MT of the macaque. I. Effects of striate cortex removal. J Neurosci 9 (6):2033-50. Dubner R, Zeki S (1971). \"Response properties and receptive fields of cells in an anatomically defined region of the superior temporal sulcus in the monkey.\". Brain Res. 35 (2): 528 32. doi: 10.1016/0006-8993 (71)90494-X. PMID 5002708.. Maunsell J, Van Essen D (1983). \"Functional properties of neurons in middle temporal visual area of the macaque monkey. I. Selectivity for stimulus direction, speed, and orientation.\". J Neurophysiol. 49 (5): 1127 47. PMID 6864242. Hess, Baker, Zihl (1989). \"The\" motion-blind\" patient: low-level spatial and temporal filters\". Journal of Neuroscience. 9 (5): 1628 1640. Baker, Hess, Zihl (1991). \"Residual motion perception in a\" motion-blind\" patient, assessed with limited-lifetime random dot stimuli\". Journal of Neuroscience. 11 (2): 454 461. Movshon, J. A., Adelson, E. H., Gizzi, M. S., & Newsome, W. T. (1985). The analysis of moving visual patterns. In: C. Chagas, R. Gattass, & C. Gross (Eds. ), Pattern recognition mechanisms (pp. 117-151), Rome: Vatican Press. Britten & Van Wezel 1998 Wilson, H. R., Ferrera, V. P., & Yo, C. (1992). A psychophysically motivated model for two-dimensional motion perception. Vis Neurosci, 9 (1), 79-97. Tinsley, C. J., Webb, B. S., Barraclough, N. E., Vincent, C. J., Parker, A., & Derrington, A. M. (2003). The nature of V1 neural responses to 2D moving patterns depends on receptive-field structure in the marmoset monkey. J Neurophysiol, 90 (2), 930-937. Pack & Born, 2003 Albright T (1984). \"Direction and orientation selectivity of neurons in visual area MT of the macaque.\". J Neurophysiol. 52 (6): 1106 30. PMID 6520628. De Angelis G, Newsome W (1999). \"Organization of disparity-selective neurons in macaque area MT.\". J Neurosci. 19 (4): 1398 415. PMID 9952417. External links The Primary Visual Cortex by Matthew Schmolesky at University of Utah Architecture of the Visual Cortex, by David Hubel at Harvard University Neuro Names ancil-415 - striate area 17Neuro Names ancil-699 - Brodmann area 17 in guenon Brain Maps at UCDavis visual%20cortex Computational Maps in the Visual Cortex at computationalmaps.org Simulator for computational modeling of visual cortex maps at topographica.org See also Brodmann area Cortical area Cortical blindness Feature integration theory List of regions in the human brain Retinotopyvte Brain: telencephalon (cerebrum, cerebral cortex, cerebral hemispheres)Frontal lobe Precentral gyrus ( Primary motor cortex, 4 )Superior frontal gyrus / Frontal eye fields ( 6, 8, 9 ), Middle frontal gyrus ( 46 ), Inferior frontal gyrus / Broca's area ( 44 - Pars opercularis, 45 - Pars triangularis )Orbitofrontal cortex ( 10, 11, 12, 47 )Prefrontal cortex, Premotor cortex Precentral sulcus - Superior frontal sulcus - Inferior frontal sulcus - Olfactory sulcus Parietal lobe Somatosensory cortex ( Primary (1, 2, 3, 43 ), Secondary ( 5 )), Precuneus ( 7m) - Parietal operculum Parietal lobules ( Superior ( 7l ), Inferior ( 40 )), Angular gyrus ( 39 )Intraparietal sulcus, Marginal sulcus Occipital lobe Primary visual cortex (17), ( Cuneus, Lingual gyrus, Lateral occipital gyrus ( 18, 19 )) Calcarine fissure Temporal lobe Primary auditory cortex ( 41, 42 ), Superior temporal gyrus ( 38, 22 / Wernicke's area ), Middle temporal gyrus ( 21 ), Inferior temporal gyrus ( 20) Fusiform gyrus ( 37) Medial temporal lobe ( Amygdala, Parahippocampal gyrus ( 27, 28, 34, 35, 36)Cingulate cortex / gyrus Subgenual area ( 25 ), Anterior cingulate ( 24, 32, 33 ), Posterior cingulate ( 23, 31 ), Retrosplenial cortex ( 26, 29, 30) Callosal sulcus Interlobar sulci/fissureslateral: Central (frontal+parietal), Lateral (frontal+parietal+temporal), Parieto ccipitalmedial: Medial longitudinal, Cingulate (frontal+cingulate ), Collateral (temporal+occipital)White matter tracts Commissural fibers - Association fibers Internal capsule ( Anterior limb, Genu, Posterior limb ), Corona radiata, External capsule, Lamina terminalis, Extreme capsule, Semioval center Olfactory tract, Terminal stria Other Insular cortexgray: Olfactory bulb, Anterior olfactory nucleus, Basal optic nucleus of Meynert, Substantia innominata, Anterior perforated substance Corpus striatum - Limbic lobe Some categorizations are approximations, and some Brodmann areas span gyri.vte Sensory system - Visual system Eye Optic nerve Optic chiasm Optic tract Lateral geniculate nucleus Optic radiation Visual cortex Blobsda: Visuel kortexde: Visueller Cortex el: nl: Visuele cortex sv: Syncentrum Categories: Pages with reference errors Pages with citations using unsupported parameters CS1 maint: Multiple names: authors list CS1 maint: Explicit use of et al. 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"docid": "D312959",
"title": "BrainMind.comNeuroscience",
"text": "The Occipital Lobes Vision, Blind Sight,Hallucinations, Visual Agnosias R. Gabriel Joseph, Ph. D. Simple and complex visual and central/foveal analysis is one of the main functions associated with the occipital lobe (Kaas & Krubitzer 2001; Sereno et al. 1995; Zeki, 2007). However, like the frontal, temporal, and parietal lobes which respond to and process information from a number of modalities, the occipital lobe contains neurons which respond to vestibular, acoustic, visual, visceral, and somesthetic input (Beckers & Zeki 2004; Ferster, et al., 1996; Horen et al., 1972; Jung, 1961; Morrell, 1967; Pigarev 2004; Sereno et al. 1995; Zeki. 2007). Likewise, visual functioning is not restricted to the occipital lobes for over half the primate neocortex is also concerned with visual functions (Reid, 2012; Zeki, 2007). In fact, although much of thalamic-visual- retinal input is directed to the primary visual receptive areas in the occipital lobe (Broadmann's area 17), visual input is also transmitted directly to these other visual areas such as the temporal and parietal lobes, including signals related to rapid motion and object recognition (Haxby et al., 2001; Sereno et al. 1995; Zeki, 2007). For example, and as detailed in chapters 20 and 21, the superior parietal lobe also contains visual cortex and receives peripheral and lower visual input via the optic radiations, whereas the middle and inferior temporal lobes receive foveal and upper visual field input via these fibers (Doty, 1983; Kaas & Krubitzer 2001; Lin et al. 1982; Sereno et al. 1995). There are thus parallel and independent as well as semi-independent visual projection/reception systems within the occipital lobe as well as surrounding visual areas, with the different areas being functionally specialized to analyze different visual details such as color, motion, and object recognition (Zeki, 2007). For example, as based on functional imaging, a cortical area located at the lateral occipital temporal border (referred to as V5), can be independently activated by rapid visual motion, whereas parallel activation of area 17 (also referred to as V1) is not always observed (Zeki, 2007). As will be discussed below, this independent and semi-independent organization of the visual cortex (and other parts of the brain) and the fact that there are mutliple visual areas each of which are functionally specialized, has important implications regarding \"blind sight\" as well as other disconnection syndromes (see chapter 2). That is, these extensive and multiple visual areas also promote multiple fields of visual conscious awareness. There are in fact, over 30 different visual areas that have been distinguished as based on functional specificity, chemistry, physiology, and cytoarchitexture (Felleman & van Essen, 2001; Zeki, 2007). That so much of the human/primate neocortex is concerned with visual functioning is in part a reflection of our arboreal and semi-carnivorous ancestry. That is, early in our evolutionary history, the eyes migrated to the front of the head thereby providing for stereoscopic vision, and adaption which promoted life among the trees and the hunting and killing of small animals. Moreover, cortical layers I and VII (6b) are phylogentically ancient in organization and structure and resemble and may well be an extension of midbrain tissue (Marin-Padilla 1988a) which in turn is visually sensitive. As detailed in chapter 5, it appears that these two cellular layers were initially (and presently) concerned with photoanalysis. THE PRIMARY & ASSOCIATION VISUAL CORTEXIn primates and those carnivoes with their forward facing eyes, axons from the retina form the optic nerve, are organized so that visual information from the same points in visual space can be combined and rerouted at the otpic chiasm, and then directed so that all information arising from the left vs right half of the visual fields are directed to the right vs left half of the occipital lobes and visual cortex. That is, visual information arising in the nasal portion of the right eye, is combined with that from the lateral-temporal portion of the left eye (and vice versa), such that the primary visual area in the right hemisphere receives information from the left half of visual space. However, this information is first received in the lateral geniculate nucleus of the thalamus, each layer of which receives input from only one eye (Casagrande & Joseph, 1978, 1980), the bulk of which is then relayed to the primary visual cortex. The primary visual receiving area (i.e. striate cortex, area 17) is located predominantly within the medial walls and floor of the calcarine sulcus and extends around the lateral convexity. Area 17 is also characterized by rather thin cortical layers, particularly layers II and II, and by its striped appearance which is due to the structure and composition of layer IV. That is, layer IV is divided into three sublayers, with the middle layer containing a rather thick band of cortex (the band of Baillarger/Gennari) which is visible to the naked eye. The association cortices (areas 18 & 19) are also located medially and along the lateral convexity. However, there are also extra-striatal visual association and assimilaton areas located in the superior parietal (area 7) and inferior and middle temporal lobes (Kaas & Krubitzer 2001; Nakamura et al. 2004; Sereno et al. 1995; Tovee et al. 2004). PRE-CORTICAL VISUAL ANALYSISThere is much processing of visual input prior to its reception in the occipital lobe and some visual signals appear to initially bypass the primary and association visual areas (Zeki, 2007). Initially, visual information analysis takes place in the receptor cells (rods and cones) within the retina and then undergoes successive hierarchical stagess of analysis as it is passed through the sequential cell layers of which the retina is composed; i.e. horizontal cells, bipolar cells, amacrine cells, ganglion cells. Information is then relayed via the optic nerve to the lateral geniculate nucleus of the thalamus (Casagrande & Joseph, 1978, 1980; Kaas & Krubitzer 2001) as well as to the pulvinar and superior colliculus, where yet further forms of analysis are performed (see Reid, 2012, for a detailed generalized review). As per the lateral geniculate nucleus (LGN), this structure is organized into 6 layers, each of which receives input from only one eye. However, if for any reason visual input was lost from one eye during early development, those cells innervated by the normal eye apparently grow axonal collaterals which innervate and perhaps functionally suppress the neurons in the adjoining layers which are being denied visual input (Casagrande & Joseph, 1978, 1980). These deprived cells, in turn, grow smaller and atrophy. However, if the normal eye is removed, or if the deprived eye is opened and given forced experience, some of these cells will recover, and so will some aspects of visual functioning (Joseph & Casagrande, 1978, 1980); which indicates that some degree of perceptual processing is occurring within the LGN. Specifically, the LGN appears to engage in the preprocessing of color (processed by \"P\" cells), and contrast (processed by \"K\" cells\"). Moreover, these cells are segregated and project to specific sublayers of the visual cortex; i.e. layer IVa,b,c. From the lateral geniculate and pulvinar, visual stimuli are then transmitted via the optic radiations to the primary visual receiving area, the striate cortex as well as to surrounding areas; e.g. via the pulvinar and superior colliculus (Doty, 1983; Kaas & Krubitzer 2001; Snyder & Diamond, 1968; Tigges et al. 1983). These pathways leading to the visual cortex maintain a strict topographical relationship. Within the visual cortex immediately adjacent groups of neurons respond to visual information from neighboring regions within the retina (Kaas & Krubitzer 2001). As noted, most of these signals, at least those from the LGN, are received in layer IVa,b,c --layers which contain \"simple cells\" (described below) and to a lesser extent layer VI and VII or area 17. From the visual cortex this information is then transferred back to the lateral geniculate nucleus of the thalamus (from which it was first relayed), to the superior colliculus (Kawamuara et al. 1974) and to the association areas 18 and 19 as well as the middle temporal lobe (Buchel et al., 1998; Doty, 1983; Kaas & Krubitzer 2001; Lin et al. 1982; Price, 2007; Sereno et al. 1995) where higher order processing occurs (Tovee et al. 2004). For example, when viewing or reading words, the left medial extrastriate visual cortex is activated (Peterson et al., 1990), whereas the right inferior occipital lobe becomes active when looking at pictures (Price, 2007). These visual association areas also transmit signals back to the primary area, such that highly processed information is passed back and forth, perhaps on a need to know basis. However, as noted, these visual areas are also capable of acting autonomously without pre- or post processing in the primary visual cortex such as via projections form the pulvinar to V5 (Zeki, 2007). A similar arrangement seems to characterized information reception and transfer in the auditory, somesthetic, and motor cortices as well. That is, information transferred from the thalamus to the neocortex is then transferred back to the thalamus as well as to the adjacent association areas which then transfer information back and forth on a need to know basis. In this manner a feedback loop is constructed so that information transmission from the thalamus to the cortex and within the neocortex, can be enhanced, diminished, or altered depending on neocortical requirements. Nevertheless, although different areas can act autonomously, in general, visual stimuli are received in the primary area and then relayed to the association areas18 and 19 (where further