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The visual cortex of the
brain A brain is an organ that serves as the center of the nervous system in all vertebrate and most invertebrate animals. It is located in the head, usually close to the sensory organs for senses such as vision. It is the most complex organ in a v ...
is the area of the
cerebral cortex The cerebral cortex, also known as the cerebral mantle, is the outer layer of neural tissue of the cerebrum of the brain in humans and other mammals. The cerebral cortex mostly consists of the six-layered neocortex, with just 10% consisting of ...
that processes visual information. It is located in the
occipital lobe The occipital lobe is one of the four major lobes of the cerebral cortex in the brain of mammals. The name derives from its position at the back of the head, from the Latin ''ob'', "behind", and ''caput'', "head". The occipital lobe is the vi ...
. Sensory input originating from the eyes travels through the
lateral geniculate nucleus In neuroanatomy, the lateral geniculate nucleus (LGN; also called the lateral geniculate body or lateral geniculate complex) is a structure in the thalamus and a key component of the mammalian visual pathway. It is a small, ovoid, ventral projec ...
in the
thalamus The thalamus (from Greek θάλαμος, "chamber") is a large mass of gray matter located in the dorsal part of the diencephalon (a division of the forebrain). Nerve fibers project out of the thalamus to the cerebral cortex in all directions, ...
and then reaches the visual cortex. The area of the visual cortex that receives the sensory input from the lateral geniculate nucleus is the primary visual cortex, also known as visual area 1 ( V1),
Brodmann area A Brodmann area is a region of the cerebral cortex, in the human or other primate brain, defined by its cytoarchitecture, or histological structure and organization of cells. History Brodmann areas were originally defined and numbered by the ...
17, or the striate cortex. The
extrastriate The extrastriate cortex is the region of the occipital lobe, occipital Cerebral cortex, cortex of the mammalian brain located next to the primary visual cortex. Primary visual cortex (V1) is also named striate cortex because of its striped appear ...
areas consist of visual areas 2, 3, 4, and 5 (also known as V2, V3, V4, and V5, or
Brodmann area 18 Human Brodmann area 18, or BA18, is part of the occipital cortex in the human brain. It accounts for the bulk of the volume of the occipital lobe. It is known as a "Visual Association Area" or V2 and is a first stage in processing or feature ext ...
and all
Brodmann area 19 Brodmann area 19, or BA 19, is part of the occipital lobe cortex in the human brain. Along with area 18, it comprises the extrastriate (or peristriate) cortex. In humans with normal sight, extrastriate cortex is a visual association area, with feat ...
). Both hemispheres of the brain include a visual cortex; the visual cortex in the left hemisphere receives signals from the right
visual field The visual field is the "spatial array of visual sensations available to observation in introspectionist psychological experiments". Or simply, visual field can be defined as the entire area that can be seen when an eye is fixed straight at a point ...
, and the visual cortex in the right hemisphere receives signals from the left visual field.


Introduction

The primary visual cortex (V1) is located in and around the
calcarine fissure The calcarine sulcus (or calcarine fissure) is an anatomical landmark located at the caudal end of the medial surface of the brain of humans and other primates. Its name comes from the Latin "calcar" meaning "spur". It is very deep, and known as ...
in the
occipital lobe The occipital lobe is one of the four major lobes of the cerebral cortex in the brain of mammals. The name derives from its position at the back of the head, from the Latin ''ob'', "behind", and ''caput'', "head". The occipital lobe is the vi ...
. Each hemisphere's V1 receives information directly from its ipsilateral
lateral geniculate nucleus In neuroanatomy, the lateral geniculate nucleus (LGN; also called the lateral geniculate body or lateral geniculate complex) is a structure in the thalamus and a key component of the mammalian visual pathway. It is a small, ovoid, ventral projec ...
that receives signals from the contralateral visual hemifield.
Neuron A neuron, neurone, or nerve cell is an electrically excitable cell that communicates with other cells via specialized connections called synapses. The neuron is the main component of nervous tissue in all animals except sponges and placozoa. N ...
s in the visual cortex fire
action potential An action potential occurs when the membrane potential of a specific cell location rapidly rises and falls. This depolarization then causes adjacent locations to similarly depolarize. Action potentials occur in several types of animal cells, ...
s when visual stimuli appear within their
receptive field The receptive field, or sensory space, is a delimited medium where some physiological stimuli can evoke a sensory neuronal response in specific organisms. Complexity of the receptive field ranges from the unidimensional chemical structure of od ...
. 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 Neuronal tuning refers to the hypothesized property of brain cells by which they selectively represent a particular type of sensory, association, motor, or cognitive information. Some neuronal responses have been hypothesized to be optimally tuned t ...
''. 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 The posterior cerebral artery (PCA) is one of a pair of cerebral arteries that supply oxygenated blood to the occipital lobe, part of the back of the human brain. The two arteries originate from the distal end of the basilar artery, where it bifur ...
.


