Transformation of visual signals in the lateral (outer) geniculate body. Outer geniculate body Outer geniculate body

Lateral geniculate body

Lateral geniculate body(extrinsic geniculate body, LC) is an easily recognizable brain structure that is placed on the lower lateral side of the thalamic cushion in the form of a fairly large flat tubercle. In the LCT of primates and humans, six layers are morphologically defined: 1 and 2 - layers of large cells (magnocellular), 3-6 - layers of small cells (parvocellular). Layers 1, 4 and 6 receive afferents from the contralateral (located in the hemisphere opposite to the LCT) eye, and layers 2, 3 and 5 from the ipsilateral (located in the same hemisphere as the LCT).

Schematic diagram of LKT primates. Layers 1 and 2 are located more ventrally, closer to the incoming fibers of the optical path.

The number of LCT layers involved in signal processing from retinal ganglion cells varies depending on the retinal eccentricity:

- when the eccentricity is less than 1º, two parvocellular layers are involved in the processing;
- from 1º to 12º (eccentricity of a blind spot) - all six layers;
- from 12º to 50º - four layers;
- from 50º - two layers connected with the contralateral eye

There are no binocular neurons in the LCT of primates. They appear only in the primary visual cortex.

Literature

Hubel D. Eye, brain, vision / D. Hubel; Per. from English. O. V. Levashova and G. A. Sharaeva.- M.: "Mir", 1990.- 239 p.
Morphology of the nervous system: Proc. allowance / D. K. Obukhov, N. G. Andreeva, G. P. Demyanenko and others; Rep. ed. V. P. Babmindra. - L.: Nauka, 1985. - 161 p.
Erwin E. Relationship between laminar topology and retinotopy in the rhesus lateral geniculate nucleus: results from a functional atlas / E. Erwin, F.H. Baker, W.F. Busen et al. // Journal of Comparative Neurology.- 1999.- Vol.407, No. 1.- P.92-102.

Wikimedia Foundation. 2010 .

Abqaik (oil field)
75th Ranger Regiment

See what the "Lateral geniculate body" is in other dictionaries:

Lateral geniculate body- two cell nuclei of the thalamus, located at the ends of each of the optical tracts. Paths from the left side of the left and right retinas approach the left body, to the right, respectively, the right side of the retina. From here, the visual paths are directed to ... ... Encyclopedic Dictionary of Psychology and Pedagogy

Lateral geniculate body (LKT)- The main sensory center of vision, located in the thalamus, a part of the brain that plays the role of the main switching device in relation to incoming sensory information. Axons originating from the LCT enter the visual zone of the occipital lobe of the cortex ... Psychology of sensations: a glossary

geniculate body lateral- (c. g. laterale, PNA, BNA, JNA) K. t., lying on the lower surface of the thalamus laterally from the handle of the superior colliculus of the quadrigemina: the location of the subcortical center of vision ... Big Medical Dictionary

visual system- Pathways of the visual analyzer 1 Left half of the visual field, 2 Right half of the visual field, 3 Eye, 4 Retina, 5 Optic nerves, 6 Eye ... Wikipedia

brain structures- Human brain reconstruction based on MRI Contents 1 Brain 1.1 Prosencephalon (forebrain) ... Wikipedia

visual perception

Vision- Pathways of the visual analyzer 1 Left half of the visual field, 2 Right half of the visual field, 3 Eye, 4 Retina, 5 Optic nerves, 6 Oculomotor nerve, 7 Chiasma, 8 Optic tract, 9 Lateral geniculate body, 10 ... ... Wikipedia

Viewer- Pathways of the visual analyzer 1 Left half of the visual field, 2 Right half of the visual field, 3 Eye, 4 Retina, 5 Optic nerves, 6 Oculomotor nerve, 7 Chiasma, 8 Optic tract, 9 Lateral geniculate body, 10 ... ... Wikipedia

human visual system- Pathways of the visual analyzer 1 Left half of the visual field, 2 Right half of the visual field, 3 Eye, 4 Retina, 5 Optic nerves, 6 Oculomotor nerve, 7 Chiasma, 8 Optic tract, 9 Lateral geniculate body, 10 ... ... Wikipedia

visual analyzer- Pathways of the visual analyzer 1 Left half of the visual field, 2 Right half of the visual field, 3 Eye, 4 Retina, 5 Optic nerves, 6 Oculomotor nerve, 7 Chiasma, 8 Optic tract, 9 Lateral geniculate body, 10 ... ... Wikipedia

represents a small oblong elevation at the posterior-lower end of the visual mound on the side of the pulvinar. At the ganglion cells of the external geniculate body, the fibers of the optic tract end and the fibers of the Graziole bundle originate from them. Thus, the peripheral neuron ends here and the central neuron of the optic pathway originates.

It has been established that although most of the fibers of the optic tract end in the lateral geniculate body, still a small part of them goes to the pulvinar and anterior quadrigemina. These anatomical data formed the basis for a long-held opinion, according to which both the lateral geniculate body and the pulvinar and anterior quadrigemina were considered primary visual centers.

At present, a lot of data has accumulated that does not allow us to consider the pulvinar and the anterior quadrigemina as primary visual centers.