analyses take place) this information is transmitted back to area 17 and to the temporal and parietal lobe where poly modal associations are performed (Beckers & Zeki 1995; Martinez-Millan & Hollander, 1975; Tigges et al. 1983; Tovee et al. 2004; Zeki. 1978b). NEOCORTICAL COLUMNAR ORGANIZATIONThroughout the striate cortex neurons with similar receptive properties are stacked in columns (Hubel & Wiesel, 1968, 1974). Indeed, one column of cells may respond to a certain visual orientation and the cells in the next column to an orientation of a slightly different angle. Moreover, columns exist for color (Zeki, 1974), location, movement, etc. In addition, since certain cells respond predominantly to input from one eye, there are ocular (eye) dominance columns as well (Hubel & Wiesel, 1968, 1974). A similar columnar arrangement in regard to somesthetic input is maintained in the parietal lobe. Within these ocular dominance columns, the visual cortex is also organized so that they match and parallel input received within the retina, thus creating a retinotopic map. That is, adjacent cells in these columns receive input from adjacent cells in the retina. However, there is also almost a 50% overlap between columns, such that there are shared receptive fields, such that single cells can perceive more than one point in space--which in turn allows for a smooth transition which making eye and head movements. Indeed, neurons of a particular column, although communicating predominantly with those in the same column, also communicate with immediately adjacent columns, such that a considerable amount of parrallel communication occurs (Dow, 1974; Kaas & Krubitzer 2001). That is, information is anlyazed vertically and horizontally. so as to create a series of superimposed mosaics of the visual word. SIMPLE, COMPLEX, LOWER- & HIGHER ORDER HYPERCOMPLEX FEATURE DETECTORSThe visual cortex is made up of a variety of cell types each of which is concerned with the analysis of different visual features (Ferster, et al., 1996; Hubel & Wiesel, 1959, 1962, 1968; Kaas & Krubitzer 2001; Sereno et al. 1995). These include simple, complex, and (higher & lower order) hypercomplex cells which are distributed disproportionately throughout areas 17,18, 19. To briefly summarize, simple cells appear to be involved in the initial analysis of incoming visual cortical input, and are most sensitive to slowly moving stimuli. They are found predominantly within area 17 and in layer IVa,b,c,. Some are sensitive to stimuli moving in one direction, whereas others may respond to stimuli moving in any direction. In fact, almost 95% of the neurons in area 17 are responsive to stimuli moving only in one direction, but not the direction of movement. In addition, simple cells are responsive to the particular position and orientation a stimulus may take. However, for a simple cell to fire, a stimulus must assume a specific orientation and position. Simple cells relay this processed information to the far more numerous complex cells which are found predominantly in layers II and III and V, which interact and communicate with one another including with layer IV which receives thalamic input. Each complex cell receives input from several simple cells. Complex cells are also concerned with orientation of the stimulus. However, these cells are more flexible and will respond and analyze a stimulus regardless of its particular orientation. These cells via the combined input from simple cells, are probably involved in the earliest stages of actual form perception, i.e. the determination of the outline of an object. A considerable number of complex cells receive converging input from both eyes, the remainder being monocular. Complex cells are found predominantly within area 18. Hypercomplex cells are concerned with the analysis of discontinuity, angles and corners, as well as movement, position, and orientation. That is, these cells respond selectively to certain visual configurations and thus act so as to determine precise geometric form. It is also via the action of these cells (in conjuction with visual neurons in the temporal lobe) that the first stages of visual closure are initiated. This in part requires that the functional activity of these cells be suppressed such that when presented with an incomplete figure these cells are overridden and the brain is able to \"fill in the gaps\" in stimuli perceived. It is also for this reason that one does not notice his or her \"blind spot\"; it is filled in. Hypercomplex cells are found predominantly within area 19. STRIATE CORTEX: AREA 17The primary visual cortex, area 17, is located predominantly within the medial walls of the cerebral hemispheres, extending only minimally along the lateral convexity. This area is often referred to as \"striate\" because the incoming fibers from the optic radiations form a stripe along the cortical surface which can be seen by the naked eye. Areas 18 and 19 do not have this striped appearance. Like the primary motor and somesthetic cortices, a greater degree of cellular representation is maintained for those areas which are the most densely innervated and of the most sensory importance, i.e., the fovea (Daniel & Whitteridge, 1961; Hubel & Wiesel, 1979; Kaas & Krubitzer 2001). Indeed, the central part of the retina has a cortical representation which is 35 times more detailed than that of the periphery. This is particularly important in that the fovea contains cells which are most sensitive to the detection and representation of form. Although all neuron types are found within the striate cortex, simple and complex cells predominate. Hence, the primary receiving area is predominantly involved in the analysis of color, slow movement, position, and orientation (Zeki, 2007); i.e. the most elementary aspects of form and visual stimulus perception. The primary visual cortex, however, receives fibers from non-visual brain areas as well. These include brainstem nuclei, the pontine and mesencephalic reticular formation, the lateral amygdala, and lateral hypothalamus (Doty, 1983; Tigges et al. 1983). Processing in the primary region can thus be enhanced or diminished via reticular influences and emotional-motivational concerns. In this manner, if a stimulus is emotionally significant greater visual attention will be directed at the object. Conversely, bilateral destruction of area 17 can result in loss of visual recognition capabilities -even with sparing of the association areas (Humphrey & Weiskrantz 1967; Weiskrantz & Cowey 1963). However, awareness of moving objects and visual-spatial orientation is preserved. Visual preservation with primary occipital destruction has been referred to as \"blind sight\" (see below). HALLUCINATIONS. Electrical stimulation, tumors, seizures, or trauma involving the striate cortex may produces simple visual hallucinations, such as sparks, tongues of flames, colors and flashes of lights (Penfield, 1954; Tarachow, 1941). Objects may seem to become exceedingly large (macropsia) or small (micropsia), blurred in terms of outline, stretched out in a single dimension, or colors may become modified or even erased (Hecaen & Albert, 1978). Sometimes simple geometric forms may be reported. Usually the hallucination is restricted to one half of the visual field. That is, if the seizure is in the right occipital lobe, the hallucination will appear in the left visual field. Although elementary hallucinations are usually associated with abnormalities involving the occipital lobe they may occur with temporal lobe lesions or electrical stimulation (Penfield & Rasmussen, 1950; Tarachow, 1941). ASSOCIATION AREAS 18 & 19Areas 18 and 19 are are involved in the translation and interpretations of visual impressions transmitted from area 17. Although simple and complex cells are found in the association cortex, this region is predominantly populated by hypercomplex (both higher and lower order) neurons --most of which are concerned with the determination of precise geometric form as well as the assimilation of signals transmitted from the primary cortex (Kaas & Krubitzer 2001). In contrast to the neurons within area 17, many of the cells within area 18 receive binocular input and can be activated by either eye (Hubel & Wiesel, 1970). This same pattern of bincularity is evident in the parietal association area. It is via the action of these cells that one is able to gather information regarding distance, discrepancies in stimulus location and thus determine depth and achieve stereoscopic vision (Blakemore, 1970a; Hubel & Wiesel, 1970a). Indeed, some association neurons will only fire when a target is a definite distance from the eye. Many of the neurons in this region, particularly area 19, receive higher order converging input from the parietal and temporal lobe. For example, in addition to visual input, neurons in the superior portions of area 19 respond to tactile and proprioceptive stimuli, whereas those in the inferior portions respond to auditory signals (Morrell, 1967). It is probably in this manner (in conjunction with subcortical connections with, for example, the superior colliculus) that one is able to orient toward and gaze upon an auditory stimulus as well as maintain stablization of the head (via proprioceptive-vestbibular input) while engaged in visual search. Hence, overall, the visual association area appears to be involved in the initial analysis of form, distance, and depth perception, as well as the performance of visual closure. It is thus heavily involved in the association of various visual attributes so that a variety of qualities may be ascertained. This would include an objects shape, length, thickness, and color (Sereno et al. 1995). THE TEMPORAL/PARIETAL VISUAL AREASThe visual association areas also maintain intimate relationships with the parietal visual regions (area 7) as well as the visual areas in the middle and inferior temporal lobes (ares 37) including V5 (the lateral occipital-temporal junction). The temporal visual areas are in turn reciprocally interconnected with area 7 and areas 17, 18, 19. As noted, whereas the temporal lobes perform complex form recognition and central and upper visual field analysis, the parietal lobes observe the periphery and lower visual field (where the hands and feet are most likely to be viewed) and together these cortical regions compute and make possible, eye-hand, or hand-object coordination. Hence, a complex interactional visual loop is maintained. For example, the inferior-medial temporal lobe is concerned with form perception and the analysis of emotional-motivational significance and transmits this information to area 7. Area 7 is involved in visual attention, visual fixation, and the analysis of distance, depth, and objects within grasping distance. Area V5 (at the temporal occipital border) perceive motion. Hence, through this temporal/occipital/parietal pathway, the individual can recognize and fixate on the object (temporal lobe), determine the speed at which it is traveling (V5) and reach out and grasp it (parietal lobe). As noted, the temporal parietal visual areas are also interconnected with areas 17, 18, and 19, and receive their own autonomous visual input, via, for example, the pulvinar and midbrain. Moreover, the temporal parietal visual areas receive some visual signals in advance of the primary and association visual areas. Area V5, for example, perceive rapid movement, and if injured or deactivated, the ability to perceive rapid movement is diminished or abolished, whereas slow motion perception is maintained due to preservation of the occipital visual areas (Zeki, 2007). Moreover, fast moving stimuli are perceived and activate area V5 in advance of area 17, which in turn is excited by slow moving stimuli in advance of area V5. Hence, V5 receives information from the retina regarding fast moving objects, information that bypasses the primary visual area (Zeki, 2007); a very adaptive relationship, at least from an evolutionary and life-preservative perspective, for under some circumstances it would be most advantageous to perceive something that was moving rapidly, such as a predator, than something less dangerous that was moving slowly. MULTIPLE VISUAL REALITIESAs detailed in chapters 2, 10, the brain is not only interactional, but is characterized by normal discontinuities where some areas do not always communicate together efficiently. That is, the functioning of the brain is not always in parallel, such that some areas function in semi-isolation or semi-independently giving rise to multiple streams of conscious awareness which may not always correspond to reality. The same can be said even regarding those areas of the brain which are ostensibly concerned with the same visual stimulus, such as auditory or vision as is the case with V5 and areas 17, such that when these stimuli are processed, an internal reality which is slightly different from external reality may be produced. According to Zeki (2007, pp. 170-171) the evidence has \"led us to the concept of dynamic parallelism, by which we mean that while both areas can be healthy and functional in a normal brain, which area gets activated first depends on the nature of the stimulus.