Visual Cortex

Functional organization

The primary education visual cortex constitutes the point entrance in the visual cortex of the visual informations coming from the side geniculate Corps of the Thalamus. This area located on the inner face of both hemisphere, around the Scissure calcharine is also called primary visual surface or V1 or, because of their appearance to the Microscope, surface striated. This area has a retinotopic organization : the data coming from the center of the field of vision (in the Fovea) are processed by the occipital part of the surface V1 and those coming from the periphery of the field of vision are treated by the rostrale part. Moreover, just like for the sensitive Homoncule, the foveal area where the vision is the best is surreprésentée compared to the outlying areas.

The data once processed by the primary education visual cortex are transferred towards the surfaces known as extrastriées where thorough treatments will take place. Information in fact will be separated in two distinct ways beyond the V2 surface:

the way ventral , known as also the " what sees? " in which information of form and colors is analyzed in order to lead to a recognition of the present objects in the visual scene.
the way dorsal , known as also the " sees Where? " in which the related informations with the movement and the positions in space are analyzed in order to allow the movements in direction or not objects present (Saccade occulaire, movement of gripping,…)

Neurological plasticity

The cortical visual system shows, following the example other cortical structures, a great plasticity. Thus, at the time of a selective attack of the field of vision (spot plugs), the neuronal surface corresponding to the lesion is reduced gradually to the profit of the close retinal cells: the not stimulated neurons are connected to the close neurons, which causes “to mask” the deficit.

Recent experiments undertaken in the new-born hamster also state that the auditive Cortex can replace the visual Cortex in the event of absence (embryonic) of this last.

Bonds

Internal bonds

Vision

External bonds

the brain on all the levels : The vision
ERTé ACCESS of INRP: The vision

Ventral The stream begins with V1, goes through Visual area V2, then through Visual area V4, and to the temporal Inferior lobe. Ventral The stream, sometimes called the " What Pathway" , is associated with form recognition and object representation. It is also associated with storage off Length-term memory.

Dorsal The stream begins with V1, goes through Visual area V2, then to Visual area V3, Visual area MT (also known ace V5) and to the parietal Inferior lobule. Dorsal The stream, sometimes called the " Where Pathway" however the " How Pathway" , is associated with motion, representation off object hirings, and control off the eyes and arms, especially when visual information is used to guide Jerk S gold reaching.

The dichotomy off the dorsal/ventral pathways (also called the " what/where" however " action/perception" streams) was proposed (among others) by Goodale and Milner (1992) and is still contentious among vision scientists and psychologists. It is probably year over-simplification off the true state off affairs in visual cortex. It is based one the findings that visual illusions such ace the Ebbinghaus illusion may distort judgments off has perceptual natural, goal when the subject responds with year action, such ace grasping, No distortion occurs. However, recent work (Franz et al., 2005) suggests that the both the action and perception systems are equally fooled by such illusions.

Neurons in the visual cortex fire Action potential S when visual stimuli appear within to their Receptive field. With receptive field has small area within the entire visual field. Any given neuron only responds to has off subset stimuli within its receptive field. This property is called tuning . In the earlier visual areas, will neurons cuts simpler tuning. For example, has neuron in V1 may fire to any vertical stimulus in its receptive field. In the higher visual areas, will neurons cuts complex tuning. For example, in the inferior temporal cortex (IT), has neuron may only fire when has certain receptive face appears in its field.

The visual cortex receives its blood supply primarily from the calcarine branch off the cerebral Posterior artery.

Primary visual cortex (V1)

The primary visual cortex is the best studied visual area in the Brain. It is the share off the Cerebral responsible cortex that is for processing visual stimuli. It is the simplest, earliest cortical visual area. It is highly specialized for processing information butt static and moving objects and is excel 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 Striated Gennari off, has distinctive stripe visible to the naked eye that represents Myelin ated Axons from the Lateral geniculate body terminating in bush-hammering 4 off the Gray matter.

Primary The visual cortices is divided into six functionally distinct layers, labelled 1 through 6. To bush-hammer 4, which receives most visual Side input from the geniculate nucleus (LGN), is further divided into 4 layers, labelled 4A, 4B, 4Cα, and 4Cβ. Sublamina 4Cα receives most Magnocellular input from the LGN, while to bush-hammer 4Cβ receives input from Parvocellular pathway S.