A comparison of clinical and pathoanatomical data, as well as embryological and comparative anatomy data, does not allow us to attribute the role of the primary visual center to pulvinar. So, according to Genshen's observations, in the presence of pathological changes in the pulvinar field of view remains normal. Brouwer notes that with an altered lateral geniculate body and an unchanged pulvinar, homonymous hemianopsia is observed; with changes in the pulvinar and unchanged lateral geniculate body, the visual field remains normal.

The same is true with anterior quadrigemina. The fibers of the optic tract form the visual layer in it and end in cell groups located near this layer. However, Pribytkov's experiments showed that enucleation of one eye in animals is not accompanied by degeneration of these fibers.

Based on all of the above, there is currently reason to believe that only the lateral geniculate body is the primary visual center.

Turning to the question of the projection of the retina in the lateral geniculate body, the following should be noted. Monakov in general denied the presence of any projection of the retina in the lateral geniculate body. He believed that all fibers coming from different parts of the retina, including papillomacular ones, are evenly distributed throughout the entire external geniculate body. Genshen back in the 90s of the last century proved the fallacy of this view. In 2 patients with homonymous lower quadrant hemianopsia, a post-mortem examination revealed limited changes in the dorsal part of the lateral geniculate body.

Ronne (Ronne) with atrophy of the optic nerves with central scotomas due to alcohol intoxication found limited changes in ganglion cells in the lateral geniculate body, indicating that the area of the macula is projected onto the dorsal part of the geniculate body.

The above observations unequivocally prove the presence of a certain projection of the retina in the external geniculate body. But the clinical and anatomical observations available in this regard are too few and do not yet give an accurate idea of the nature of this projection. The experimental studies of Brouwer and Zeman on monkeys, which we have mentioned, made it possible to study to some extent the projection of the retina in the lateral geniculate body. They found that most of the lateral geniculate body is occupied by the projection of the retinal regions involved in the binocular act of vision. The extreme periphery of the nasal half of the retina, corresponding to the monocularly perceived temporal crescent, is projected onto a narrow zone in the ventral part of the lateral geniculate body. The projection of the macula occupies a large area in the dorsal part. The upper quadrants of the retina project onto the lateral geniculate body ventro-medially; lower quadrants - ventro-laterally. The projection of the retina in the lateral geniculate body in a monkey is shown in Fig. 8.

In the outer geniculate body (Fig. 9)

Rice. nine. The structure of the external geniculate body (according to Pfeifer).

there is also a separate projection of crossed and non-crossed fibers. The studies of M. Minkowski make a significant contribution to the clarification of this issue. He established that in a number of animals after enucleation of one eye, as well as in humans with prolonged unilateral blindness, there are observed in the external geniculate body optic nerve fiber atrophy and ganglion cell atrophy. At the same time, Minkowski discovered a characteristic feature: in both geniculate bodies, atrophy with a certain regularity spreads to different layers of ganglion cells. In the lateral geniculate body of each side, layers with atrophied ganglion cells alternate with layers in which the cells remain normal. Atrophic layers on the side of enucleation correspond to identical layers on the opposite side, which remain normal. At the same time, similar layers, which remain normal on the side of enucleation, atrophy on the opposite side. Thus, the atrophy of the cell layers in the lateral geniculate body that occurs after the enucleation of one eye is definitely alternating in nature. Based on his observations, Minkowski came to the conclusion that each eye has a separate representation in the lateral geniculate body. Crossed and non-crossed fibers thus terminate at different ganglion cell layers, as is well illustrated in Le Gros Clark's diagram (Fig. 10).

Rice. 10. Scheme of the end of the fibers of the optic tract and the beginning of the fibers of the Graziola bundle in the lateral geniculate body (according to Le Gros Clark).
Solid lines are crossed fibers, dashed lines are non-crossed fibers. 1 - visual tract; 2 - external geniculate body 3 - Graziola bundle; 4 - cortex of the occipital lobe.

Minkowski's data were later confirmed by experimental and clinical and anatomical studies by other authors. L. Ya. Pines and I. E. Prigonnikov examined the lateral geniculate body 3.5 months after enucleation of one eye. At the same time, degenerative changes were noted in the ganglion cells of the central layers in the lateral geniculate body on the side of enucleation, while the peripheral layers remained normal. In the opposite side of the lateral geniculate body, inverse relationships were observed: the central layers remained normal, while degenerative changes were noted in the peripheral layers.

Interesting observations related to the case unilateral blindness long ago, was recently published by the Czechoslovak scientist F. Vrabeg. A 50-year-old patient had one eye removed at the age of ten. Postmortem examination of the lateral geniculate bodies confirmed the presence of alternating degeneration of ganglion cells.

Based on the data presented, it can be considered established that both eyes have a separate representation in the lateral geniculate body and, therefore, crossed and non-crossed fibers end in different layers of ganglion cells.

Retinal ganglion cells project their processes into the lateral geniculate body, where they form a retinotopic map. In mammals, the lateral geniculate body consists of 6 layers, each of which is innervated by either one or the other eye and receives a signal from different subtypes of ganglion cells, forming layers of large cell (magnocellular), small cell (parvocellular) and koniocellular (koniocellular) neurons. The neurons of the lateral geniculate body have center-background receptive fields, similar to retinal ganglion cells.