\" However, as also pointed out by Zeki (2007), even within the visual system the various \"perceptual systems are therefore different as are the processing systems\" and \"that there is no synchronizer in the brain capable of setting the results of the operations of the two processing-perceptual systems to time zero... that we thought was the hallmark of our visual experience.... the brain, therefore missychronizes and misbinds or rather more accurately, it binds the results of its processing-perceptual systems, not what happens in real time in the real world. \"HOMONYMOUS HEMIANOPSIA & QUADRANTANOPSIAMassive unilateral destruction of the visual cortices results in blindness in the contralateral temporal visual field and ipsilateral nasal visual field. Hence, a left visual cortex lesion produced a right homonymous hemianopsia. However, these visual disturbances may also result from destruction of the optic radiations or optic tract. It is noteworthy that patients are often unaware of having lost half their sight, particularly with right occipital lesions. Nevertheless, patients may complain of bumping into people and objects they cannot see. As noted, above, the parietal lobes are concerned with the lower visual fields, whereas the temporal lobes receive massive upper visual field projections. Thus, lesions to the inferior or superior occipital lobe can result in an upper or lower visual field homonymous quadrantanopsia. HALLUCINATIONSElectrical stimulation of or lesions involving areas 18 and 19 can produce complex visual hallucinations (Foerster, 1929, cited by Brodal, 1981 & Hecaen & Albert, 1978; Tarachow, 1941), such as images of men, animals, various objects and geometric figures, liliputian-type individuals, including micropsias and macropsias (see Luria, 1980; & Hecaen & Albert, 1978, for review). Sometimes objects may seem to become telescoped and far away, wheras in other situations, when approached, objects may seem to loom and become exceedingly large. Complex hallucinations are usually quite vivid and fully formed and the patient may think what he sees is a real (Hecaen & Albert, 1978). Foerester (1928, cited by Heacen & Albert, 1978) reported a ptient who hallucinated a butterfly then attempted to catch it when area 19 was elecrically stimulated. Another hallucinated a dog and then called to it, denying the possibility that it was not real. Complex hallucinations, although usually associated with tumors or abnormal activation of the visual association area, have also been reported with parietal-occipital involvement (Russell & Whitty, 1955), occipital-temporal, or inferior-temporal damage (Mullan & Penfield, 1959; Tarachow, 1941; Teuber et al., 1960), or with lesions of the occipital pole and convexity (Hecaen & Albert, 1978)Laterality. According to Hecaen and Albert (1978) based on their review of the international literature, although simple hallucinations are likely following damage to either hemisphere, complex hallucinations are usually associated with right rather than left cerebral lesions (Teuber et al., 1960; Mullan & Penfield, 1959; Hecaen & Albert, 1978). CORTICAL BLINDNESSLesions of the occipital lobe, especially if the entire visual cortex is ablated, result in cortical blindness, such that pattern and form vision is lost. Rather, what is left is the ability to discriminate only between different fluexes in luminous energy, i.e. lightness and darkness (Brindley et al. 1969; Brodal, 1981, Hecaen & Albert, 1978; Weiskrantz, 1963). If damage is restricted to the occipital lobe of only one of the hemispheres, patients will lose patterned vision for the opposite half of the visual field (i.e. a hemianopsia). This is not the same as unilateral neglect or inattention. However, if the lesion is sufficiently large and involves the right parietal area as well, the patient may suffer from both hemianopsia and neglect. Nevertheless, if only a portion of the visual cortex is destroyed, vision is lost only for the corresponding quadrant of the visual field (referred to as a scotoma). However, in cases of partial cortical blindness, patients are able to make compensatory eye movements and are not terribly troubled by their disability (Luria, 1980). Indeed, frequenty patients have no awareness that they have lost a quadrant or even half of their visual field. Hence, this must be tested for. \"BLIND SIGHT\"Although considered somewhat controversial, it has been reported that although blind (due to destruction of the primary visual cortex), some individuals are able to indicate the presence or absence of a moving stimulus within the \"blind\" portion of their visual field (Holmes, 1918; Riddoch, 1917; Scharli, Harman & Hogben, 2012; Weiskrantz, 1986, 1996; Zeki, 2007), and even differentiate between various objects, although not knowing what they are (Humphrey & Weiskrantz 1967; Weiskrantz & Cowey 1963). Using forced choice procedures, although \"blind\" some patients can localize visual targets and perceive moving objects. In one case it has been reported that a patient who denied visual perception and with a diagnosis of cortical blindness, was able to correctly name objects, colors, famous faces, facial emotions, as well as read various single words with greater than 50% accuracy (Hartmann et al. 2001). Visual preservation following area 17 lesions has been referred to as \"blind sight\" (Weiskrantz, et al. 1974; Weiskrantz, 1996). Although blind, these patients may avoid obstacles, and correctly retrieve desired objects, and thus appear to have some residual visual functions even though they verbally claim no conscious awareness of the visual stimulus and thus have no verbal awareness that they can see (Poppel, Held & Frost, 1973). Nevertheless, although the verbal aspects of consciousness have been disconnected from the visual cortex and claims it cannot see, the patient continues to behave as if visual input is still being received; hence the term \"blind sight. \"However, it has also been argued that \"blind sight\" is not really \"blind sight\" and that \"useful visual function is preserved only when a critical amount of area 17 is spared (Celesia et al. 2001). For example, using PET and SPECT studies, Celesia and colleagues (2001) found that among those with visual cortical destruction and \"blind sight\", that islands of preserved area 17 functioning were observed. According to Celesia et al. (2001) those with complete area 17 destruction that patients do not demonstrate signs of \"blind sight.\" This view is in error, however as \"blind sight\" has also been demonstrated with evidence of no functional activity in area 17 (Barbur, et al., 2003; Zeki, 2007). Possibly, although cortically blind, patients are able to recognize moving objects, or in some cases, correctly move about in space, due to the preservation of intact subcortical nuclei involved in visual orientation, i.e. via the so called \"second (retino-collicular- pulvinar-extrastriate) visual system\" (Schneider, 1969; Weller 1988) which projects to temporal occipital junction, i.e. area V5. For example, Barbour and colleagues (2003), describe a patient GY, who had suffered damage to the occipital lobe at age 8, rendered hemianopi yet was able to demonstrate blindsight. Using functional imaging, it was found that although there was no activity in the primary visual area when shown a fast moving object, that V5 became highly active, and that GY was able to see a \"shadow.\" However, when asked to clarify what he had seen, GY replied that it was more of a \"feeling\" (Zeki, 2007). Given that V5 became active, this suggests that blindsight, at least in this case, was due in part to preserved visual functioning in the temporal occipital junction. Consistent with this view is the case presented by Hartmann et al. (2001). Although denying visual perception, the patient was able to name objects, colors, and so on, when the stimuli were placed in the upper visual field. The upper visual fields are associated with the inferior temporal lobe, which are the recipients of fibers from the \"second visual system\" as well as from the visual neocortex. Hence, in cases of disconnection and blind sight due to occipital lesions, complex visual input may still reach the temporal lobe, and may therefore be directed to the auditory areas via a secondary route so that associatd \"feelings\" of seeing something can be communicated, and in some cases, so that objects can be named, although the patient continues to deny visual perception. Presumably, those who are \"cortically\" blind but demonstrate \"blind sight\" coupled, in some cases, with the ability to turn the head and orient, can accomplish these acts apparently because undamaged midbrain, thalamic, and neocortical tissues (e.g. temporal/parietal lobe) involved in visual functioning continue to function normally (Milner & Goodale, 1995; Stoerig, 1996). That is, tissues in the midbrain, thalamus, or the temporal/parietal lobe, continue to process visual input, but are nevertheless, disconnected from the \"dominant\" stream of verbal consciousness mediated by the left hemisphere due to the injury to the occipital lobe. Although \"cortically blind\" the eyes are functional, and visual impressions are transmitted via the optic nerve directly to the midbrain visual colliculus, and via the optic tracts and optic radiations to the lateral geniculate nucleus of the thalamus and other forebrain structures including the visual areas in the temporal and parietal lobe (Milner & Goodale, 1995; Stoerig, 1996) which in turn may transmit visual input to those islands of striate cortex which remain intact (Wessinger, Fendrich, & Gazzaniga, 2007), but which are unable to communicate with the language areas of the brain, which, in failing to receive visual signals, claims to have no knowledge of the visual world. Nevertheless, visual processing continues outside of linguistic conscious-awareness, and patients may report that their behavior is guided by \"non-visual feelings\" (Scharli, et al., 2012). Hence, although disconnected form the language axis, which reports only \"non-visual feelings\" these isolated visual areas may continue to mediate behavior, perhaps via connections with the midbrain--a structure which is responsive primarily to moving stimuli and which is triggers head turning in response to moving stimuli (Blessing, 2007; Klemm & Vertes, 1990). Consider, for example, the classic cases of blindsight first described by Riddoch (1917). According to Riddoch (1917) although these patients had suffered extensive destruction of the primary visual areas, they remained \"conscious of something moving when the object oscillate... and that.... the consciousness of something moving kept up a continual desire to turn the head. \"The fact that these and other patients with blind sight may have a feeling of seeing movement, are/or experience a desire to turn the head, and/or correctly reach out and grasp or move around objects, directly implicates the midbrain visual colliculus as this structure is able to detect movement and different gradations of light and shadow (Davidson & Bender, 2001), and (via the lower brainstem) can direct head turning, groping and grasping, and even walking (Blessing, 2007; Klemm & Vertes, 1990). However, as noted above, due to massive destruction of primary visual cortex, and as areas 17 and V5 as well as other neocortical areas interact, there is a disruption of the feedback loop which enables the language axis to receive these visual impressions, other than, in some cases, through the experience of \"feelings.\" Nevertheless, one does not need language or a neocortex in order to see movement or perform simple visually-guied movements, which is why creatures such as reptiles, frogs, etc., are capable of complex visually guided behaviors even though they never evolved language or neocortex. Humans, however, have evolved neocortex, and the primary visual receiving areas hierarchically analyze these subcortical visual signals which are then transferred to the adjoining visual association areas thereby forming complex visual associations (Kaas & Krubitzer, 2001; Milner & Goodale, 1995; Sereno, Dale, & Reppas, 1995). These complex associations are then transmitted to the language axis which then names and verbally describes what the individual sees (Critchley, 1964; Geschwind, 1965; Joseph, 1982). These visual impressions come to be associated with language and thus with linguistic consciousness. However, with massive injuries to the primary visual cortex, the language axis no longer receives visual input, and the patient reports that he or she is blind and cannot see, though, in some cases, they avoid obstacles and can reach for desired objects. Thus patients with \"blind sight\" demonstrate at least two disconnected streams of mental activity, one of which utilizes language to deny visual experience other than through the experience of \"feelings\", and a second non-verbal form of subcortical or isolated neocortical mental activity that is capable of seeing and/or controlling movements of the body in response to certain visual stimuli. Moreover, these multiple modes of conscious-awareness, including those supporting blindsight may wax and wane, \"resulting in blindsight in some test sessions and in conscious awareness of the same stimuli in others... which raises the interesting question of whether the brain switches from one neural system to another during the waxing and waning of consciousness (Zeki, 2007, p. 175). DENIAL OF BLINDNESSMore frequently, however, patients with cortical blindness (such as following massive lesions of the visual cortex) seem initially quite confused, indifferent regarding their condition, and report a variety of hallucinatory experiences which may be complex or elementary in form. Moreover, frequently these patients will initially deny they are blind (Redlich & Dorsey, 1945) --a condition referred to as Anton's syndrome. For example, a number of patients described by Redlich and Dorsey (1945), although bumping into furniture and unable to recognize objects held before them, invented elaborate excuses for their errors and failure to see; e.g. claiming that it is a little dark and they need their glasses, or conversely, that they see better at home. That is, these patients confabulate. As discussed in chapter 10, these confabulatory abnormalties are sometimes due to a disconnection such that the Language Axis, failing to receive information from the visual cortex (i.e. that it cannot see), responds instead to associations from intact areas which concern \"seeing\". That is, the Language Axis does not know that it is blind because information concerning blindness is not being received from the proper neural channels. It is also possible that these patients deny being blind, because subcortically they are still able to see. Hence, although at a neocortical level there is no sight, subcortically there remains an unconscious awareness of the visual world. VISUAL AGNOSIA & ALEXIAAs based on functional imaging studies, the left medial extrastriate visual cortex becomes activated when reading or viewing words (Peterson et al., 1990), whereas the right inferior occipital lobe becomes active when looking at pictures (Price, 2007). In addition to letters, words, and pictures, complex form and object recognition is also subserved by the extra-striate visual areas in the occipital lobe, the ventral-inferior areas in particular, adjacent to the temporal lobe (Buchel et al., 1998; Haxby, et al., 2001). This has been demonstrated not only by functional imaging (Buchel et al., 1998; Price, 2007), but direct cortical recoding (Nobre et al., 2004), and electrical stimulation (Luders et al., 1986). In fact, both normal, cogenitally blind, and late-blind subject display activity in this area (Buchel et al., 1998). If injured, patients may suffer from reading and naming deficits (Rapcsak, et al., 2002); a condition referred to as phonological alexia (e.g., Miozzo & Caramazza, 1998). Moreover, patients with developmental dyslexia have been found to have abnormalities in this area (Rumsey et al., 2007). However, in addition to, or depending on the nature and