Psychological model of the neural processing of visual information


Ventral-dorsal model

V1 transmits information to two primary pathways, called the ventral stream and the dorsal stream. * The
ventral stream The two-streams hypothesis is a model of the neural processing of vision as well as hearing. The hypothesis, given its initial characterisation in a paper by David Milner and Melvyn A. Goodale in 1992, argues that humans possess two distinct visual ...
begins with V1, goes through visual area V2, then through visual area V4, and to the
inferior temporal cortex The inferior temporal gyrus is one of three gyri of the temporal lobe and is located below the middle temporal gyrus, connected behind with the inferior occipital gyrus; it also extends around the infero-lateral border on to the inferior surface o ...
(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 Long-term memory (LTM) is the stage of the Atkinson–Shiffrin memory model in which informative knowledge is held indefinitely. It is defined in contrast to short-term and working memory, which persist for only about 18 to 30 seconds. Long-t ...
. * The
dorsal stream The two-streams hypothesis is a model of the neural processing of vision as well as hearing. The hypothesis, given its initial characterisation in a paper by David Milner and Melvyn A. Goodale in 1992, argues that humans possess two distinct visual ...
begins with V1, goes through Visual area V2, then to the
dorsomedial area The visual cortex of the brain is the area of the cerebral cortex that processes visual perception, visual information. It is located in the occipital lobe. Sensory input originating from the eyes travels through the lateral geniculate nucleus in ...
(DM/V6) and medial temporal area (MT/V5) and to the
posterior parietal cortex The posterior parietal cortex (the portion of parietal neocortex posterior to the primary somatosensory cortex) plays an important role in planned movements, spatial reasoning, and attention. Damage to the posterior parietal cortex can produce a ...
. 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
saccade A saccade ( , French for ''jerk'') is a quick, simultaneous movement of both eyes between two or more phases of fixation in the same direction.Cassin, B. and Solomon, S. ''Dictionary of Eye Terminology''. Gainesville, Florida: Triad Publishi ...
s or reaching. The what vs. where account of the ventral/dorsal pathways was first described by Ungerleider and Mishkin. 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. It has been shown that visual illusions such as the
Ebbinghaus illusion The Ebbinghaus illusion or Titchener circles is an optical illusion of relative size perception. Named for its discoverer, the German psychologist Hermann Ebbinghaus (1850–1909), the illusion was popularized in the English-speaking world by Ed ...
distort judgements of a perceptual nature, but when the subject responds with an action, such as grasping, no distortion occurs. Work such as the one from Franz et al. 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 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.


Primary visual cortex (V1)