Neurons of the lateral geniculate body project and form a retinotopic map in the primary visual cortex V 1 , also called "area 17" or striate cortex (striatecortex). The receptive fields of cortical cells, instead of the already familiar organization of receptive fields according to the “center-background” type, consist of lines, or edges, which is a fundamentally new step in the analysis of visual information. The six layers of V 1 have structural features: afferent fibers from the geniculate body terminate mainly in layer 4 (and some in layer 6); cells in layers 2, 3, and 5 receive signals from cortical neurons. The cells of layers 5 and b project processes into the subcortical regions, and the cells of layers 2 and 3 project into other cortical zones. Each vertical column of cells functions as a module, receiving an initial visual signal from a specific location in space and sending processed visual information to secondary visual zones. The columnar organization of the visual cortex is obvious, since the localization of receptive fields remains the same throughout the entire depth of the cortex, and visual information from each eye (right or left) is always processed in strictly defined columns.

Two classes of neurons in region V 1 have been described that differ in their physiological properties. The receptive fields of simple cells are elongated and contain conjugated "on" and "off" "zones. Therefore, the most optimal stimulus for a simple cell is specially oriented beams of light or shadow. A complex cell responds to a certain oriented strip of light; this strip can be located in any area of the receptive field.The inhibition of simple or complex cells resulting from image recognition carries even more detailed information about the properties of the signal, such as the presence of a line of a certain length or a certain angle within a given receptive field.

The receptive fields of a simple cell are formed as a result of the convergence of a significant number of afferents from the geniculate body. The centers of several receptive fields adjacent to each other form one cortical receptive zone. The field of a complex cell depends on the signals of a simple cell and other cortical cells. The successive change in the organization of receptive fields from the retina to the lateral geniculate body and then to simple and complex cortical cells speaks of a hierarchy in information processing, whereby a number of neural structures of one level are integrated into the next, where an even more abstract concept is formed based on the initial information. At all levels of the visual analyzer, special attention is paid to contrast and definition of image boundaries, and not to the general illumination of the eye. Thus, the complex cells of the visual cortex can "see" the lines that are the boundaries of the rectangle, and they care little about the absolute intensity of the light inside this rectangle. A series of clear and continuous research into the mechanisms of perception of visual information, begun by the pioneering work of Kuffler with the retina, was continued at the level of the visual cortex by Hubel and Wiesel. Hubel gave a vivid description of early experiments on the visual cortex in Stephen Kuffler's laboratory at Johns Hopkins University (USA) in the 1950s. Since then, our understanding of the physiology and anatomy of the cerebral cortex has evolved significantly due to the experiments of Hubel and Wiesel, and also due to a large number of works for which their research was a starting point or source of inspiration. Our goal is to provide a concise, narrative description of signal coding and cortical architecture from a perceptual perspective, based on the classic work of Hubel and Wiesel, as well as more recent experiments by them, their colleagues, and many others. In this chapter, we will only give a schematic sketch of the functional architecture of the lateral geniculate body and the visual cortex, and their role in providing the first steps in the analysis of visual siena: the definition of lines and shapes based on the center-background signal coming from the retina.

When moving from the retina to the lateral geniculate body, and then to the cortex of the hemispheres, questions arise that are beyond the scope of technology. For a long time, it was generally accepted that to understand the functioning of any part of the nervous system, knowledge of the properties of its component neurons is necessary: how they conduct signals and carry information, how they transmit the received information from one cell to another through synapses. However, monitoring the activity of only one individual cell can hardly be an effective method for studying higher functions, where a large number of neurons are involved. The argument that has been used here and continues to be used from time to time is that the brain contains about 10 10 or more cells. Even the simplest task or event involves hundreds of thousands of nerve cells located in various parts of the nervous system. What are the chances of a physiologist to be able to penetrate into the essence of the mechanism of formation of a complex action in the brain, if he can simultaneously examine only one or several nerve cells, a hopelessly small fraction of the total?

Upon closer examination, the logic of such arguments regarding the main complexity of the study associated with a large number of cells and complex higher functions no longer seems so flawless. As is often the case, a simplifying principle emerges that opens up a new and clearer view of the problem. The situation in the visual cortex is simplified by the fact that the main cell types are located separately from each other, in the form of well-organized and repetitive units. This repetitive pattern of neural tissue is closely intertwined with the retinotopic map of the visual cortex. Thus, neighboring points of the retina are projected onto neighboring points on the surface of the visual cortex. This means that the visual cortex is organized in such a way that for each smallest segment of the visual field there is a set of neurons for analyzing information and transmitting it. In addition, using methods that make it possible to isolate functionally related cellular ensembles, patterns of cortical organization of a higher level were identified. Indeed, the architecture of the cortex determines the structural basis of cortical function, so new anatomical approaches inspire new analytical research. Thus, before we describe the functional connections of the visual neurons, it is useful to briefly summarize the general structure of the central visual pathways that originate from the nuclei of the lateral geniculate body.

Lateral geniculate body

The optic nerve fibers start from each eye and end on the cells of the right and left lateral geniculate body (LCT) (Fig. 1), which has a clearly distinguishable layered structure (“geniculate” - geniculate - means “curved like a knee”). In the LCT of a cat, three distinct, well-defined cell layers (A, A 1 , C) can be seen, one of which (A 1) has a complex structure and is further subdivided. In monkeys and other primates, including

human, LKT has six layers of cells. Cells in deeper layers 1 and 2 are larger than in layers 3, 4, 5 and 6, which is why these layers are called large-celled (M, magnocellular) and small-celled (P, parvocellular), respectively. The classification also correlates with large (M) and small (P) retinal ganglion cells, which send their outgrowths to the LCT. Between each M and P layers lies a zone of very small cells: the intralaminar, or koniocellular (K, koniocellular) layer. Layer K cells differ from M and P cells in their functional and neurochemical properties, forming a third channel of information to the visual cortex.