exact location of the lesion, patients may suffer from agnosia. Visual agnosia is a condition where the patient loses the capacity to visually recognize objects, although visual sensory functioning is largely normal. This condition often arises with lesions involving the inferior medial occipital lobe. In general, objects are detected but they lose the ability to evoke meaning and cannot be correctly identified or named (Critchley, 1964; Davidoff & De Bleser 2004; Shelton et al. 2004; Teuber, 1968). The percept becomes stripped of its meaning. For example, if shown a comb, the patient might have no idea as to what it is or what it might be used for. If asked to guess they may call it a harmonica or a tiny box. If shown a pair of spectacles, they may call it a \"bicycle\", or \"two spoons\". A picture of a dial telephone may be described a a \"Clock\", etc. (Luria, 1980)Many patients are unable to sort pictures or objects into categories or match pictures with the actual object such that there appears to be a deficit in the ability to not only recognize but to classify visual percepts (Hecaen, et al. 1974). Moreover, in severe cases they are unable to point to objects that are named. Nevertheless, this is not a naming disorder (e.g. Davidoff & De Bleser 2004), because regardless of modality, anomics continue to have word finding and naming difficulties. In contrast, those with agnosia show enhanced recognition if an object is presented via a second intact modality (e.g. if they palpate it by hand). Thus agnosia can often be limited to a single input channel, i.e. visual vs. tactual. Moreover, If an object is used in context, recognition can be greatly enhanced (Rubens, 2003). Some patients may complain that objects change while they are looking at them, and /or that they disappear; a condition which suggests optic ataxia. Usually, however, the deficit is conceptual rather than perceptual. There are however, to major forms of agnosia, and different subtypes as well, which can be produced by damage to tissues mediating complex visual perception or lesions disconnecting the IPL, for example, from visual, somesthetic, or auditory input. For example, one type of agnosia, \"apperceptive visual agnosia\" refers to a disturbance in perceptual and visual-motor integration, such that patients have difficulty copying or matching various objects. This latter form of agnosia has been associated with lesions to the parietal occipital cortex (Mizuno, et al., 1996), as well as to bilateral damage to the inferior-occipital cortex (Shelton, et al., 2004). For example, although they may be able to accurately describe, draw or copy various aspects of the object they are shown (Albert, et al,. 1975; Mack & Boller, 1977; Rubens & benson, 1971) they fail to correctly draw the entire object. Moreover, if asked to trace rather than copy, these patients may trace over and over the outlines of objects or drawing but cannot recognize where they started. Thus they seem unable to synthesize visual details into an integral whole (Luria, 1980). That is, patients may recognize an isolated detail (e.g. the dial of a phone) but are unable to relate it to the headset, etc. (see Shelton et al. 2004) Hence, if asked what they have been shown, they may erroneously extrapolate from the detail perceived and thus confabulate a concept. With increasing object complexity, or if surrounded by other objects, or if the object is presented in pictorial (vs. actual) form, or if unnecessary lines are drawn across the picture, the abilty to recognize the object deteriorates even futher (Luria, 1980; Rubens & Benson, 1971). By contrast, associative visual agnosia, which is a deficit in naming, such that auditory equivalents cannot be matched to a visual perception, is associated with left inferior and middle temporal (area 37) occipital abnormalities (Giannokapoulos et al., 2012), which may be accompanied with alexia (Feinberg et al., 2004), as well as to lesions to and atrophy of the parietal occipital cortex (Mizuno, et al., 1996). Agnosic individuals also often (but not always, Davidoff & De Bleser 2004) have difficulty with reading (Albert, Reches & Silverberg, 1975; Mack & Boller, 1977; Rubens & Benson, 1971) and may suffer from prosopagnosia and/or impaired color naming (Mack & Boller, 197; Shelton et al. 2004). Interestingly, in some cases visual memory be intact (Rubens, 1979). Like alexia, agnosia can occur following lesions to the medial and deep mesial portion of the left occipital lobe (Feinberg, et al., 2004). The left inferior temporal lobe and posterior hippocampus may also be damaged in some cases (Shelton et al. 2004). In some cases, it is likely that agnosia is due not only to tissue destruction but to tissue disconnection. That is, if the visual form recognition neurons in the temporal lobe are no longer able to receive input from the visual association areas, then this particular region becomes \"cortically blind\" and form recognition is prevented. However, like some other disconnection syndromes, if a different input channel is employed, i.e. if the object is verbally described or tactually explored, recognition is enhanced. PROSOPAGNOSIA. Prosopagnosia is a severe disturbance in the ability to recognize the faces of friends, loved ones, or pets (De Renzi, 1986; De Renzi, et. al., 1968; De Renzi & Spinnler, 1966; Evans et al. 1995; Hecaen & Angelergues, 1962; Landis, et al. 1986; Levine, 1978; Whitely & Warrington, 1977l ). Some patients may in fact be unable to recognize their own face in the mirror. Nevertheless, they usually realize that a face is a face; they just don't know who the face belongs to. In this regard, prosopagnosia is not a visual agnosia as described above, where the patient cannot recognize that a chair is a chair or a clock a clock. A number of authors have erroneously argued that prosopagnosia is due to bilateral injuries involving the inferior and medial occipital lobe visual association areas. Nevertheless, although frequently such individuals do indeed suffer from bilateral injuries, in many cases the lesions are restricted to the right hemisphere and involve the occipital and inferior temporal regions (De Renzi, 1986; De Renzi et. al., 1968; De Renzi & Spinnler, 1966; Evans et al. 1995; Hecaen & Angelergues, 1962; Landis et al., 1986; Levine, 1978; Whitely & Warrington, 1977; Young et al. 1995), although frontal lesions (Braun et al. 2004), and right parietal lesions (Young et al. 2002) may also disrupt facial recognition. By contrast, prosopagnosia does not usually result from lesions restricted to the left half of the brain, whereas loss of facial recognition with frontal and parietal lesions are more likely due to visual neglect and visual scanning abnormalities. Although prosopagnosia could be explained from a disconnection perspective, it is likely that the actual face identification neurons have been destroyed whereas neurons involved in the recognition of facial parts have been preserved. SIMULTANAGNOSIASimultanagnosia occurs with left hemisphere damage and is an inability to see more than one thing, or all aspects of an item, at a time (Bousen & Humphrey, 2012; Kinsbourne & Warrington, 1962, 1964; Laeng, et al., 2012; Rizzo & Robin 1990). For example, some patients complain of seeing things only in a piecemeal fashion such that objects look fragmented. In fact, by surrounding the object with other objects perceptual recognition deteriorates even further. This condition is sometimes accompanied by abnormal eye movements (Luria, 1980). These individuals often have difficulty shifting gaze and/or performing visual search tasks such that their ability to scan and visually explore the environment is drastically reduced (Bousen & Humphrey, 2012; Rizzo & Robin 1990). As described by Luria (1980), this is due to a breakdown in the ability to perform serial feature-by-feature visual analysis. Visual attention is often largely limited to the central visual field whereas the periphery is ignored (Hecaen & Ajuriaguerra, 1954; Luria, 1973, 1980). However, patients complain that even objects in the central visual field tend to disappear as they stare at them (Rizzo & Robin 1990). Simultagnosia has been described following lesions to the frontal eye fields and following bilateral superior occipital lobe lesions (Rizzo & Hurtig, 2002). In many cases the lesion may be localized to the superior occipital-parietal region (area 7). Hence, the patient is no longer able to maintain visual fixation and cannot adequately focus on an object or explore its parts. This disorder has also been referred to as Balints syndrome as well as optic ataxia, paralysis of gaze, and concentric narrowing of the visual field. IMPAIRED COLOR RECOGNITIONIn this condition, although sometimes able to correctly name objects patients cannot correctly name, match, and identify colors or point to colors named by the examiner. No, this is not due to color blindness. Frequently individuals with color imperception also display prosopanosia (Green & Lessel, 1977; Meadows, 1974b). De Renzi & Spinnler (1967) found that 23& of those with right cerebral damaged and 12% of those with left sided destruction had difficulty with color matching (Lhermitte et al., 1969). On the otherhand, some investigators note that impairments of color perception are frequently secondary to bilateral inferior occiptial lobe damage (Green & Lessell, 1977; Meadows, 1974a; Shelton et al. 2004). In addition, almost 50% of those with aphasia demonstrate deficient color naming and color identification (De Renzi & Spinnler, 1967; De Renzi et al., 1972). However, color perception per se is largely intact among aphasic individuals. OVERVIEWThe primary visual cortex is located predominantly within the medial walls of the cerebral hemispheres and is concerned with the elementary aspects of form perception. Damage limited to this area will usually affect foveal vision and/or give rise to simple hallucinations. From the primary area information is then relayed to the association areas, 18 and 19, where complex analysis including form recognition, position and analysis of depth take place. Damage involving these areas and the primary region can cause cortical blindness or hemianopsia if only one hemisphere is lesioned. Destruction or abnormal activity in areas 18 and 19 are associated with the formation of complex hallucinations. Visual information is next relayed to area 7 in the parietal lobe and to the inferior temporal lobule, where higher order analysis and multimodal processing occurs. Damage to the parietal-occipital borders may result in abnormalities involving depth and form perception as well as visual neglect. Destruction of the temporal-occipital regions can give rise to visual agnosias and an inability to recognize complex objects and faces. The occipital lobes also appear to be lateralized in regard to certain capabilities such as facial recognition. For example, destruction of the right occipital region is associated with prosopagnosia, and abnormal activity in this area is more likely to give rise to complex visual hallucinations. Brain Mind Lecture 9: Thalamus, Striatum, Basal Ganglia Brain Mind Lecture 7: Temporal Lobes Brain Mind Lecture 7: Temporal Lobes Brain Mind Lecture 5: Frontal Lobes "
},
{
"docid": "D312959",
"title": "Anatomy of the Brain",
"text": "Anatomy of the Brain The brain serves many important functions. It gives meaning to things that happen in the world surrounding us. Through the five senses of sight, smell, hearing, touch and taste, the brain receives messages, often many at the same time. The brain controls thoughts, memory and speech, arm and leg movements and the function of many organs within the body. It also determines how people respond to stressful situations (i.e. writing of an exam, loss of a job, birth of a child, illness, etc.) by regulating heart and breathing rates. The brain is an organized structure, divided into many components that serve specific and important functions. The weight of the brain changes from birth through adulthood. At birth, the average brain weighs about one pound, and grows to about two pounds during childhood. The average weight of an adult female brain is about 2.7 pounds, while the brain of an adult male weighs about three pounds. The Nervous System The nervous system is commonly divided into the central nervous system and the peripheral nervous system. The central nervous system is made up of the brain, its cranial nerves and the spinal cord. The peripheral nervous system is composed of the spinal nerves that branch from the spinal cord and the autonomous nervous system (divided into the sympathetic and parasympathetic nervous system). The Cell Structure of the Brain The brain is made up of two types of cells: neurons and glial cells, also known as neuroglia or glia. The neuron is responsible for sending and receiving nerve impulses or signals. Glial cells are non-neuronal cells that provide support and nutrition, maintain homeostasis, form myelin and facilitate signal transmission in the nervous system. In the human brain, glial cells outnumber neurons by about 50 to one. Glial cells are the most common cells found in primary brain tumors. When a person is diagnosed with a brain tumor, a biopsy may be done, in which tissue is removed from the tumor for identification purposes by a pathologist. Pathologists identify the type of cells that are present in this brain tissue, and brain tumors are named based on this association. The type of brain tumor and cells involved impact patient prognosis and treatment. The Meninges The brain is housed inside the bony covering called the cranium. The cranium protects the brain from injury. Together, the cranium and bones that protect the face are called the skull. Between the skull and brain is the meninges, which consist of three layers of tissue that cover and protect the brain and spinal cord. From the outermost layer inward they are: the dura mater, arachnoid and pia mater. Dura Mater: In the brain, the dura mater is made up of two layers of whitish, nonelastic film or membrane. The outer layer is called the periosteum. An inner layer, the dura, lines the inside of the entire skull and creates little folds or compartments in which parts of the brain are protected and secured. The two special folds of the dura in the brain are called the falx and the tentorium. The falx separates the right and left half of the brain and the tentorium separates the upper and lower parts of the brain. Arachnoid: The second layer of the meninges is the arachnoid. This membrane is thin and delicate and covers the entire brain. There is a space between the dura and the arachnoid membranes that is called