Function

V1 has off very well-defined map the space information in vision. For example, in humans the upper bank off the Calcarine sulcus responds strongly to the lower half off Visual field (below the center), and the lower bank off the calcarine to the upper half off visual field. Conceptually, this Retinotopy mapping has transformation off the visual image from Retina to V1. The correspondence between has given subjective hiring in V1 and in the visual field is very precise: even the blind spots are mapped into V1. Evolutionally, this correspondence is very BASIC and found in most animals that possess has V1. In human and animals with has Fovea in the retina, has off broad portion V1 is mapped to the small, central portion off visual field, has phenomenon known ace Cortical magnification. Space Perhaps for the purpose off accurate encoding, will neurons in V1 cuts the smallest off receptive field size any visual cortex areas.

Individual V1 will neurons cuts strong tuning to has small set off stimuli. That is, the neuronal responses edge discriminate small exchanges in visual orientations, space Frequencies and Color S. Furthermore, individual V1 will neurons in human and animals with binocular vision cuts ocular predominance, namely tuning to one off the two eyes. In V1, and primary sensory cortex in general, will neurons with similar tuning properties tightens to cluster together cortical ace columns. David Hubel and Torsten Wiesel proposed the classic ice-cubic organization model off cortical columns for two tuning properties: ocular predominance and orientation. However, this model boat accommodate the color, space frequency and many other features to which will neurons are tuned. Exact The organization off all thesis cortical columns within V1 remains has hot topic off current research.

Current consensus seems to Be that V1 consists off tiled sets off selective spatiotemporal filters. In the space domain, the functioning off V1 edge Be thought off local ace similar to many spatially, complex Fourier transform S. Theoretically, thesis filters together edge neuronal curry out processing off space frequency, orientation, motion, direction, speed (thus temporal frequency), and many other spatiotemporal features. Experiments off V1 will neurons substantiate thesis theories, goal also raise new questions.

The visual information relayed to V1 is not coded in terms off space (gold optical) imagery, goal rather local ace the contrast. Ace year example, for year 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 will neurons code the brightness information (black gold white per). Subsequent ace information is further relayed to visual areas, it is coded ace increasingly not-room frequency/phase signals. Importantly, At thesis early training courses off cortical visual processing, space hiring off visual information is well preserved amid the local contrast encoding.

Current research

Research one the primary visual cortex edge involve recording Action potential S from electrodes within the brain off Cat S, Tag S, mice, but Monkeys, but through recording Intrinsic optical signals from animals gold FMRI signals from human and monkey V1.

Recent One discovery butt V1 is that signals measured by broad FMRI show very attentional modulation. This result strongly contrasts with macaque physiology research showing very small exchanges (gold No exchanges) in firing associated with attentional modulation.

Other current work one V1 seeks to fully characterize its tuning properties, and to uses it ace has model area for the canonical cortical circuit.

Lesions to primary visual cortex usually lead to has Scotoma, but hole in the visual field. Interestingly, patient with scotomas are often whitebait to make uses visual information presented to off to their scotomas, despite being unable to consciously perceive it. This phenomenon, called Blindsight, is widely studied by scientists interested in the neural correlate off Consciousness.

V2

Visual area V2 is the second major area in the visual cortex, and first area within the visual association area. Receives It strong Feedforward connections from V1 and sends strong connections to V3, V4, and V5. It also sends strong Feedback connections to the V1.

Anatomically, V2 is Split into furnace quadrants, has Dorsal and Ventral representation in the left and the right hemispheres. Together thesis furnace areas provide has supplements map off the visual world. Functionally, V2 has many properties in common with V1. Concealments simple properties such ace orientation, space are tuned to frequency, and color. The responses off many V2 will neurons are also modulated by more complex properties, such ace the orientation off illusory contours and whether the stimulus is share off the figure gold the ground (Qiu and von der Heydt, 2005).

Recent research has shown that V2 concealments show has small amount off attentional modulation (more than V1, less than V4), are tuned for moderately complex patterns, and may multiple Be driven by orientations different At subregions within has individual receptive field.

V3

Visual area V3 has off share the dorsal stream, receiving inputs from V2 and primary visual areas. It projects to the posterior Parietal cortex. It may Be anatomically located in Brodmann area 19. Debate exists ace to whether there adjacent are also areas 3A and 3B. Recent work with fMRI has suggested that area V3/V3A may play has role in the processing off total motion (Braddick, 2001).