In both the cat and the monkey, each layer of the LCT receives signals from either one eye or the other. In monkeys, layers 6, 4, and 1 receive information from the contralateral eye, while layers 5, 3, and 2 receive information from the ipsilateral eye. The separation of the course of nerve endings from each eye into different layers has been shown using electrophysiological and a number of anatomical methods. Particularly surprising is the type of branching of an individual fiber of the optic nerve when horseradish peroxidase is injected into it (Fig. 2).

The formation of terminals is limited to the layers of the LCT for this eye, without going beyond the boundaries of these layers. Due to the systematic and specific division of the optic nerve fibers in the region of the chiasm, all the receptive fields of the LCT cells are located in the visual field of the opposite side.

Rice. 2. Endings of the optic nerve fibers in the LCT of a cat. Horseradish peroxidase was injected into one of the axons from the zone with the "on" center of the contralateral eye. Axon branches end on cells of layers A and C, but not A 1 .

Rice. 3. Receptive fields of ST cells. The concentric receptive fields of the LCT cells resemble the fields of ganglion cells in the retina, dividing into fields with "on" and "off" centers. The responses of the cell with the "on" center of the LCT of a cat are shown. The bar above the signal shows the duration of illumination. Central and peripheral the zones offset each other's effects, so diffuse illumination of the entire receptive field gives only weak responses (bottom notation), even less pronounced than in retinal ganglion cells.

Maps of visual fields in the lateral geniculate body

An important topographic feature is the high orderliness in the organization of receptive fields within each layer of the LKT. Neighboring regions of the retina form connections with neighboring cells of the LC, so that the receptive fields of nearby LC neurons overlap over a large area. Cells in the central zone of the cat's retina (the region where the cat's retina has small receptive fields with small centers) as well as in the fovea of the monkey form connections with a relatively large number of cells within each layer of the LCT. A similar distribution of bonds was found in humans using NMR. The number of cells associated with the peripheral regions of the retina is relatively small. This overrepresentation of the optic fossa reflects the high density of photoreceptors in the zone that is necessary for vision with maximum acuity. Although the number of optic nerve fibers and the number of LC cells are probably approximately equal, each LC neuron nevertheless receives convergent signals from several optic nerve fibers. Each fiber of the optic nerve in turn forms divergent synaptic connections with several LC neurons.

However, each layer is not only topographically ordered, but also the cells of different layers are in retinotopic relation to each other. That is, if the electrode is advanced strictly perpendicular to the surface of the LKT, then the activity of cells receiving information from the corresponding zones of one and then the other eye will be recorded first, as the microelectrode crosses one layer of the LKT after another. The location of the receptive fields is in strictly corresponding positions on both retinas, i.e. they represent the same area of the visual field. There is no significant mixing of information from the right and left eyes and interaction between them in the cells of the LKT, only a small number of neurons (which have receptive fields in both eyes) are excited exclusively binocularly.

Surprisingly, the responses of LCT cells do not differ dramatically from those of ganglion cells (Fig. 3). LCT neurons also have concentrically organized antagonistic receptive fields, either with an "off" or "on" center, but the contrast mechanism is finer tuned due to the greater correspondence between

inhibitory and excitatory zones. Thus, similarly to retinal ganglion cells, contrast is the optimal stimulus for LC neurons, but they respond even weaker to general illumination. The study of the receptive fields of LC neurons has not yet been completed. For example, neurons were found in the LCT, whose contribution to the work of the LCT has not been established, as well as pathways leading from the cortex down to the LCT. Cortical feedback is necessary for the synchronized activity of LC neurons.

Functional layers of LCT

Why does the LCT have more than one layer per eye? It has now been found that neurons in different layers have different functional properties. For example, cells found in the fourth dorsal small cell layer of the monkey LC, like P ganglion cells, are able to respond to light of different colors, showing good color discrimination. Conversely, layers 1 and 2 (large cell layers) contain M-like cells that give fast ("alive") responses and are color insensitive, while K layers receive signals from "blue-on" retinal ganglion cells and can play a special role in color vision. In cats, X and Y fibers (see section "Classification of ganglion cells" end in different sublayers A, C and A 1, therefore, specific inactivation of layer A, but not C, sharply reduces the accuracy of eye movements. Cells with "on" - and "off "-center is also divided into different layers in the LCT of mink and ferret, and, to some extent, in monkeys. In summary, the LCT is a staging station in which ganglion cell axons are sorted in such a way that neighboring cells receive signals from identical regions of the visual fields, and neurons that process information are organized in clusters.Thus, in the LCT, the anatomical basis for parallel processing of visual information is obvious.