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 Pattern recognition is the automated recognition of patterns and regularities in data. It has applications in statistical data analysis, signal processing, image analysis, information retrieval, bioinformatics, data compression, computer graphi ...
. The primary visual cortex, which is defined by its function or stage in the visual system, is approximately equivalent to the striate cortex, also known as Brodmann area 17, which is defined by its anatomical location. The name "striate cortex" is derived from the
line of Gennari The line of Gennari (also called the "band" or "stria" of Gennari) is a band of myelinated axons that runs parallel to the surface of the cerebral cortex on the banks of the calcarine fissure in the occipital lobe. This formation is visible to the ...
, a distinctive stripe visible to the naked eye that represents
myelin Myelin is a lipid-rich material that surrounds nerve cell axons (the nervous system's "wires") to insulate them and increase the rate at which electrical impulses (called action potentials) are passed along the axon. The myelinated axon can be ...
ated
axons An axon (from Greek ἄξων ''áxōn'', axis), or nerve fiber (or nerve fibre: see American and British English spelling differences#-re, -er, spelling differences), is a long, slender projection of a nerve cell, or neuron, in vertebrates, th ...
from the
lateral geniculate body In neuroanatomy, the lateral geniculate nucleus (LGN; also called the lateral geniculate body or lateral geniculate complex) is a structure in the thalamus and a key component of the mammalian visual pathway. It is a small, ovoid, ventral project ...
terminating in layer 4 of the
gray matter Grey matter is a major component of the central nervous system, consisting of neuronal cell bodies, neuropil (dendrites and unmyelinated axons), glial cells (astrocytes and oligodendrocytes), synapses, and capillaries. Grey matter is distinguis ...
. 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 In neuroanatomy, the lateral geniculate nucleus (LGN; also called the lateral geniculate body or lateral geniculate complex) is a structure in the thalamus and a key component of the mammalian visual pathway. It is a small, ovoid, ventral projec ...
(LGN), is further divided into 4 layers, labelled 4A, 4B, 4Cα, and 4Cβ. Sublamina 4Cα receives mostly magnocellular input from the LGN, while layer 4Cβ receives input from parvocellular pathways. The average number of neurons in the adult human primary visual cortex in each hemisphere has been estimated at 140 million.