V4

Visual area V4 is one off the visual areas in the Extrastriate visual cortex off the Macaque monkey. It is located anterior to V2 and posterior to Visual area PIT. It included/understood At least furnace areas (left and right V4d, left and right V4v), and nap groups caudal carryforward that it contains rostral and subdivisions ace well. It is unknown what the human homologous off V4 is, and this resulting is currently the subject off much scrutiny.

Cortical V4 is the third area in the Ventral stream, receiving strong feedforward input from V2 and sending strong connections to the Posterior inferotemporal cortex (PIT). Direct It also receives inputs from V1, especially for central space. In addition, it has weaker connections to V5 and Visual area DP (the dorsal prelunate gyrus).

Ventral V4 is the first area in the stream to show strong Attentional modulation. Most studies indicate that Selective attention edge changes firing spleens in V4 by butt 20%. With seminal paper by Moran and Desimone characterizing thesis effects was the first paper to find attention effects anywhere in the visual cortex (see.

Like V1, V4 is tuned for orientation, space frequency, and color. Unlike V1, it is tuned for object features off intermediate complexity, like simple geometric shapes, although No one has developed has full parametric description off the Tuning space for V4. Visual area V4 is not tuned for complex objects such ace faces, ace areas in the Inferotemporal cortex are.

The firing properties off 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 off V4 was to process color information. Work in the early 1980s proved that V4 was ace directly involved in form recognition ace cortical earlier areas. This research supported the Two Streams hypothesis, first presented by Ungerleider and Mishkin in 1982.

Recent work has shown that V4 exhibits length-term plasticity, encodes stimulus salience, is gated by signals coming from the frontal eye fields, shows exchanges in the space profiles its off receptive fields with attention, and encodes hazard functions.

V5

Visual area V5 , also known ace visual area MT (middle/medial temporal), has area in the extrastriate cortex that appears to process complex visual motion stimuli. It contains many will neurons selective for the motion off complex visual features (line ends, corners). Much work has been carried out one this area local ace it appears to integrate visual motion signals into the total motion off complex objects (Movshon et al., 1985).

Exact There is still much controversy over the form off the computations carried out in area MT (Wilson et al., 1992) and nap research suggests that feature motion is in fact already available At lower levels off the visual system such ace V1 (Tinsley et al., 2003).

Refer

Braddick, agenda, O' Brian, JMD, et al. (2001) Brain areas sensitive to visual motion. Perception, 30,61-72
Franz VH, Scharnowski F, Gegenfurtner (2005) Illusion effects one grasping constant are temporally not dynamic. J Exp Psychol Hum Percept Perform. 31 (6), 1359-78
Goodale & Milner (1992) Separate pathways for perception and action. Trends in Neuroscience, 15,20-25.
Peters, Alan (ED), and Kathleen S. Rockland (ED). 1994. Cerebral Cortex: Primary Visual Cortex in Primates v. 10 (Cerebral Cortex). Kluwer Academic/Plenum Publishers
Peters, Alan (ED) and Bertram Payne (ED). 2001. The Cat Primary Visual Cortex Academic Near.
Moran & Desimone. Selective Attention Spoil Visual Processing in the Extrastriate Cortex. Science 229 (4715), 1985.
Tinsley, C.J., Webb, B.S., Barraclough, N.E., Vincent, C.J., Parker, A., & Derrington, A.M. (2003). Natural The off V1 neural responses to 2D moving patterns depend one receptive-field structure in the marmoset monkey. J Neurophysiol, 90 (2), 930-937.
Qiu FT, von der Heydt R. Figure and ground in the visual cortex: v2 combine stereoscopic cues with gestalt rules. Neuron. 2005 Jul 7; 47 (1): 155-66.
Movshon, J.A., Adelson, E.H., Gizzi, M.S., & Newsome, W.T. (1985). The analysis off moving visual patterns. In: C. Chagass, R. Gattass, & C. Large (Eds.), Pattern recognition mechanisms (pp. 117-151), Rome: The Vatican Near.
Wilson, H.R., Will shoe, V.P., & Yo, C. (1992). With psychophysically motivated model for two-dimensional motion perception. Screw Neurosci, 9 (1), 79-97.

External links

Primary The Visual Cortex by Matthew Schmolesky
Architecture off the Visual Cortex, by David Hubel
For Neuroanatomy off the striate area 17 visit BrainInfo
For Neuroanatomy and Internal Structure off Brodmann area 17 in guenon visit BrainInfo
Histochemical Images off the Visual Cortex
Computational Maps in the Visual Cortex
Simulator for computational modeling off visual cortex maps