Cytoarchitectonics of the visual cortex

Visual information enters the cortex and LCT through optical radiation. In monkeys, optical radiation ends at a folded plate about 2 mm thick (Fig. 4). This region of the brain - known as the primary visual cortex, visual area 1 or V 1 - is also called the striated cortex, or "area 17". Older terminology was based on anatomical criteria developed at the beginning of the 20th century. V 1 lies behind, in the region of the occipital lobe, and can be recognized in a transverse section by its special appearance. The bundles of fibers in this area form a strip that is clearly visible to the naked eye (which is why the zone is called “striped”, Fig. 4B). Neighboring zones outside the banding zone are also associated with vision. The area immediately surrounding zone V is called zone V 2 (or "zone 18") and receives signals from zone V, (see Figure 4C). The clear boundaries of the so-called extrastriate visual cortex (V 2 -V 5) cannot be established using visual examination of the brain, although a number of criteria have been developed for this. For example, in V 2 the striation disappears, large cells are located superficially, and coarse, oblique myelin fibers are visible in deeper layers.

Each zone has its own representation of the visual field of the retina, projected in a strictly defined, retinotopic way. Projection maps were compiled back in an era when it was not possible to analyze the activity of individual cells. Therefore, for mapping, illumination of small areas of the retina with light beams and registration of cortical activity using a large electrode were used. These maps, as well as their modern counterparts recently compiled using brain imaging techniques such as positron emission tomography and functional nuclear magnetic resonance, have shown that the area of the cortex devoted to representing the fovea is much larger than the area assigned to the rest of the retina. These findings, in principle, met expectations, since pattern recognition by the cortex is carried out mainly due to the processing of information from photoreceptors densely located in the fovea zone. This representation is analogous to the extended representation of the hand and face in the region of the primary somatosensory cortex. The retinal fossa projects into the occipital pole of the cerebral cortex. The retinal periphery map extends anteriorly along the medial surface of the occipital lobe (Fig. 5). Due to the inverted picture formed on the retina with the help of the lens, the upper visual field is projected onto the lower region of the retina and is transmitted to the region V 1 located below the spur groove; the lower visual field is projected over the spur groove.

On sections of the cortex, neurons can be classified according to their shape. The two main groups of neurons form stellate and pyramidal cells. Examples of these cells are shown in Fig. 6B. The main differences between them are the length of the axons and the shape of the cell bodies. Axons of pyramidal cells are longer, descend into the white matter, leaving the cortex; the processes of stellate cells end in the nearest zones. These two groups of cells may have other differences, such as the presence or absence of spines on the dendrites, which provide their functional properties. There are other bizarrely named neurons (two-flower cells, chandelier cells, basket cells, crescent cells), as well as neuroglial cells. Their characteristic feature is that the processes of these cells are directed mainly in the radial direction: up and down through the thickness of the cortex (at an appropriate angle to the surface). Conversely, many (but not all) of their lateral processes are short. Connections between the primary visual cortex and the higher order cortex are carried out by axons, which pass in the form of bundles through the white matter located under the cell layers.

Rice. 7. Connections of the visual cortex. (A) Layers of cells with different incoming and outgoing processes. Note that the original processes from the LKT are mostly interrupted in the 4th layer. The outgrowths from the LCT coming from the large cell layers are predominantly interrupted in the 4C and 4B layers, while the outgrowths from the small cell ones are interrupted in the 4A and 4C. Simple cells are located mainly in layers 4 and 6, complex cells - in layers 2, 3, 5 and 6. Cells in layers 2, 3 and 4B send axons to other cortical zones; cells in layers 5 and 6 send axons to the superior colliculus and LC. (B) Typical branching of axons of the LCT and cortical neurons in a cat. In addition to these vertical connections, many cells have long horizontal connections that run within one layer to distant regions of the cortex.

Incoming, outgoing pathways and layered organization of the cortex

The main feature of the mammalian cortex is that the cells here are arranged in 6 layers within the gray matter (Fig. 6A). The layers vary greatly in appearance, depending on the density of the cells, as well as the thickness of each of the zones of the cortex. Incoming paths are shown in fig. 7A on the left side. Based on the LCT, the fibers mainly terminate in layer 4 with a small number of connections formed also in layer 6. The superficial layers receive signals from the thalamic cushion area (pulvinarzone) or other areas of the thalamus. A large number of cortical cells, especially in the region of layer 2, as well as in the upper parts of layers 3 and 5, receive signals from neurons also located within the cortex. The bulk of the fibers coming from the LCT to layer 4 is then divided between the various sublayers.

Fibers outgoing from layers 6, 5, 4, 3 and 2 are shown on the right in Fig. 7A. Cells that send efferent signals from the cortex can also manage intracortical connections between different layers. For example, the axons of a cell from layer 6, in addition to the LCT, can also be directed to one of the other cortical layers, depending on the type of response of this cell 34) . Based on this structure of the visual pathways, the following pathway of the visual signal can be imagined: information from the retina is transmitted to the cortical cells (mainly in layer 4) by the axons of the LCT cells; information is transmitted from layer to layer, from neuron to neuron throughout the thickness of the cortex; processed information is sent to other areas of the cortex with the help of fibers that go deep into the white matter and return back to the area of the cortex. Thus, the radial or vertical organization of the cortex gives us reason to believe that the columns of neurons work as separate computing units, processing various details of visual scenes and forwarding the received information further to other regions of the cortex.