the subdural space. The arachnoid is made up of delicate, elastic tissue and blood vessels of varying sizes. Pia Mater: The layer of meninges closest to the surface of the brain is called the pia mater. The pia mater has many blood vessels that reach deep into the surface of the brain. The pia, which covers the entire surface of the brain, follows the folds of the brain. The major arteries supplying the brain provide the pia with its blood vessels. The space that separates the arachnoid and the pia is called the subarachnoid space. It is within this area that cerebrospinal fluid flows. Cerebrospinal Fluid Cerebrospinal fluid (CSF) is found within the brain and surrounds the brain and the spinal cord. It is a clear, watery substance that helps to cushion the brain and spinal cord from injury. This fluid circulates through channels around the spinal cord and brain, constantly being absorbed and replenished. It is within hollow channels in the brain, called ventricles, that the fluid is produced. A specialized structure within each ventricle, called the choroid plexus, is responsible for the majority of CSF production. The brain normally maintains a balance between the amount of CSF that is absorbed and the amount that is produced. However, disruptions in this system may occur. The Ventricular System The ventricular system is divided into four cavities called ventricles, which are connected by a series of holes, called foramen, and tubes. Two ventricles enclosed in the cerebral hemispheres are called the lateral ventricles (first and second). They each communicate with the third ventricle through a separate opening called the Foramen of Munro. The third ventricle is in the center of the brain, and its walls are made up of the thalamus and hypothalamus. The third ventricle connects with the fourth ventricle through a long tube called the Aqueduct of Sylvius. CSF flowing through the fourth ventricle flows around the brain and spinal cord by passing through another series of openings. Brain Components and Functions Brainstem The brainstem is the lower extension of the brain, located in front of the cerebellum and connected to the spinal cord. It consists of three structures: the midbrain, pons and medulla oblongata. It serves as a relay station, passing messages back and forth between various parts of the body and the cerebral cortex. Many simple or primitive functions that are essential for survival are located here. The midbrain is an important center for ocular motion while the pons is involved with coordinating eye and facial movements, facial sensation, hearing and balance. The medulla oblongata controls breathing, blood pressure, heart rhythms and swallowing. Messages from the cortex to the spinal cord and nerves that branch from the spinal cord are sent through the pons and the brainstem. Destruction of these regions of the brain will cause \"brain death.\" Without these key functions, humans cannot survive. The reticular activating system is found in the midbrain, pons, medulla and part of the thalamus. It controls levels of wakefulness, enables people to pay attention to their environments and is involved in sleep patterns. Originating in the brainstem are 10 of the 12 cranial nerves that control hearing, eye movement, facial sensations, taste, swallowing and movements of the face, neck, shoulder and tongue muscles. The cranial nerves for smell and vision originate in the cerebrum. Four pairs of cranial nerves originate from the pons: nerves five through eight. Cerebellum The cerebellum is located at the back of the brain beneath the occipital lobes. It is separated from the cerebrum by the tentorium (fold of dura). The cerebellum fine tunes motor activity or movement, e.g. the fine movements of fingers as they perform surgery or paint a picture. It helps one maintain posture, sense of balance or equilibrium, by controlling the tone of muscles and the position of limbs. The cerebellum is important in one's ability to perform rapid and repetitive actions such as playing a video game. In the cerebellum, right-sided abnormalities produce symptoms on the same side of the body. Cerebrum The cerebrum, which forms the major portion of the brain, is divided into two major parts: the right and left cerebral hemispheres. The cerebrum is a term often used to describe the entire brain. A fissure or groove that separates the two hemispheres is called the great longitudinal fissure. The two sides of the brain are joined at the bottom by the corpus callosum. The corpus callosum connects the two halves of the brain and delivers messages from one half of the brain to the other. The surface of the cerebrum contains billions of neurons and glia that together form the cerebral cortex. The cerebral cortex appears grayish brown in color and is called the \"gray matter.\" The surface of the brain appears wrinkled. The cerebral cortex has sulci (small grooves), fissures (larger grooves) and bulges between the grooves called gyri. Scientists have specific names for the bulges and grooves on the surface of the brain. Decades of scientific research have revealed the specific functions of the various regions of the brain. Beneath the cerebral cortex or surface of the brain, connecting fibers between neurons form a white-colored area called the \"white matter. \"The cerebral hemispheres have several distinct fissures. By locating these landmarks on the surface of the brain, it can effectively be divided into pairs of \"lobes.\" Lobes are simply broad regions of the brain. The cerebrum or brain can be divided into pairs of frontal, temporal, parietal and occipital lobes. Each hemisphere has a frontal, temporal, parietal and occipital lobe. Each lobe may be divided, once again, into areas that serve very specific functions. The lobes of the brain do not function alone: they function through very complex relationships with one another. Messages within the brain are delivered in many ways. The signals are transported along routes called pathways. Any destruction of brain tissue by a tumor can disrupt the communication between different parts of the brain. The result will be a loss of function such as speech, the ability to read or the ability to follow simple spoken commands. Messages can travel from one bulge on the brain to another (gyri to gyri), from one lobe to another, from one side of the brain to the other, from one lobe of the brain to structures that are found deep in the brain, e.g. thalamus, or from the deep structures of the brain to another region in the central nervous system. Research has determined that touching one side of the brain sends electrical signals to the other side of the body. Touching the motor region on the right side of the brain would cause the opposite side or the left side of the body to move. Stimulating the left primary motor cortex would cause the right side of the body to move. The messages for movement and sensation cross to the other side of the brain and cause the opposite limb to move or feel a sensation. The right side of the brain controls the left side of the body and vice versa. So if a brain tumor occurs on the right side of the brain that controls the movement of the arm, the left arm may be weak or paralyzed. Cranial Nerves There are 12 pairs of nerves that originate from the brain itself. These nerves are responsible for very specific activities and are named and numbered as follows: Olfactory: Smell O ptic: Visual fields and ability to see Oculomotor: Eye movements; eyelid opening Trochlear: Eye movements Trigeminal: Facial sensation Abducens: Eye movements Facial: Eyelid closing; facial expression; taste sensation Auditory/vestibular: Hearing; sense of balance Glossopharyngeal: Taste sensation; swallowing Vagus: Swallowing; taste sensation Accessory: Control of neck and shoulder muscles Hypoglossal: Tongue movement Hypothalamus The hypothalamus is a small structure that contains nerve connections that send messages to the pituitary gland. The hypothalamus handles information that comes from the autonomic nervous system. It plays a role in controlling functions such as eating, sexual behavior and sleeping; and regulates body temperature, emotions, secretion of hormones and movement. The pituitary gland develops from an extension of the hypothalamus downwards and from a second component extending upward from the roof of the mouth. The Lobes Frontal Lobes The frontal lobes are the largest of the four lobes responsible for many different functions. These include motor skills such as voluntary movement, speech, intellectual and behavioral functions. The areas that produce movement in parts of the body are found in the primary motor cortex or precentral gyrus. The prefrontal cortex plays an important part in memory, intelligence, concentration, temper and personality. The premotor cortex is a region found beside the primary motor cortex. It guides eye and head movements and a person s sense of orientation. Broca's area, important in language production, is found in the frontal lobe, usually on the left side. Occipital Lobes These lobes are located at the back of the brain and enable humans to receive and process visual information. They influence how humans process colors and shapes. The occipital lobe on the right interprets visual signals from the left visual space, while the left occipital lobe performs the same function for the right visual space. Parietal Lobes These lobes interpret simultaneously, signals received from other areas of the brain such as vision, hearing, motor, sensory and memory. A person s memory, and the new sensory information received, give meaning to objects. Temporal Lobes These lobes are located on each side of the brain at about ear level, and can be divided into two parts. One part is on the bottom (ventral) of each hemisphere, and the other part is on the side (lateral) of each hemisphere. An area on the right side is involved in visual memory and helps humans recognize objects and peoples' faces. An area on the left side is involved in verbal memory and helps humans remember and understand language. The rear of the temporal lobe enables humans to interpret other people s emotions and reactions. Limbic System This system is involved in emotions. Included in this system are the hypothalamus, part of the thalamus, amygdala (active in producing aggressive behavior) and hippocampus (plays a role in the ability to remember new information). Pineal Gland This gland is an outgrowth from the posterior or back portion of the third ventricle. In some mammals, it controls the response to darkness and light. In humans, it has some role in sexual maturation, although the exact function of the pineal gland in humans is unclear. Pituitary Gland The pituitary is a small gland attached to the base of the brain (behind the nose) in an area called the pituitary fossa or sella turcica. The pituitary is often called the \"master gland\" because it controls the secretion of hormones. The pituitary is responsible for controlling and coordinating the following: Growth and development The function of various body organs (i.e. kidneys, breasts and uterus)The function of other glands (i.e. thyroid, gonads, and adrenal glands)Posterior Fossa This is a cavity in the back part of the skull which contains the cerebellum, brainstem and cranial nerves 5-12. Thalamus The thalamus serves as a relay station for almost all information that comes and goes to the cortex. It plays a role in pain sensation, attention and alertness. It consists of four parts: the hypothalamus, the epythalamus, the ventral thalamus and the dorsal thalamus. The basal ganglia are clusters of nerve cells surrounding the thalamus. Language and Speech Functions In general, the left hemisphere or side of the brain is responsible for language and speech. Because of this, it has been called the \"dominant\" hemisphere. The right hemisphere plays a large part in interpreting visual information and spatial processing. In about one-third of individuals who are left-handed, speech function may be located on the right side of the brain. Left-handed individuals may need specialized testing to determine if their speech center is on the left or right side prior to any surgery in that area. Many neuroscientists believe that the left hemisphere and perhaps other portions of the brain are important in language. Aphasia is simply a disturbance of language. Certain parts of the brain are responsible for specific functions in language production. There are many types of aphasias, each depending upon the brain area that is affected, and the role that area plays in language production. There is an area in the frontal lobe of the left hemisphere called Broca s area. It is next to the region that controls the movement of facial muscles, tongue, jaw and throat. If this area is destroyed, a person will have difficulty producing the sounds of speech, because of the inability to move the tongue or facial muscles to form words. A person with Broca's aphasia can still read and understand spoken language, but has difficulty speaking and writing. There is a region in the left temporal lobe called Wernicke's area. Damage to this area causes Wernicke's aphasia. An individual can make speech sounds, but they are meaningless (receptive aphasia) because they do not make any sense. The AANS does not endorse any treatments, procedures, products or physicians referenced in these patient fact sheets. This information is provided as an educational service and is not intended to serve as medical advice. Anyone seeking specific neurosurgical advice or assistance should consult his or her neurosurgeon, or locate one in your area through the AANS Find a Board-certified Neurosurgeon online tool. "
},
{
"docid": "D312959",
"title": "Motor Responses",