Function

The first stage of visual processing in the cortex is called V1. V1 has a very well-defined map (''the
retinotopic Retinotopy (from Greek τόπος, place) is the mapping of visual input from the retina to neurons, particularly those neurons within the visual stream. For clarity, 'retinotopy' can be replaced with 'retinal mapping', and 'retinotopic' with 'r ...
map'') of the spatial information in vision. For example, in humans, the upper bank of the
calcarine sulcus The calcarine sulcus (or calcarine fissure) is an anatomical landmark located at the caudal end of the medial surface of the brain of humans and other primates. Its name comes from the Latin "calcar" meaning "spur". It is very deep, and known ...
(in the occipital lobe) responds strongly to the lower half of
visual field The visual field is the "spatial array of visual sensations available to observation in introspectionist psychological experiments". Or simply, visual field can be defined as the entire area that can be seen when an eye is fixed straight at a point ...
(below the center), and the lower bank of the calcarine to the upper half of visual field. In concept, this
retinotopic Retinotopy (from Greek τόπος, place) is the mapping of visual input from the retina to neurons, particularly those neurons within the visual stream. For clarity, 'retinotopy' can be replaced with 'retinal mapping', and 'retinotopic' with 'r ...
mapping is a projection of the visual image from
retina The retina (from la, rete "net") is the innermost, light-sensitive layer of tissue of the eye of most vertebrates and some molluscs. The optics of the eye create a focused two-dimensional image of the visual world on the retina, which then ...
to V1.Johannes Kepler (1604) Paralipomena to Witelo whereby The Optical Part of Astronomy is Treated (Ad Vitellionem Paralipomena, quibus astronomiae pars optica traditvr, 1604), as cited by A.Mark Smith (2015) From Sight to Light. Kepler modeled the eye as a water-filled glass sphere, and discovered that each point of the scene taken in by the eye projects onto a point on the back of the eye (the retina). The correspondence between a given location in V1 and in the subjective visual field is very precise: even the blind spots of the retina 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 Fovea () (Latin for "pit"; plural foveae ) is a term in anatomy. It refers to a pit or depression in a structure. Human anatomy *Fovea centralis of the retina * Fovea buccalis or Dimple * Fovea of the femoral head * Trochlear fovea of the fr ...
(
cones A cone is a three-dimensional geometric shape that tapers smoothly from a flat base (frequently, though not necessarily, circular) to a point called the apex or vertex. A cone is formed by a set of line segments, half-lines, or lines conn ...
in the retina), a large portion of V1 is mapped to the small, central portion of visual field, a phenomenon known as
cortical magnification Cortical magnification describes how many neurons in an area of the visual cortex are 'responsible' for processing a stimulus of a given size, as a function of visual field location. In the center of the visual field, corresponding to the center of ...
. Perhaps for the purpose of accurate spatial encoding, neurons in V1 have the smallest
receptive field The receptive field, or sensory space, is a delimited medium where some physiological stimuli can evoke a sensory neuronal response in specific organisms. Complexity of the receptive field ranges from the unidimensional chemical structure of od ...
size (that is, the highest resolution) 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 ''Orientations'' is a bimonthly print magazine published in Hong Kong and distributed worldwide since 1969. It is an authoritative source of information on the many and varied aspects of the arts of East and Southeast Asia, the Himalayas, the India ...
,
spatial frequencies In mathematics, physics, and engineering, spatial frequency is a characteristic of any structure that is periodic across position in space. The spatial frequency is a measure of how often sinusoidal components (as determined by the Fourier tra ...
and
color Color (American English) or colour (British English) is the visual perceptual property deriving from the spectrum of light interacting with the photoreceptor cells of the eyes. Color categories and physical specifications of color are associ ...
s (as in the optical system of a
camera obscura A camera obscura (; ) is a darkened room with a aperture, small hole or lens at one side through which an image is 3D projection, projected onto a wall or table opposite the hole. ''Camera obscura'' can also refer to analogous constructions su ...
, but projected onto
retina The retina (from la, rete "net") is the innermost, light-sensitive layer of tissue of the eye of most vertebrates and some molluscs. The optics of the eye create a focused two-dimensional image of the visual world on the retina, which then ...
l cells of the eye, which are clustered in density and fineness). Each V1 neuron propagates a signal from a retinal cell, in continuation. Furthermore, individual V1 neurons in humans and animals with
binocular vision In biology, binocular vision is a type of vision in which an animal has two eyes capable of facing the same direction to perceive a single three-dimensional image of its surroundings. Binocular vision does not typically refer to vision where an ...
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 column A cortical column is a group of neurons forming a cylindrical structure through the cerebral cortex of the brain perpendicular to the cortical surface. The structure was first identified by Mountcastle in 1957. He later identified cortical minicolu ...
s.
David Hubel David Hunter Hubel (February 27, 1926 – September 22, 2013) was a Canadian American neurophysiologist noted for his studies of the structure and function of the visual cortex. He was co-recipient with Torsten Wiesel of the 1981 Nobel Priz ...
and
Torsten Wiesel Torsten Nils Wiesel (born 3 June 1924) is a Swedish neurophysiologist. With David H. Hubel, he received the 1981 Nobel Prize in Physiology or Medicine, for their discoveries concerning information processing in the visual system; the prize was s ...
proposed the classic ice-cube organization model of cortical columns for two tuning properties:
ocular dominance Ocular dominance, sometimes called eye preference or eyedness, is the tendency to prefer visual perception, visual input from one eye to the other. It is somewhat analogous to the laterality of right- or left-handedness; however, the side of the d ...
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. The mathematical modeling of this function has been compared to
Gabor transform The Gabor transform, named after Dennis Gabor, is a special case of the short-time Fourier transform. It is used to determine the sinusoidal frequency and phase content of local sections of a signal as it changes over time. The function to be transf ...
s. 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
feedback Feedback occurs when outputs of a system are routed back as inputs as part of a chain of cause-and-effect that forms a circuit or loop. The system can then be said to ''feed back'' into itself. The notion of cause-and-effect has to be handled ...
processing (the influence of higher-tier cortical areas on lower-tier cortical areas) and lateral connections from
pyramidal neurons Pyramidal cells, or pyramidal neurons, are a type of multipolar neuron found in areas of the brain including the cerebral cortex, the hippocampus, and the amygdala. Pyramidal neurons are the primary excitation units of the mammalian prefrontal cor ...
(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 Edge detection includes a variety of mathematical methods that aim at identifying edges, curves in a digital image at which the image brightness changes sharply or, more formally, has discontinuities. The same problem of finding discontinuitie ...
. 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). A theoretical explanation of the computational function of the simple cells in the primary visual cortex has been presented in. It is described how receptive field shapes similar to those found by the biological receptive field measurements performed by DeAngelis et al. can be derived as a consequence of structural properties of the environment in combination with internal consistency requirements to guarantee consistent image representations over multiple spatial and temporal scales. It is also described how the characteristic receptive field shapes, tuned to different scales, orientations and directions in image space, allow the visual system to compute invariant responses under natural image transformations at higher levels in the visual hierarchy. In primates, one role of V1 might be to create a
saliency map In computer vision, a saliency map is an image that highlights the region on which people's eyes focus first. The goal of a saliency map is to reflect the degree of importance of a pixel to the human visual system. For example, in this image, a p ...
(highlights what is important) from visual inputs to guide the shifts of attention known as gaze shifts.Zhaoping, L. 2014, The V1 hypothesis—creating a bottom-up saliency map for pre-attentive selection and segmentation, https://www.oxfordscholarship.com/view/10.1093/acprof:oso/9780199564668.001.0001/acprof-9780199564668-chapter-5. According to the
V1 Saliency Hypothesis The V1 Saliency Hypothesis, or V1SH (pronounced‘vish’) is a theory about V1, the primary visual cortex (V1). It proposes that the V1 in primates creates a saliency map of the visual field to guide visual attention or gaze shifts exogenously. ...
, V1 does this by transforming visual inputs to neural firing rates from millions of neurons, such that the visual location signaled by the highest firing neuron is the most salient location to attract gaze shift. V1's outputs are received by the
superior colliculus In neuroanatomy, the superior colliculus () is a structure lying on the roof of the mammalian midbrain. In non-mammalian vertebrates, the homologous structure is known as the optic tectum, or optic lobe. The adjective form ''tectal'' is commonly ...
(in the mid-brain), among other locations, which reads out the V1 activities to guide gaze shifts. Differences in size of V1 also seem to have an effect on the perception of illusions.