Separation of incoming fibers from LQT in layer 4

LCT afferent fibers terminate in layer 4 of the primary visual cortex, which has a complex organization and can be studied both physiologically and anatomically. The first feature we want to demonstrate is the separation of incoming fibers coming from different eyes. In adult cats and monkeys, cells within one layer of the LCT, receiving signals from one eye, send processes to strictly defined clusters of cortical cells in layer 4C, which are responsible for this particular eye. Accumulations of cells are grouped in the form of alternating strips or bundles of cortical cells that receive information exclusively from the right or left eye. In the more superficial and deeper layers, neurons are controlled by both eyes, although usually with a predominance of one of them. Hubel and Wiesel made an original demonstration of the separation of information from different eyes and the dominance of one of them in the primary visual cortex using electrophysiological methods. They used the term "ocular dominance columns" to describe their observations, following Mountcastle's concept of cortical columns for the somatosensory cortex. A series of experimental techniques were developed to demonstrate alternating groups of cells in layer 4 receiving information from the right or left eye. Initially, it was proposed to inflict a small amount of damage within only one layer of the LKT (recall that each layer receives information from only one eye). If this is done, then the degenerating terminals appear in layer 4, forming a certain pattern of alternating spots, which correspond to zones controlled by the eye, sending information to the damaged area of the LCT. Later, a startling demonstration of the existence of a particular ocular dominance pattern was made using the transport of radioactive amino acids from one eye. The experiment consists in injecting an amino acid (proline or lecithin) containing atoms of radioactive tritium into the eye. The injection is carried out in the vitreous body of the eye, from which the amino acid is captured by the bodies of retinal nerve cells and included in the protein. Over time, the protein labeled in this way is transported to the ganglion cells and along the optic nerve fibers to their terminals within the LCT. The remarkable feature is that this radioactive label is also transmitted from neuron to neuron through chemical synapses. The label eventually ends up at the end of the LCT fibers within the visual cortex.

On fig. 8 shows the location within layer 4 of the radioactive terminals formed by the axons of the LCT cells associated with the eye into which the label was injected.

Rice. Fig. 8. Eye-dominant columns in the monkey cortex obtained by injecting radioactive proline into one eye. Autoradiograms taken under dark-field illumination showing silver grains in white. (A) At the top of the figure, the slice passes through layer 4 of the visual cortex at an angle to the surface, forming a perpendicular slice of the columns. In the center, layer 4 has been cut horizontally, showing that the column consists of elongated plates. (B) Reconstruction from multiple horizontal sections of layer 4C in another monkey that was injected into the ilsilateral eye. (Any horizontal cut may reveal

only part of layer 4, due to the curvature of the cortex.) In both A and B, the visual dominance columns look like stripes of equal width, receiving information from either one or the other eye.

located directly above the visual cortex, so such areas look like white spots on the dark background of the photograph). Marker spots are interspersed with unmarked areas that receive information from the contralateral eye where the mark was not applied. The distance from center to center between the spots, which correspond to the eye-dominant columns, is approximately 1 mm.

At the cellular level, a similar structure was revealed in layer 4 by injecting horseradish peroxidase into individual cortical-bound axons of LC neurons. The axon shown in Fig. 9 comes from the LCT neuron with an "off" center that responds with short signals to shadows and moving spots. The axon terminates in two different groups of processes in layer 4. The groups of labeled processes are separated by an empty unlabeled zone corresponding in size to the territory responsible for the other eye. This kind of morphological study expands the boundaries and allows a deeper understanding of the original description of the columns of ocular dominance, compiled by Hubel and Wiesel in 1962.

Literature

1. o Hubel, D. H. 1988. Eye, Brain and Vision. Scientific American Library. new york.

2.o Ferster, D., Chung, S., and Wheat, H. 1996. Orientation selectivity of thalamic input to simple cells of cat visual cortex. Nature 380: 249-252.

3. o Hubel, D. H., and Wiesel, T. N. 1959. Receptive fields of single neurones in the cat's striate cortex. /. Physiol. 148: 574-591.

4. About Hubel, D.H., and Wiesel, T.N. 1961. Integrative action in the cat's lateral geniculate body. /. Physiol. 155: 385-398.

5. O Hubel, D. H., and Wiesel, T. N. 1962. Receptive fields, binocular interaction and functional architecture in the cat's visual cortex. /. Physiol. 160: 106-154.

Optic nerve fibers start from each eye and end on the cells of the right and left lateral geniculate body (LCT) (Fig. 1), which has a clearly distinguishable layered structure (“geniculate” - geniculate - means “curved like a knee”). In the LCT of a cat, three distinct, well-defined cell layers (A, A 1 , C) can be seen, one of which (A 1) has a complex structure and is further subdivided. In monkeys and other primates, including

Rice. 1. Lateral geniculate body (LCB). (A) Cat LCT has three cell layers: A, A, and C. (B) Monkey LCT has 6 major layers, including small cell (parvocellular), or C (3, 4, 5, 6), large cell (magnocellular ), or M (1, 2) separated by koniocellular layers (K). In both animals, each layer receives signals from only one eye and contains cells that have specialized physiological properties.

In both the cat and the monkey, each layer of the LCT receives signals from either one eye or the other. In monkeys, layers 6, 4, and 1 receive information from the contralateral eye, and layers 5, 3, and 2 from the ipsilateral eye. The separation of the course of nerve endings from each eye into different layers has been shown using electrophysiological and a number of anatomical methods. Particularly surprising is the type of branching of an individual fiber of the optic nerve when horseradish peroxidase is injected into it (Fig. 2).