"text": "Motor Responses The defining characteristic of the somatic nervous system is that it controls skeletal muscles. Somatic senses inform the nervous system about the external environment, but the response to that is through voluntary muscle movement. The term voluntary suggests that there is a conscious decision to make a movement. However, some aspects of the somatic system use voluntary muscles without conscious control. One example is the ability of our breathing to switch to unconscious control while we are focused on another task. However, the muscles that are responsible for the basic process of breathing are also utilized for speech, which is entirely voluntary. Cortical Responses Let s start with sensory stimuli that have been registered through receptor cells and the information relayed to the CNS along ascending pathways. In the cerebral cortex, the initial processing of sensory perception progresses to associative processing and then integration in multimodal areas of cortex. These levels of processing can lead to the incorporation of sensory perceptions into memory, but more importantly, they lead to a response. The completion of cortical processing through the primary, associative, and integrative sensory areas initiates a similar progression of motor processing, usually in different cortical areas. Whereas the sensory cortical areas are located in the occipital, temporal, and parietal lobes, motor functions are largely controlled by the frontal lobe. The most anterior regions of the frontal lobe the prefrontal areas are important for executive functions, which are those cognitive functions that lead to goal-directed behaviors. These higher cognitive processes include working memory, which has been called a mental scratch pad, that can help organize and represent information that is not in the immediate environment. The prefrontal lobe is responsible for aspects of attention, such as inhibiting distracting thoughts and actions so that a person can focus on a goal and direct behavior toward achieving that goal. The functions of the prefrontal cortex are integral to the personality of an individual, because it is largely responsible for what a person intends to do and how they accomplish those plans. A famous case of damage to the prefrontal cortex is that of Phineas Gage, dating back to 1848. He was a railroad worker who had a metal spike impale his prefrontal cortex ( link ). He survived the accident, but according to second-hand accounts, his personality changed drastically. Friends described him as no longer acting like himself. Whereas he was a hardworking, amiable man before the accident, he turned into an irritable, temperamental, and lazy man after the accident. Many of the accounts of his change may have been inflated in the retelling, and some behavior was likely attributable to alcohol used as a pain medication. However, the accounts suggest that some aspects of his personality did change. Also, there is new evidence that though his life changed dramatically, he was able to become a functioning stagecoach driver, suggesting that the brain has the ability to recover even from major trauma such as this. Phineas Gage The victim of an accident while working on a railroad in 1848, Phineas Gage had a large iron rod impaled through the prefrontal cortex of his frontal lobe. After the accident, his personality appeared to change, but he eventually learned to cope with the trauma and lived as a coach driver even after such a traumatic event. (credit b: John M. Harlow, MD)Secondary Motor Cortices In generating motor responses, the executive functions of the prefrontal cortex will need to initiate actual movements. One way to define the prefrontal area is any region of the frontal lobe that does not elicit movement when electrically stimulated. These are primarily in the anterior part of the frontal lobe. The regions of the frontal lobe that remain are the regions of the cortex that produce movement. The prefrontal areas project into the secondary motor cortices, which include the premotor cortex and the supplemental motor area. Two important regions that assist in planning and coordinating movements are located adjacent to the primary motor cortex. The premotor cortex is more lateral, whereas the supplemental motor area is more medial and superior. The premotor area aids in controlling movements of the core muscles to maintain posture during movement, whereas the supplemental motor area is hypothesized to be responsible for planning and coordinating movement. The supplemental motor area also manages sequential movements that are based on prior experience (that is, learned movements). Neurons in these areas are most active leading up to the initiation of movement. For example, these areas might prepare the body for the movements necessary to drive a car in anticipation of a traffic light changing. Adjacent to these two regions are two specialized motor planning centers. The frontal eye fields are responsible for moving the eyes in response to visual stimuli. There are direct connections between the frontal eye fields and the superior colliculus. Also, anterior to the premotor cortex and primary motor cortex is Broca s area. This area is responsible for controlling movements of the structures of speech production. The area is named after a French surgeon and anatomist who studied patients who could not produce speech. They did not have impairments to understanding speech, only to producing speech sounds, suggesting a damaged or underdeveloped Broca s area. Primary Motor Cortex The primary motor cortex is located in the precentral gyrus of the frontal lobe. A neurosurgeon, Walter Penfield, described much of the basic understanding of the primary motor cortex by electrically stimulating the surface of the cerebrum. Penfield would probe the surface of the cortex while the patient was only under local anesthesia so that he could observe responses to the stimulation. This led to the belief that the precentral gyrus directly stimulated muscle movement. We now know that the primary motor cortex receives input from several areas that aid in planning movement, and its principle output stimulates spinal cord neurons to stimulate skeletal muscle contraction. The primary motor cortex is arranged in a similar fashion to the primary somatosensory cortex, in that it has a topographical map of the body, creating a motor homunculus (see link ). The neurons responsible for musculature in the feet and lower legs are in the medial wall of the precentral gyrus, with the thighs, trunk, and shoulder at the crest of the longitudinal fissure. The hand and face are in the lateral face of the gyrus. Also, the relative space allotted for the different regions is exaggerated in muscles that have greater enervation. The greatest amount of cortical space is given to muscles that perform fine, agile movements, such as the muscles of the fingers and the lower face. The power muscles that perform coarser movements, such as the buttock and back muscles, occupy much less space on the motor cortex. Descending Pathways The motor output from the cortex descends into the brain stem and to the spinal cord to control the musculature through motor neurons. Neurons located in the primary motor cortex, named Betz cells, are large cortical neurons that synapse with lower motor neurons in the brain stem or in the spinal cord. The two descending pathways travelled by the axons of Betz cells are the corticobulbar tract and the corticospinal tract, respectively. Both tracts are named for their origin in the cortex and their targets either the brain stem (the term bulbar refers to the brain stem as the bulb, or enlargement, at the top of the spinal cord) or the spinal cord. These two descending pathways are responsible for the conscious or voluntary movements of skeletal muscles. Any motor command from the primary motor cortex is sent down the axons of the Betz cells to activate upper motor neurons in either the cranial motor nuclei or in the ventral horn of the spinal cord. The axons of the corticobulbar tract are ipsilateral, meaning they project from the cortex to the motor nucleus on the same side of the nervous system. Conversely, the axons of the corticospinal tract are largely contralateral, meaning that they cross the midline of the brain stem or spinal cord and synapse on the opposite side of the body. Therefore, the right motor cortex of the cerebrum controls muscles on the left side of the body, and vice versa. The corticospinal tract descends from the cortex through the deep white matter of the cerebrum. It then passes between the caudate nucleus and putamen of the basal nuclei as a bundle called the internal capsule. The tract then passes through the midbrain as the cerebral peduncles, after which it burrows through the pons. Upon entering the medulla, the tracts make up the large white matter tract referred to as the pyramids ( link ). The defining landmark of the medullary-spinal border is the pyramidal decussation, which is where most of the fibers in the corticospinal tract cross over to the opposite side of the brain. At this point, the tract separates into two parts, which have control over different domains of the musculature. Corticospinal Tract The major descending tract that controls skeletal muscle movements is the corticospinal tract. It is composed of two neurons, the upper motor neuron and the lower motor neuron. The upper motor neuron has its cell body in the primary motor cortex of the frontal lobe and synapses on the lower motor neuron, which is in the ventral horn of the spinal cord and projects to the skeletal muscle in the periphery. Appendicular Control The lateral corticospinal tract is composed of the fibers that cross the midline at the pyramidal decussation (see link ). The axons cross over from the anterior position of the pyramids in the medulla to the lateral column of the spinal cord. These axons are responsible for controlling appendicular muscles. This influence over the appendicular muscles means that the lateral corticospinal tract is responsible for moving the muscles of the arms and legs. The ventral horn in both the lower cervical spinal cord and the lumbar spinal cord both have wider ventral horns, representing the greater number of muscles controlled by these motor neurons. The cervical enlargement is particularly large because there is greater control over the fine musculature of the upper limbs, particularly of the fingers. The lumbar enlargement is not as significant in appearance because there is less fine motor control of the lower limbs. Axial Control The anterior corticospinal tract is responsible for controlling the muscles of the body trunk (see link ). These axons do not decussate in the medulla. Instead, they remain in an anterior position as they descend the brain stem and enter the spinal cord. These axons then travel to the spinal cord level at which they synapse with a lower motor neuron. Upon reaching the appropriate level, the axons decussate, entering the ventral horn on the opposite side of the spinal cord from which they entered. In the ventral horn, these axons synapse with their corresponding lower motor neurons. The lower motor neurons are located in the medial regions of the ventral horn, because they control the axial muscles of the trunk. Because movements of the body trunk involve both sides of the body, the anterior corticospinal tract is not entirely contralateral. Some collateral branches of the tract will project into the ipsilateral ventral horn to control synergistic muscles on that side of the body, or to inhibit antagonistic muscles through interneurons within the ventral horn. Through the influence of both sides of the body, the anterior corticospinal tract can coordinate postural muscles in broad movements of the body. These coordinating axons in the anterior corticospinal tract are often considered bilateral, as they are both ipsilateral and contralateral. Watch this video to learn more about the descending motor pathway for the somatic nervous system. The autonomic connections are mentioned, which are covered in another chapter. From this brief video, only some of the descending motor pathway of the somatic nervous system is described. Which division of the pathway is described and which division is left out? Extrapyramidal Controls Other descending connections between the brain and the spinal cord are called the extrapyramidal system. The name comes from the fact that this system is outside the corticospinal pathway, which includes the pyramids in the medulla. A few pathways originating from the brain stem contribute to this system. The tectospinal tract projects from the midbrain to the spinal cord and is important for postural movements that are driven by the superior colliculus. The name of the tract comes from an alternate name for the superior colliculus, which is the tectum. The reticulospinal tract connects the reticular system, a diffuse region of gray matter in the brain stem, with the spinal cord. This tract influences trunk and proximal limb muscles related to posture and locomotion. The reticulospinal tract also contributes to muscle tone and influences autonomic functions. The vestibulospinal tract connects the brain stem nuclei of the vestibular system with the spinal cord. This allows posture, movement, and balance to be modulated on the basis of equilibrium information provided by the vestibular system. The pathways of the extrapyramidal system are influenced by subcortical structures. For example, connections between the secondary motor cortices and the extrapyramidal system modulate spine and cranium movements. The basal nuclei, which are important for regulating movement initiated by the CNS, influence the extrapyramidal system as well as its thalamic feedback to the motor cortex. The conscious movement of our muscles is more complicated than simply sending a single command from the precentral gyrus down to the proper motor neurons. During the movement of any body part, our muscles relay information back to the brain, and the brain is constantly sending revised instructions back to the muscles. The cerebellum is important in contributing to the motor system because it compares cerebral motor commands with proprioceptive feedback. The corticospinal fibers that project to the ventral horn of the spinal cord have branches that also synapse in the pons, which project to the cerebellum. Also, the proprioceptive sensations of the dorsal column system have a collateral projection to the medulla that projects to the cerebellum. These two streams of information are compared in the cerebellar cortex. Conflicts between the motor commands sent by the cerebrum and body position information provided by the proprioceptors cause the cerebellum to stimulate the red nucleus of the midbrain. The red nucleus then sends corrective commands to the spinal cord along the rubrospinal tract. The name of this tract comes from the word for red that is seen in the English word ruby. A good example of how the cerebellum corrects cerebral motor commands can be illustrated by walking in water. An original motor command from the cerebrum to walk will result in a highly coordinated set of learned movements. However, in water, the body cannot actually perform a typical walking movement as instructed. The cerebellum can alter the motor command, stimulating the leg muscles to take larger steps to overcome the water resistance. The cerebellum can make the necessary changes through the rubrospinal tract. Modulating the basic command to walk also relies on spinal reflexes, but the cerebellum is responsible