V2

Visual area V2, or secondary visual cortex, also called prestriate cortex, 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 Feedback occurs when outputs of a system are routed back as inputs as part of a chain of cause-and-effect that forms a circuit or loop. The system can then be said to ''feed back'' into itself. The notion of cause-and-effect has to be handled ...
connections to V1. In terms of anatomy, V2 is split into four quadrants, a
dorsal Dorsal (from Latin ''dorsum'' ‘back’) may refer to: * Dorsal (anatomy), an anatomical term of location referring to the back or upper side of an organism or parts of an organism * Dorsal, positioned on top of an aircraft's fuselage * Dorsal co ...
and
ventral Standard anatomical terms of location are used to unambiguously describe the anatomy of animals, including humans. The terms, typically derived from Latin or Greek language, Greek roots, describe something in its standard anatomical position. Th ...
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 color. The responses of many V2 neurons are also modulated by more complex properties, such as the orientation of
illusory contours Illusory contours or subjective contours are visual illusions that evoke the perception of an edge without a luminance or color change across that edge. Illusory brightness and depth ordering often accompany illusory contours. Friedrich Schumann i ...
,
binocular disparity Binocular disparity refers to the difference in image location of an object seen by the left and right human eye, eyes, resulting from the eyes’ horizontal separation (parallax). The brain uses binocular disparity to extract depth information from ...
, and whether the stimulus is part of the figure or the ground. 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. 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). Most of the neurons of this area in primates are tuned to simple visual characteristics such as orientation, spatial frequency, size, color, and shape. 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 one 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.


Third visual cortex, including area V3

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 The parietal lobe is one of the four major lobes of the cerebral cortex in the brain of mammals. The parietal lobe is positioned above the temporal lobe and behind the frontal lobe and central sulcus. The parietal lobe integrates sensory informa ...
. It may be anatomically located in
Brodmann area 19 Brodmann area 19, or BA 19, is part of the occipital lobe cortex in the human brain. Along with area 18, it comprises the extrastriate (or peristriate) cortex. In humans with normal sight, extrastriate cortex is a visual association area, with feat ...
. Braddick using fMRI has suggested that area V3/V3A may play a role in the processing of
global motion Motion perception is the process of inferring the speed and direction of elements in a scene based on visual perception, visual, Vestibular system, vestibular and proprioceptive inputs. Although this process appears straightforward to most observe ...
Other studies prefer to consider dorsal V3 as part of a larger area, named the
dorsomedial area The visual cortex of the brain is the area of the cerebral cortex that processes visual perception, visual information. It is located in the occipital lobe. Sensory input originating from the eyes travels through the lateral geniculate nucleus in ...
(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 The inferior temporal gyrus is one of three gyri of the temporal lobe and is located below the middle temporal gyrus, connected behind with the inferior occipital gyrus; it also extends around the infero-lateral border on to the inferior surface o ...
. 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.