This is the subcortical center, which ensures the transmission of information already in the visual cortex.

In humans, this structure has six layers of cells, as in the visual cortex. Fibers from the retina come crossed and uncrossed to the chiasma opticus. 1st, 4th, 6th layers receive crossed fibers. 2nd, 3rd, 5th layers are received uncrossed.

All information coming to the lateral geniculate body from the retina is ordered and the retinotopic projection is preserved. Since the fibers enter the lateral geniculate body in a comb-like manner, there are no neurons in the NKT that receive information from two retinas simultaneously. It follows from this that there is no binocular interaction in NKT neurons. Fibers from M-cells and P-cells enter the tubing. The M-path, which communicates information from large cells, transmits information about the movements of objects and ends in the 1st and 2nd layers. The P-path is associated with color information and the fibers terminate in the 3rd, 4th, 5th, 6th layers. In the 1st and 2nd layers of the tubing, the receptive fields are highly sensitive to motion and do not distinguish spectral characteristics (color). Such receptive fields are also present in small amounts in other layers of the tubing. In the 3rd and 4th layers, neurons with an OFF center predominate. It is blue-yellow or blue-red + green. In the 5th and 6th layers, neurons with ON centers are mainly red-green. The receptive fields of the cells of the lateral geniculate body have the same receptive fields as the ganglion cells.

The difference between these receptive fields and ganglion cells:

1. In the sizes of receptive fields. The cells of the lateral geniculate body are smaller.

2. Some neurons of the NKT have an additional inhibitory zone surrounding the periphery.

For cells with an ON center, such an additional zone will have a reaction sign coinciding with the center. These zones are formed only in some neurons due to increased lateral inhibition between the neurons of the NKT. These layers are the basis for the survival of a particular species. Humans have six layers, predators have four.

Detector theory appeared in the late 1950s. In the frog retina (in ganglion cells), reactions were found that were directly related to behavioral responses. Excitation of certain retinal ganglion cells led to behavioral responses. This fact made it possible to create the concept, according to which the image presented on the retina is processed by ganglion cells specifically tuned to image elements. Such ganglion cells have a specific dendritic branching that corresponds to a certain structure of the receptive field. Several types of such ganglion cells have been found. Subsequently, neurons with this property were called detector neurons. Thus, a detector is a neuron that reacts to a certain image or part of it. It turned out that other, more highly developed animals also have the ability to highlight a specific symbol.

1. Convex edge detectors - the cell was activated when a large object appeared in the field of view;

2. A moving small contrast detector - its excitation led to an attempt to capture this object; in contrast corresponds to the captured objects; these reactions are associated with food reactions;

3. Blackout detector - causes a defensive reaction (the appearance of large enemies).

These retinal ganglion cells are tuned to highlight certain elements of the environment.

A group of researchers working on this topic: Letvin, Maturano, Mokkalo, Pitz.

Neurons of other sensory systems also have detector properties. Most detectors in the visual system are associated with motion detection. Neurons have increased reactions with an increase in the speed of movement of objects. Detectors have been found in both birds and mammals. The detectors of other animals are directly connected to the surrounding space. The birds were found to have horizontal surface detectors, which is associated with the need to land on horizontal objects. Detectors of vertical surfaces have also been found, which provide the birds' own movements towards these objects. It turned out that the higher the animal in the evolutionary hierarchy, the higher the detectors are, i.e. these neurons can already be located not only in the retina, but also in the higher parts of the visual system. In higher mammals: in monkeys and humans, the detectors are located in the visual cortex. This is important because the specific way that provides responses to elements of the external environment is transferred to the higher levels of the brain, and at the same time, each animal species has its own specific types of detectors. Later it turned out that in ontogenesis the detector properties of sensory systems are formed under the influence of the environment. To demonstrate this property, experiments were done by researchers, Nobel laureates, Hubel and Wiesel. Experiments were carried out that proved that the formation of detector properties occurs in the earliest ontogeny. For example, three groups of kittens were used: one control and two experimental. The first experimental one was placed in conditions where mainly horizontally oriented lines were present. The second experimental was placed in conditions where there were mostly horizontal lines. The researchers tested which neurons formed in the cortex of each group of kittens. In the cortex of these animals, there were 50% of neurons that were activated both horizontally and 50% vertically. Animals brought up in a horizontal environment had a significant number of neurons in the cortex that were activated by horizontal objects, there were practically no neurons that were activated when perceiving vertical objects. In the second experimental group there was a similar situation with horizontal objects. The kittens of both horizontal groups had certain defects. Kittens in a horizontal environment could perfectly jump on steps and horizontal surfaces, but did not perform well relative to vertical objects (table leg). The kittens of the second experimental group had a corresponding situation for vertical objects. This experiment proved:

1) formation of neurons in early ontogenesis;

2) the animal cannot adequately interact.

Changing animal behavior in a changing environment. Each generation has its own set of external stimuli that produce a new set of neurons.