for calculating the appropriate response. When the cerebellum does not work properly, coordination and balance are severely affected. The most dramatic example of this is during the overconsumption of alcohol. Alcohol inhibits the ability of the cerebellum to interpret proprioceptive feedback, making it more difficult to coordinate body movements, such as walking a straight line, or guide the movement of the hand to touch the tip of the nose. Visit this site to read about an elderly woman who starts to lose the ability to control fine movements, such as speech and the movement of limbs. Many of the usual causes were ruled out. It was not a stroke, Parkinson s disease, diabetes, or thyroid dysfunction. The next most obvious cause was medication, so her pharmacist had to be consulted. The side effect of a drug meant to help her sleep had resulted in changes in motor control. What regions of the nervous system are likely to be the focus of haloperidol side effects? Ventral Horn Output The somatic nervous system provides output strictly to skeletal muscles. The lower motor neurons, which are responsible for the contraction of these muscles, are found in the ventral horn of the spinal cord. These large, multipolar neurons have a corona of dendrites surrounding the cell body and an axon that extends out of the ventral horn. This axon travels through the ventral nerve root to join the emerging spinal nerve. The axon is relatively long because it needs to reach muscles in the periphery of the body. The diameters of cell bodies may be on the order of hundreds of micrometers to support the long axon; some axons are a meter in length, such as the lumbar motor neurons that innervate muscles in the first digits of the feet. The axons will also branch to innervate multiple muscle fibers. Together, the motor neuron and all the muscle fibers that it controls make up a motor unit. Motor units vary in size. Some may contain up to 1000 muscle fibers, such as in the quadriceps, or they may only have 10 fibers, such as in an extraocular muscle. The number of muscle fibers that are part of a motor unit corresponds to the precision of control of that muscle. Also, muscles that have finer motor control have more motor units connecting to them, and this requires a larger topographical field in the primary motor cortex. Motor neuron axons connect to muscle fibers at a neuromuscular junction. This is a specialized synaptic structure at which multiple axon terminals synapse with the muscle fiber sarcolemma. The synaptic end bulbs of the motor neurons secrete acetylcholine, which binds to receptors on the sarcolemma. The binding of acetylcholine opens ligand-gated ion channels, increasing the movement of cations across the sarcolemma. This depolarizes the sarcolemma, initiating muscle contraction. Whereas other synapses result in graded potentials that must reach a threshold in the postsynaptic target, activity at the neuromuscular junction reliably leads to muscle fiber contraction with every nerve impulse received from a motor neuron. However, the strength of contraction and the number of fibers that contract can be affected by the frequency of the motor neuron impulses. Reflexes This chapter began by introducing reflexes as an example of the basic elements of the somatic nervous system. Simple somatic reflexes do not include the higher centers discussed for conscious or voluntary aspects of movement. Reflexes can be spinal or cranial, depending on the nerves and central components that are involved. The example described at the beginning of the chapter involved heat and pain sensations from a hot stove causing withdrawal of the arm through a connection in the spinal cord that leads to contraction of the biceps brachii. The description of this withdrawal reflex was simplified, for the sake of the introduction, to emphasize the parts of the somatic nervous system. But to consider reflexes fully, more attention needs to be given to this example. As you withdraw your hand from the stove, you do not want to slow that reflex down. As the biceps brachii contracts, the antagonistic triceps brachii needs to relax. Because the neuromuscular junction is strictly excitatory, the biceps will contract when the motor nerve is active. Skeletal muscles do not actively relax. Instead the motor neuron needs to quiet down, or be inhibited. In the hot-stove withdrawal reflex, this occurs through an interneuron in the spinal cord. The interneuron s cell body is located in the dorsal horn of the spinal cord. The interneuron receives a synapse from the axon of the sensory neuron that detects that the hand is being burned. In response to this stimulation from the sensory neuron, the interneuron then inhibits the motor neuron that controls the triceps brachii. This is done by releasing a neurotransmitter or other signal that hyperpolarizes the motor neuron connected to the triceps brachii, making it less likely to initiate an action potential. With this motor neuron being inhibited, the triceps brachii relaxes. Without the antagonistic contraction, withdrawal from the hot stove is faster and keeps further tissue damage from occurring. Another example of a withdrawal reflex occurs when you step on a painful stimulus, like a tack or a sharp rock. The nociceptors that are activated by the painful stimulus activate the motor neurons responsible for contraction of the tibialis anterior muscle. This causes dorsiflexion of the foot. An inhibitory interneuron, activated by a collateral branch of the nociceptor fiber, will inhibit the motor neurons of the gastrocnemius and soleus muscles to cancel plantar flexion. An important difference in this reflex is that plantar flexion is most likely in progress as the foot is pressing down onto the tack. Contraction of the tibialis anterior is not the most important aspect of the reflex, as continuation of plantar flexion will result in further damage from stepping onto the tack. Another type of reflex is a stretch reflex. In this reflex, when a skeletal muscle is stretched, a muscle spindle receptor is activated. The axon from this receptor structure will cause direct contraction of the muscle. A collateral of the muscle spindle fiber will also inhibit the motor neuron of the antagonist muscles. The reflex helps to maintain muscles at a constant length. A common example of this reflex is the knee jerk that is elicited by a rubber hammer struck against the patellar ligament in a physical exam. A specialized reflex to protect the surface of the eye is the corneal reflex, or the eye blink reflex. When the cornea is stimulated by a tactile stimulus, or even by bright light in a related reflex, blinking is initiated. The sensory component travels through the trigeminal nerve, which carries somatosensory information from the face, or through the optic nerve, if the stimulus is bright light. The motor response travels through the facial nerve and innervates the orbicularis oculi on the same side. This reflex is commonly tested during a physical exam using an air puff or a gentle touch of a cotton-tipped applicator. Watch this video to learn more about the reflex arc of the corneal reflex. When the right cornea senses a tactile stimulus, what happens to the left eye? Explain your answer. Watch this video to learn more about newborn reflexes. Newborns have a set of reflexes that are expected to have been crucial to survival before the modern age. These reflexes disappear as the baby grows, as some of them may be unnecessary as they age. The video demonstrates a reflex called the Babinski reflex, in which the foot flexes dorsally and the toes splay out when the sole of the foot is lightly scratched. This is normal for newborns, but it is a sign of reduced myelination of the spinal tract in adults. Why would this reflex be a problem for an adult? Chapter Review The motor components of the somatic nervous system begin with the frontal lobe of the brain, where the prefrontal cortex is responsible for higher functions such as working memory. The integrative and associate functions of the prefrontal lobe feed into the secondary motor areas, which help plan movements. The premotor cortex and supplemental motor area then feed into the primary motor cortex that initiates movements. Large Betz cells project through the corticobulbar and corticospinal tracts to synapse on lower motor neurons in the brain stem and ventral horn of the spinal cord, respectively. These connections are responsible for generating movements of skeletal muscles. The extrapyramidal system includes projections from the brain stem and higher centers that influence movement, mostly to maintain balance and posture, as well as to maintain muscle tone. The superior colliculus and red nucleus in the midbrain, the vestibular nuclei in the medulla, and the reticular formation throughout the brain stem each have tracts projecting to the spinal cord in this system. Descending input from the secondary motor cortices, basal nuclei, and cerebellum connect to the origins of these tracts in the brain stem. All of these motor pathways project to the spinal cord to synapse with motor neurons in the ventral horn of the spinal cord. These lower motor neurons are the cells that connect to skeletal muscle and cause contractions. These neurons project through the spinal nerves to connect to the muscles at neuromuscular junctions. One motor neuron connects to multiple muscle fibers within a target muscle. The number of fibers that are innervated by a single motor neuron varies on the basis of the precision necessary for that muscle and the amount of force necessary for that motor unit. The quadriceps, for example, have many fibers controlled by single motor neurons for powerful contractions that do not need to be precise. The extraocular muscles have only a small number of fibers controlled by each motor neuron because moving the eyes does not require much force, but needs to be very precise. Reflexes are the simplest circuits within the somatic nervous system. A withdrawal reflex from a painful stimulus only requires the sensory fiber that enters the spinal cord and the motor neuron that projects to a muscle. Antagonist and postural muscles can be coordinated with the withdrawal, making the connections more complex. The simple, single neuronal connection is the basis of somatic reflexes. The corneal reflex is contraction of the orbicularis oculi muscle to blink the eyelid when something touches the surface of the eye. Stretch reflexes maintain a constant length of muscles by causing a contraction of a muscle to compensate for a stretch that can be sensed by a specialized receptor called a muscle spindle. Interactive Link Questions Watch this video to learn more about the descending motor pathway for the somatic nervous system. The autonomic connections are mentioned, which are covered in another chapter. From this brief video, only some of the descending motor pathway of the somatic nervous system is described. Which division of the pathway is described and which division is left out? Visit this site to read about an elderly woman who starts to lose the ability to control fine movements, such as speech and the movement of limbs. Many of the usual causes were ruled out. It was not a stroke, Parkinson s disease, diabetes, or thyroid dysfunction. The next most obvious cause was medication, so her pharmacist had to be consulted. The side effect of a drug meant to help her sleep had resulted in changes in motor control. What regions of the nervous system are likely to be the focus of haloperidol side effects? Watch this video to learn more about the reflex arc of the corneal reflex. When the right cornea senses a tactile stimulus, what happens to the left eye? Explain your answer. Watch this video to learn more about newborn reflexes. Newborns have a set of reflexes that are expected to have been crucial to survival before the modern age. These reflexes disappear as the baby grows, as some of them may be unnecessary as they age. The video demonstrates a reflex called the Babinski reflex, in which the foot flexes dorsally and the toes splay out when the sole of the foot is lightly scratched. This is normal for newborns, but it is a sign of reduced myelination of the spinal tract in adults. Why would this reflex be a problem for an adult? Chapter Review Which region of the frontal lobe is responsible for initiating movement by directly connecting to cranial and spinal motor neurons?prefrontal cortexsupplemental motor areapremotor cortexprimary motor cortex Which extrapyramidal tract incorporates equilibrium sensations with motor commands to aid in posture and movement?tectospinal tractvestibulospinal tractreticulospinal tractcorticospinal tract Which region of gray matter in the spinal cord contains motor neurons that innervate skeletal muscles?ventral horndorsal hornlateral hornlateral column What type of reflex can protect the foot when a painful stimulus is sensed?stretch reflexgag reflexwithdrawal reflexcorneal reflex What is the name for the topographical representation of the sensory input to the somatosensory cortex?homunculushomo sapienspostcentral gyrusprimary cortex Critical Thinking Questions The prefrontal lobotomy is a drastic and largely out-of-practice procedure used to disconnect that portion of the cerebral cortex from the rest of the frontal lobe and the diencephalon as a psychiatric therapy. Why would this have been thought necessary for someone with a potentially uncontrollable behavior? If a reflex is a limited circuit within the somatic system, why do physical and neurological exams include them to test the health of an individual? Glossaryanterior corticospinal tractdivision of the corticospinal pathway that travels through the ventral (anterior) column of the spinal cord and controls axial musculature through the medial motor neurons in the ventral (anterior) horn Betz cellsoutput cells of the primary motor cortex that cause musculature to move through synapses on cranial and spinal motor neurons Broca s arearegion of the frontal lobe associated with the motor commands necessary for speech productioncerebral pedunclessegments of the descending motor pathway that make up the white matter of the ventral midbraincervical enlargementregion of the ventral (anterior) horn of the spinal cord that has a larger population of motor neurons for the greater number of and finer control of muscles of the upper limbcorneal reflexprotective response to stimulation of the cornea causing contraction of the orbicularis oculi muscle resulting in blinking of the eyecorticobulbar tractconnection between the cortex and the brain stem responsible for generating movementcorticospinal tractconnection