V4

Visual area V4 is one of the visual areas in the
extrastriate The extrastriate cortex is the region of the occipital lobe, occipital Cerebral cortex, cortex of the mammalian brain located next to the primary visual cortex. Primary visual cortex (V1) is also named striate cortex because of its striped appear ...
visual cortex. In
macaques The macaques () constitute a genus (''Macaca'') of sociality, gregarious Old World monkeys of the subfamily Cercopithecinae. The 23 species of macaques inhabit species distribution, ranges throughout Asia, North Africa, and (in barbary 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. V4 is the third cortical area in the
ventral stream The two-streams hypothesis is a model of the neural processing of vision as well as hearing. The hypothesis, given its initial characterisation in a paper by David Milner and Melvyn A. Goodale in 1992, argues that humans possess two distinct visual ...
, 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 The two-streams hypothesis is a model of the neural processing of vision as well as hearing. The hypothesis, given its initial characterisation in a paper by David Milner and Melvyn A. Goodale in 1992, argues that humans possess two distinct visual ...
to show strong attentional modulation. Most studies indicate that
selective attention Attentional control, colloquially referred to as concentration, refers to an individual's capacity to choose what they pay attention to and what they ignore. It is also known as endogenous attention or executive attention. In lay terms, attenti ...
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. 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 The inferior temporal gyrus is one of three gyri of the temporal lobe and is located below the middle temporal gyrus, connected behind with the inferior occipital gyrus; it also extends around the infero-lateral border on to the inferior surface ...
are. The firing properties of V4 were first described by
Semir Zeki Semir Zeki FMedSci FRS is a British and French neurobiologist who has specialised in studying the primate visual brain and more recently the neural correlates of affective states, such as the experience of love, desire and beauty that are ge ...
in the late 1970s, who also named the area. Before that, V4 was known by its anatomical description, the
prelunate gyrus The angular gyrus is a region of the brain lying mainly in the posteroinferior region of the parietal lobe, occupying the posterior part of the inferior parietal lobule. It represents the Brodmann area 39. Its significance is in transferring vi ...
. 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 The two-streams hypothesis is a model of the neural processing of vision as well as hearing. The hypothesis, given its initial characterisation in a paper by David Milner and Melvyn A. Goodale in 1992, argues that humans possess two distinct visu ...
, 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 The frontal eye fields (FEF) are a region located in the frontal cortex, more specifically in Brodmann area 8 or BA8, of the primate brain. In humans, it can be more accurately said to lie in a region around the intersection of the middle fronta ...
, and shows changes in the spatial profile of its receptive fields with attention.


Middle temporal visual area (V5)

The middle temporal visual area (MT or V5) is a region of extrastriate visual cortex. In several species of both
New World monkey New World monkeys are the five families of primates that are found in the tropical regions of Mexico, Central and South America: Callitrichidae, Cebidae, Aotidae, Pitheciidae, and Atelidae. The five families are ranked together as the Ceboidea ( ...
s and
Old World monkey Old World monkey is the common English name for a family of primates known taxonomically as the Cercopithecidae (). Twenty-four genera and 138 species are recognized, making it the largest primate family. Old World monkey genera include baboons ...
s the MT area contains a high concentration of direction-selective neurons. 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 Eye movement includes the voluntary or involuntary movement of the eyes. Eye movements are used by a number of organisms (e.g. primates, rodents, flies, birds, fish, cats, crabs, octopus) to fixate, inspect and track visual objects of inte ...
.


Connections

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 The visual cortex of the brain is the area of the cerebral cortex that processes visual perception, visual information. It is located in the occipital lobe. Sensory input originating from the eyes travels through the lateral geniculate nucleus in ...
), the
koniocellular A koniocellular cell (konio: Greek, ''dust'' or ''poison'', also known as K cell) is a neuron with a small cell body that is located in the koniocellular layer of the lateral geniculate nucleus (LGN) in primates, including humans. Koniocellular la ...
regions of the
LGN In neuroanatomy, the lateral geniculate nucleus (LGN; also called the lateral geniculate body or lateral geniculate complex) is a structure in the thalamus and a key component of the mammalian visual pathway. It is a small, ovoid, Anatomical term ...
, 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 The retrosplenial cortex (RSC) is a cortical area in the brain comprising Brodmann areas 29 and 30. It is secondary association cortex, making connections with numerous other brain regions. The region's name refers to its anatomical location imm ...
. A standard view is that V1 provides the "most important" input to MT. 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. Moreover, research by
Semir Zeki Semir Zeki FMedSci FRS is a British and French neurobiologist who has specialised in studying the primate visual brain and more recently the neural correlates of affective states, such as the experience of love, desire and beauty that are ge ...
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