Specific features of the visual cortex

From the cells of the external geniculate body (has a 6-layer structure), axons go to 4 layers of the visual cortex. The bulk of the axons of the lateral geniculate body (NKT) is distributed in the fourth layer and its sublayers. From the fourth layer, information flows to other layers of the cortex. The visual cortex retains the principle of retinotopic projection in the same way as the LNT. All information from the retina goes to the neurons of the visual cortex. The neurons of the visual cortex, like the neurons of the underlying levels, have receptive fields. The structure of the receptive fields of neurons in the visual cortex differs from the receptive fields of the NKT and retinal cells. Hubel and Wiesel also studied the visual cortex. Their work made it possible to create a classification of the receptive fields of neurons in the visual cortex (RPNZrK). H. and V. found that RPNZrK are not concentric, but rectangular in shape. They can be oriented at different angles, have 2 or 3 antagonistic zones.

Such a receptive field can highlight:

1. change in illumination, contrast - such fields were called simple receptive fields;

2. neurons with complex receptive fields- can allocate the same objects as simple neurons, but these objects can be located anywhere in the retina;

3. supercomplex fields- can select objects that have gaps, borders or changes in the shape of the object, i.e. highly complex receptive fields can highlight geometric shapes.

Gestalts are neurons that highlight subimages.

The cells of the visual cortex can only form certain elements of the image. Where does constancy come from, where does the visual image appear? The answer was found in association neurons, which are also associated with vision.

The visual system can distinguish various color characteristics. The combination of opponent colors allows you to highlight different shades. Lateral inhibition is required.

Receptive fields have antagonistic zones. The neurons of the visual cortex are able to fire peripherally to green, while the middle is fired to the action of a red source. The action of green will cause an inhibitory reaction, the action of red will cause an excitatory reaction.

The visual system perceives not only pure spectral colors, but also any combination of shades. Many areas of the cerebral cortex have not only a horizontal, but also a vertical structure. This was discovered in the mid 1970s. This has been shown for the somatosensory system. Vertical or columnar organization. It turned out that in addition to the layers, the visual cortex also has vertically oriented columns. Improvement in registration techniques led to more subtle experiments. The neurons of the visual cortex, in addition to the layers, also have a horizontal organization. A microelectrode was passed strictly perpendicular to the surface of the cortex. All major visual fields are in the medial occipital cortex. Since the receptive fields have a rectangular organization, dots, spots, any concentric object does not cause any reaction in the cortex.

Column - type of reaction, the adjacent column also highlights the slope of the line, but it differs from the previous one by 7-10 degrees. Further studies have shown that columns are located nearby, in which the angle changes with an equal step. About 20-22 adjacent columns will highlight all slopes from 0 to 180 degrees. The set of columns capable of highlighting all the gradations of this feature is called a macrocolumn. These were the first studies that showed that the visual cortex can highlight not only a single property, but also a complex - all possible changes in a trait. In further studies, it was shown that next to the macrocolumns that fix the angle, there are macrocolumns that can highlight other image properties: colors, direction of movement, speed of movement, as well as macrocolumns associated with the right or left retina (columns of eye dominance). Thus, all macrocolumns are compactly located on the surface of the cortex. It was proposed to call sets of macrocolumns hypercolumns. Hypercolumns can analyze a feature set of images located in a local area of the retina. Hypercolumns is a module that highlights a set of features in a local area of the retina (1 and 2 are identical concepts).

Thus, the visual cortex consists of a set of modules that analyze the properties of images and create subimages. The visual cortex is not the final stage in the processing of visual information.

Properties of binocular vision (stereo vision)

These properties make it easier for both animals and humans to perceive the remoteness of objects and the depth of space. In order for this ability to manifest itself, eye movements (convergent-divergent) to the central fovea of the retina are required. When considering a distant object, there is a separation (divergence) of the optical axes and convergence for closely spaced ones (convergence). Such a system of binocular vision is presented in different animal species. This system is most perfect in those animals in which the eyes are located on the frontal surface of the head: in many predatory animals, birds, primates, most predatory monkeys.

In another part of the animals, the eyes are located laterally (ungulates, mammals, etc.). It is very important for them to have a large volume of perception of space.

This is due to the habitat and their place in the food chain (predator - prey).

With this method of perception, the perception thresholds are reduced by 10-15%, i.e. organisms with this property have an advantage in the accuracy of their own movements and their correlation with the movements of the target.

There are also monocular signs of the depth of space.

Properties of binocular perception:

1. Fusion - the fusion of completely identical images of two retinas. In this case, the object is perceived as two-dimensional, planar.

2. Fusion of two non-identical retinal images. In this case, the object is perceived three-dimensionally.

3. Rivalry of visual fields. Two different images come from the right and left retinas. The brain cannot combine two different images, and therefore they are perceived alternately.

The rest of the retinal points are disparate. The degree of disparity will determine whether the object is perceived three-dimensionally or whether it will be perceived with rivalry of fields of view. If the disparity is low, then the image is perceived three-dimensionally. If the disparity is very high, then the object is not perceived.

Such neurons were found not in the 17th, but in the 18th and 19th fields.

What is the difference between the receptive fields of such cells: for such neurons in the visual cortex, the receptive fields are either simple or complex. In these neurons, there is a difference in receptive fields from the right and left retinas. The disparity of the receptive fields of such neurons can be either vertical or horizontal (see next page):

This property allows for better adaptation.

(+) The visual cortex does not allow us to say that a visual image is formed in it, then constancy is absent in all areas of the visual cortex.

Similar information.