between the cortex and the spinal cord responsible for generating movementexecutive functionscognitive processes of the prefrontal cortex that lead to directing goal-directed behavior, which is a precursor to executing motor commandsextrapyramidal systempathways between the brain and spinal cord that are separate from the corticospinal tract and are responsible for modulating the movements generated through that primary pathwayfrontal eye fieldsarea of the prefrontal cortex responsible for moving the eyes to attend to visual stimuliinternal capsulesegment of the descending motor pathway that passes between the caudate nucleus and the putamenlateral corticospinal tractdivision of the corticospinal pathway that travels through the lateral column of the spinal cord and controls appendicular musculature through the lateral motor neurons in the ventral (anterior) hornlumbar enlargementregion of the ventral (anterior) horn of the spinal cord that has a larger population of motor neurons for the greater number of muscles of the lower limbpremotor cortexcortical area anterior to the primary motor cortex that is responsible for planning movementspyramidal decussationlocation at which corticospinal tract fibers cross the midline and segregate into the anterior and lateral divisions of the pathwaypyramidssegment of the descending motor pathway that travels in the anterior position of the medullared nucleusmidbrain nucleus that sends corrective commands to the spinal cord along the rubrospinal tract, based on disparity between an original command and the sensory feedback from movementreticulospinal tractextrapyramidal connections between the brain stem and spinal cord that modulate movement, contribute to posture, and regulate muscle tonerubrospinal tractdescending motor control pathway, originating in the red nucleus, that mediates control of the limbs on the basis of cerebellar processingstretch reflexresponse to activation of the muscle spindle stretch receptor that causes contraction of the muscle to maintain a constant lengthsupplemental motor areacortical area anterior to the primary motor cortex that is responsible for planning movementstectospinal tractextrapyramidal connections between the superior colliculus and spinal cordvestibulospinal tractextrapyramidal connections between the vestibular nuclei in the brain stem and spinal cord that modulate movement and contribute to balance on the basis of the sense of equilibriumworking memoryfunction of the prefrontal cortex to maintain a representation of information that is not in the immediate environment This work is licensed under a Creative Commons Attribution 4.0 International License . You can also download for free at http://cnx.org/contents/14fb4ad7-39a1-4eee-ab6e-3ef2482e3e22@8.119Attribution: For questions regarding this license, please contact partners@openstaxcollege.org. If you use this textbook as a bibliographic reference, then you should cite it as follows: Open Stax College, Anatomy and Physiology. Open Stax CNX. http://cnx.org/contents/14fb4ad7-39a1-4eee-ab6e-3ef2482e3e22@8.119. If you redistribute this textbook in a print format, then you must include on every physical page the following attribution: \"Download for free at http://cnx.org/contents/14fb4ad7-39a1-4eee-ab6e-3ef2482e3e22@8.119 . \"If you redistribute part of this textbook, then you must retain in every digital format page view (including but not limited to EPUB, PDF, and HTML) and on every physical printed page the following attribution: \"Download for free at http://cnx.org/contents/14fb4ad7-39a1-4eee-ab6e-3ef2482e3e22@8.119 .\" "
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"docid": "D312959",
"title": "Flashcard Machine -create, study and share online flash cards",
"text": "Flashcard Machine -create, study and share online flash cards My Flashcards Flashcard Library About Contribute Help Sign In Create Account Search Home Flashcards Physiology Chapters 9 and 10Shared Flashcard Set Details Title Chapters 9 and 10Description Exam 2Total Cards 34Subject Physiology Level Undergraduate 3Created 10/18/2008Click here to study/print these flashcards . Create your own flash cards! Sign up here . Additional Physiology Flashcards Cards Term The human brain weighs about and is made up of . Definition1.4 kg (~3 lbs) ; 10 12 neurons Term It is with different regions having . The glial cell type involved in barriers and compartmentalization. Definitioncompartmentalized; different functions; ependymal Term What is the largest region of the brain? It is the . Definition Cerebrum; center of higher brain functions Term The three parts of the brain that play a part in embryonic development of the CNS. Name the parts of each. Definition Forebrain (cerebrum and diencephalon); Midbrain (midbrain); Hindbrain (medulla, oblongata, pons, and cerebellum). Term Most of the higher brain functions take place . Definitionwithin the cerebral cortex Term Gray matter is . Definitionunmyelinated neurons Term The outer layer of the cerebrum. How thick is it? Definitioncerebral cortex; 2-4 mm Term The cerebral cortex is divided in to: Definitionthe right and left hemispheres Term The four lobes of the cortex: Definitionfrontal, parietel, temporal, occipital Term The cortex is divided into three general categories by . What are they? Definition Function; sensory areas, motor areas, association areas Term Receive and interpret sensory impulses; mostly posterior to central sulcus Definition Sensory areas Term Control muscle movements; primarily anterior portions of two himispheres Definition Motor areas Term Memory, emotions, resoning, will, judgment...higher brain functions Definition Associated Areas Term The sensory areas receive and interpret sensory impluses; mostley to the . Definitionposterior; central sulcus Term Motor areas control muscle movements; primarily where? Definitionanterior portions of two hemispheres Term The primary motor cortex is part of what lobe? Where is it located? What is it's function? Definition Frontal; precentral gyrus in the frontal lobe; voluntary contractions of specific muscles Term The motor association cortex is part of what lobe? Where is it located and what is its function? Definition Frontal; anterior to primary motor area; communicate with the primary motor area and other regions of the brain (thalamus, etc); controls learned, complex skilled movements and serves as a memory bank for those skills. Term Where is the Motor speech cortex located and what is its function? What is its nickname? Definitionfrontal lobe-one side only usually left; production of speech (motor area); broca's area Term The translation of speech into thought and thought into speech involves integration of : Definitionall language areas and hearing primary and association areas. Term Where is the primary somatosensory area located and what is its function? Definitionpost central gyrus in the parietal lobe; receives sensory impulses from receptors for pain, touch, temperature, and proprioception Term Where you are in space Definitionpropriocepetion Term Where is the primary visual cortex located, what is its function, and what is its nickname? Definitionmedial portion of occipital lobe; receives impules from the thalamic nuclei after the area has synapsed with optic nerves; information received on color, shape, and movement of visual stimuli; visual cortex Term Where is the visual association area located and what is its function? Definitionoccipital lobe, anterior to primary area; receives sensory impulses from primary visual area and evaluates what is seen and compares to past experience Term Where is the primary auditory cortex located and what is its function? Definitionsuperior portion of temporal lobe; interprets basic characteristics of sound: pitch and rhythm Term What areas are located in the frontal lobe? parietal lobe? occipital lobe? temporal lobe? Definitionprimary motor cortex, motor assocation cortex, motor speech cortex; primary somatosensory area; primary visual area, visual association area; primary auditory area, Auditory association area Term Where is the auditory assocation area located, what is its function, and what is its nickname? Definitiontemporal lobe; inferior and posterior to primary area one lobe only, usually left; determines if sound is speech, music or noise; receives impulses from primary area; helps translate words into thoughs; wernicke's area Term The cerebral is divided into the: note: most sensory and motor fibers cross at the level of the so that cortical control of the left side is facilitated by the and vise versa. Definitionright and left brain; brain stem; right Term What makes up the diencephalon and where is it located? Definitionthe thalamus and hypothalamus and lateral geniculate nucleus and posterior pituitary; below the cerebrum Term Most of the diencephalon: oval masses of - form of the ; organized into (clusters of within )Definitiontwo; gray matter; wall; 3rd ventricle; nuclei; cell bodies; CNSTerm The Thalamus acts as a for sensory impluses on their way from the spinal cord, cerebellum, brain stem, to the cortex. Crude appreciation for some of the sensations, relies on the centers for interpretation of this sensory information; some rle in . Definitionrelay station; cortical; cognition Term Where is the hypothalamus located, what is it s function and what is it stimulated by? Definitioninferior to the thalamus; major regulator of homeostasis; info from the cerebrum, brain stem, spinal cord, or by the chemical namture of the blood Term Although the hypothalamus makes up less than percent of total brain volue, it has tremendous influence and importance. It influences: and contains centers for : Definition1; many endocrine reflexes, autonomic reflexes, eating, drinking; temperature regulation, control of blood osmolarity, stress, reproduction, growth Term The cerebrum and diencephalon make up the : Definitionforebrain Term The best known hypothalamic pathway is its involvement in mediating the . Sweaty palms, fast heart beat, increased blood pressure, are all mediated by the hypothalamus. Definitionfight or flight response Supporting users have an ad free experience!Tweet "
},
{
"docid": "D312959",
"title": "What lobe of cerebrum contains the primary visual areas that interpret what a person sees?",
"text": "Answers.com Wiki Answers Categories Science Biology Human Anatomy and Physiology Nervous System Brain What lobe of cerebrum contains the primary visual areas that interpret what a person sees? Flag What lobe of cerebrum contains the primary visual areas that interpret what a person sees? Answer by Amaroque Confidence votes 14.1KThe occipital lobe contains the primary visual areas that interpret what a person sees.2 people found this useful Was this answer useful? Yes Somewhat No Kootye 90 Contributions Lobes of cerebrum? The lobes of the Cerebrum are frontal lobe, parietal lobe, occipital lobe and the temporal lobe. Pbandgilly 14 Contributions What lobes are in the cerebrum? The frontal lobe, parietal lobe, temporal lobe, and occipital lobe. What lobe of the cerebrum is responsible for interpreting light image's into vision?occipital lobe. occipital lobe The lobe of the brain that interprets what you see is the? Occipital Lobe Blue 518,948 Contributions In what cerebral lobe is the visual area located? The visual cortex is located in the Occipital lobe . The occipital lobe is the primary area for what?the occipital lobe is the primary vision center - visual information is received through the retinal cells, then passed on to the lateral geniculate bodies of the thalamus, wh Name the lobe that is the primary visual area? The name of the lobe of the cerebral cortex that is primarilyresponsible for the visual area is called the occipital lobe. It isthe visual processing center part of the brain. What lobes contain the visual cortex?occipital lobe!Which cerebral lobe is the visual area? Occipital The primary gustatory area of the cerebrum is in the? Parietal lobe Which brain lobe contains the primary motor area? The posterior portion of the Frontal lobe The area of the cerebrum responsible for the perception of sound lies in the lobe?temporal lobe Answered In Human Anatomy and Physiology Which lobe of the cerebrum receives and interprets nerve impulses from sensory receptors? Parietal lobe Answered In Muscular System What lobe contains the primary motor area that controls skeletal muscles? Frontal lobe Answered In Human Anatomy and Physiology What lobe contains the primary motor area that controls voluntary movements?the right frontal lobe!Answered In Uncategorized What lobe of the cerebrum would you find the primary auditory area? Temporal Lobe Answered In Uncategorized What is the lobe that contains the primary visual cortex?temporal? "
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ect is a treatment that is used for
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rice-water stools are associated with disease caused by which organism?
| [{"docid":"D213890","title":"Cholera","text":"From Wikipedia, the free encyclopedianavigation search(...TRUNCATED)
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the abo blood types are examples of
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the vitamin that prevents beriberi is
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what temperature should you reheat lasagna to
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both dna and rna are polymers that are made up of
| [{"docid":"D69114","title":"Nucleic acid","text":"From Wikipedia, the free encyclopedianavigation se(...TRUNCATED)
| [{"docid":"D69114","title":"What is RNA and DNA Structure and Function?","text":"What is RNA and DNA(...TRUNCATED)
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contextual spoken language understanding
| [{"docid":"D1350520","title":"Context (language use)","text":"In semiotics, linguistics, sociology a(...TRUNCATED)
| [{"docid":"D1350520","title":"Language development","text":"From Wikipedia, the free encyclopedianav(...TRUNCATED)
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dosimetry medical definition
| [{"docid":"D304123","title":"What Is Medical Dosimetry?","text":"What Is Medical Dosimetry? If you w(...TRUNCATED)
| [{"docid":"D304123","title":"What Is Medical Dosimetry?","text":"What Is Medical Dosimetry? If you w(...TRUNCATED)
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is a unit price item for
| [{"docid":"D1439360","title":".","text":"Error. Page cannot be displayed. Please contact your servic(...TRUNCATED)
| [{"docid":"D1439360","title":"Released product details (form) [AX 2012]","text":"Released product de(...TRUNCATED)
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