The first studies of the
electrophysiological Electrophysiology (from Greek , ''ēlektron'', "amber" etymology of "electron"">Electron#Etymology">etymology of "electron" , ''physis'', "nature, origin"; and , ''-logia'') is the branch of physiology that studies the electrical properties of bi ...
properties of neurons in MT showed that a large portion of the cells are tuned to the speed and direction of moving visual stimuli..
Lesion A lesion is any damage or abnormal change in the tissue of an organism, usually caused by disease or trauma. ''Lesion'' is derived from the Latin "injury". Lesions may occur in plants as well as animals. Types There is no designated classifi ...
studies have also supported the role of MT in motion perception and eye movements. 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. 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.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. 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. There is still much controversy over the exact form of the computations carried out in area MT and some research suggests that feature motion is in fact already available at lower levels of the visual system such as V1.


Functional organization

MT was shown to be organized in direction columns. DeAngelis argued that MT neurons were also organized based on their tuning for binocular disparity.


V6

The dorsomedial area (DM) also known as V6, appears to respond to visual stimuli associated with self-motion and wide-field stimulation. V6 is a subdivision of the visual cortex of primates first described by
John Allman John Morgan Allman is an American neuroscientist at the California Institute of Technology in Pasadena, California, active in the fields of primates, cognition and evolutionary neuroscience. Life He graduated from University of Chicago with a Ph ...
and
Jon Kaas Jon Kaas is a professor at Vanderbilt University and a member of the United States National Academy of Sciences. He has made discoveries about the organization of the mammalian brain, including the description of many areas of the cerebral cortex ...
in 1975. V6 is located in the dorsal part of the
extrastriate cortex The extrastriate cortex is the region of the occipital cortex of the mammalian brain located next to the primary visual cortex. Primary visual cortex (V1) is also named striate cortex because of its striped appearance in the microscope. The extra ...
, near the deep groove through the centre of the brain (
medial longitudinal fissure The longitudinal fissure (or cerebral fissure, great longitudinal fissure, median longitudinal fissure, interhemispheric fissure) is the deep groove that separates the two cerebral hemispheres of the vertebrate brain. Lying within it is a continu ...
), and typically also includes portions of the medial cortex, such as the
parieto-occipital sulcus In neuroanatomy, the parieto-occipital sulcus (also called the parieto-occipital fissure) is a deep sulcus in the cerebral cortex that marks the boundary between the cuneus and precuneus, and also between the parietal and occipital lobes. Only ...
(POS). DM contains a topographically organized representation of the entire field of vision. There are similarities between the visual area V5 and V6 of the
common marmoset The common marmoset (''Callithrix jacchus'') also called white-tufted marmoset or white-tufted-ear marmoset is a New World monkey. It originally lived on the northeastern coast of Brazil, in the states of Piaui, Paraiba, Ceará, Rio Grande do No ...
. Both areas receive direct connections from the
primary visual cortex The visual cortex of the brain is the area of the cerebral cortex that processes visual information. It is located in the occipital lobe. Sensory input originating from the eyes travels through the lateral geniculate nucleus in the thalamus and ...
. And both have a high
myelin Myelin is a lipid-rich material that surrounds nerve cell axons (the nervous system's "wires") to insulate them and increase the rate at which electrical impulses (called action potentials) are passed along the axon. The myelinated axon can be ...
content, a characteristic that is usually present in brain structures involved in fast transmission of information. For many years, it was considered that DM only existed in
New World monkeys New World monkeys are the five families of primates that are found in the tropical regions of Mexico, Central and South America: Callitrichidae, Cebidae, Aotidae, Pitheciidae, and Atelidae. The five families are ranked together as the Ceboidea ( ...
. However, more recent research has suggested that DM also exists in
Old World monkeys Old World monkey is the common English name for a family of primates known taxonomically as the Cercopithecidae (). Twenty-four genera and 138 species are recognized, making it the largest primate family. Old World monkey genera include baboons ...
and humans. V6 is also sometimes referred to as the parieto-occipital area (PO), although the correspondence is not exact.


Properties

Neurons in area DM/V6 of
night monkey Night monkeys, also known as owl monkeys or douroucoulis (), are nocturnal New World monkeys of the genus ''Aotus'', the only member of the family Aotidae (). The genus comprises eleven species which are found across Panama and much of South Ame ...
s and
common marmoset The common marmoset (''Callithrix jacchus'') also called white-tufted marmoset or white-tufted-ear marmoset is a New World monkey. It originally lived on the northeastern coast of Brazil, in the states of Piaui, Paraiba, Ceará, Rio Grande do No ...
s 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. However, in comparison with area MT, a much smaller proportion of DM cells shows selectivity for the direction of motion of visual patterns. 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. 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. 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.


Pathways

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 The two-streams hypothesis is a model of the neural processing of vision as well as hearing. The hypothesis, given its initial characterisation in a paper by David Milner and Melvyn A. Goodale in 1992, argues that humans possess two distinct visual ...
", referred to by some as the "dorsomedial pathway". This pathway is likely to be important for the control of skeletomotor activity, including postural reactions and reaching movements towards objects The main 'feedforward' connection of DM is to the cortex immediately rostral to it, in the interface between the occipital and parietal lobes (V6A). This region has, in turn, relatively direct connections with the regions of the frontal lobe that control arm movements, including the
premotor cortex The premotor cortex is an area of the motor cortex lying within the frontal lobe of the brain just anterior to the primary motor cortex. It occupies part of Brodmann's area 6. It has been studied mainly in primates, including monkeys and humans. ...
.


See also

*
Cortical area The cerebral cortex, also known as the cerebral mantle, is the outer layer of neural tissue of the cerebrum of the brain in humans and other mammals. The cerebral cortex mostly consists of the six-layered neocortex, with just 10% consisting of ...
*
Cortical blindness Cortical blindness is the total or partial loss of vision in a normal-appearing eye caused by damage to the brain's occipital cortex. Cortical blindness can be acquired or congenital, and may also be transient in certain instances. Acquired cortic ...
*
Feature integration theory Feature integration theory is a theory of attention developed in 1980 by Anne Treisman and Garry Gelade that suggests that when perceiving a stimulus, features are "registered early, automatically, and in parallel, while objects are identified separ ...
*
List of regions in the human brain The human brain anatomical regions are ordered following standard neuroanatomy hierarchies. Functional, connective, and developmental regions are listed in parentheses where appropriate. Hindbrain (rhombencephalon) Myelencephalon * Med ...
*
Retinotopy Retinotopy (from Greek τόπος, place) is the mapping of visual input from the retina to neurons, particularly those neurons within the visual stream. For clarity, 'retinotopy' can be replaced with 'retinal mapping', and 'retinotopic' with 'r ...
*
Visual processing Visual processing is a term that is used to refer to the brain's ability to use and interpret visual information from the world around us. The process of converting light energy into a meaningful image is a complex process that is facilitated by ...
*
Complex cell Complex cells can be found in the primary visual cortex (V1), the secondary visual cortex (V2), and Brodmann area 19 ( V3). Like a simple cell, a complex cell will respond primarily to oriented edges and gratings, however it has a degree of spa ...


References


External links


The Primary Visual Cortex by Matthew Schmolesky
at
University of Utah The University of Utah (U of U, UofU, or simply The U) is a public research university in Salt Lake City, Utah. It is the flagship institution of the Utah System of Higher Education. The university was established in 1850 as the University of De ...

Architecture of the Visual Cortex, by David Hubel
at
Harvard University Harvard University is a private Ivy League research university in Cambridge, Massachusetts. Founded in 1636 as Harvard College and named for its first benefactor, the Puritan clergyman John Harvard, it is the oldest institution of higher le ...
* – striate area 17 * – Brodmann area 17 in guenon *
Simulator for computational modeling of visual cortex maps
at topographica.org {{DEFAULTSORT:Visual Cortex Visual perception