Signal coding in the lateral geniculate body and primary visual cortex

The retinal ganglion cells project their processes into the lateral geniculate body, where they form the 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 that form layers of large-cell (magnocellular), small-cell (parvocellular) and koniocellular (koniocellular) neurons. The neurons of the lateral geniculate body have receptive fields of the "center-background" type, similar to the ganglion cells of the retina.

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

Two classes of neurons in the V 1 region have been described, which 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 region 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 adjacent centers of several receptive fields form one cortical receptive zone. The complex cell field is dependent on signals from the simple cell and other cortical cells. The sequential 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 on the next, where an even more abstract concept is formed on the basis of the initial information. At all levels of the visual analyzer, special attention is paid to contrast and definition of the boundaries of the image, rather than the overall illumination of the eye. Thus, complex cells of the visual cortex can "see" the lines that are the boundaries of the rectangle, and they do not care much about the absolute intensity of light within this rectangle. A series of clear and continuing each other research in the field of mechanisms of perception of visual information, begun by Kuffler's pioneering work with the retina, was continued at the level of the visual cortex by Huebel and Wiesel. Hubel gave a vivid description of early experiments on the visual cortex in the laboratory of Stephen Kuffler at Johns Hopkins University (USA) in the 50s of the XX century. Since then, our understanding of the physiology and anatomy of the cerebral hemispheres has developed significantly through the experiments of Huebel and Wiesel, as well as through the large number of works for which their research was the starting point or source of inspiration. Our goal is to provide a concise, narrative description of signal coding and cortical architecture in terms of perception, based on the classics of Huebel and Wiesel, as well as later experiments performed 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 visual cortex, as well as their role in providing the first steps in the analysis of visual sienna: defining lines and shapes based on the signal from the retina in the form of "center-background".

When moving from the retina to the lateral geniculate body, and then to the cerebral cortex, questions arise that are beyond the limits of technology. For a long time it has been generally accepted that in order to understand the functioning of any part nervous system knowledge about the properties of its constituent neurons is necessary: ​​how they conduct signals and carry information, how they transmit the information received 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 this: 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?

On closer examination, the logic of such arguments regarding the underlying 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 clear 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 structure of neural tissue is closely intertwined with the retinotopic map of the visual cortex. Thus, adjacent points of the retina are projected onto adjacent 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, with the help of methods that make it possible to isolate functionally related cell ensembles, patterns of cortical organization of a higher level were identified. Indeed, the architecture of the cortex defines the structural basis of cortical function, and therefore new anatomical approaches inspire new analytical research. Thus, before we describe the functional connections of visual neurons, it is useful to briefly summarize the general structure of the central visual pathways, starting from the nuclei of the lateral geniculate body.

Lateral geniculate body

Optic nerve fibers begin in 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” - means “bent like a knee”). In the cat's LCT, you can see three distinct, well-distinguishable layers of cells (A, A1, C), one of which (A1) has a complex structure and is further subdivided. In monkeys and other primates including

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

In both the cat and the monkey, each layer of LCT receives signals from either one or the other eye. 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 variety of anatomical methods. Particularly surprising is the type of branching of an individual optic nerve fiber when the enzyme horseradish peroxidase is injected into it (Fig. 2).

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

Rice. 2. The endings of the optic nerve fibers in the cat's LCT. Horseradish peroxidase was injected into one of the axons from the "on" zone in the center of the contralateral eye. Axon branches end on cells in layers A and C, but not A1.

Rice. 3. Receptive fields of cells of PC. The concentric receptive fields of the LBT cells resemble those of the ganglion cells in the retina, dividing into fields with an "on" and an "off" center. The responses of a cell with an "on" center of the Feline LBT are shown. The bar above the signal indicates the duration of illumination. zones neutralize the effects of each other, therefore, diffuse illumination of the entire receptive field gives only weak responses (lower record), even less pronounced than in the ganglion cells of the retina.

Visual field maps in the lateral geniculate body

An important topographic feature is a high orderliness in the organization of receptive fields within each layer of the LCT. Adjacent regions of the retina form connections with neighboring cells of the LCT, so that the receptive fields of nearby LCT neurons overlap over a large area. Cells in the central area of ​​the feline retina (the region where the feline retina has small receptive fields with small centers), as well as the monkey's optic fossa, 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. Such an overrepresentation of the optic fossa reflects a high density of photoreceptors in the zone that is necessary for vision with maximum acuity. Although, probably, the number of optic nerve fibers and the number of LBT cells are approximately equal, nevertheless, each LBT neuron receives converging signals from several fibers of the optic nerve. Each fiber of the optic nerve, in turn, forms divergent synaptic connections with several neurons of the LCT.

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

Surprisingly, the responses of the LCT cells do not differ strikingly from the signals of the ganglion cells (Fig. 3). LBT neurons also have concentrically organized antagonizing receptive fields, either with an "off" or an "on" center, but the contrast mechanism is adjusted more subtly, due to greater correspondence between

inhibitory and exciting zones. Thus, like retinal ganglion cells, contrast is the optimal stimulus for LBT neurons, but they react even weaker to general illumination. The study of the receptive fields of the LCT neurons has not yet been completed. For example, in the LCT, neurons were found whose contribution to the work of the LCT was not established, as well as paths going from the cortex down to the LCT. Cortical feedback is required for the synchronized activity of LCT neurons.

LCT functional layers

Why does LKT have more than one layer per eye? It has now been found that neurons in different layers have different functional properties. For example, cells located in the fourth dorsal small cell layers of the monkey LCT, like Ρ 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, which give rapid ("live") responses and are insensitive to color, while the K layers receive signals from the "blue-on" retinal ganglion cells and can play a special role in color vision. In cats, X and Y fibers (see the section "Classification of ganglion cells" end in different sublayers A, C and A1, therefore specific inactivation of layer A, but not C, sharply reduces the accuracy of eye movements. Cells with "on" - and "off "-centers are also subdivided into different layers in mink and ferret LBTs and, to some extent, in monkeys. In summary, LBT is a transfer 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 processing information are organized in the form of clusters.Thus, in LCT, the anatomical basis for parallel processing of visual information is obvious.

Cytoarchitectonics of the visual cortex

Visual information enters the cortex and LBT through optical radiation. In monkeys, optical radiation ends on a folded plate, about 2 mm thick (Fig. 4). This region of the brain - known as the primary visual cortex, visual zone 1 or V 1 - is also called striated cortex, or "zone 17". The older terminology was based on anatomical criteria developed back in the early 20th century. V 1 lies behind, in the region of the occipital lobe, and can be recognized in cross-section by its special appearance. The bundles of fibers in this area form a strip that is clearly visible to the naked eye (this is why the area is called “striped”, Fig. 4B). Neighboring zones outside the banding zone are also associated with vision. The area immediately surrounding area V is called area V 2 (or “area 18”) and receives signals from area V (see Figure 4C). Clear boundaries of the so-called extrastriatal 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 striped striation disappears, large cells are located superficially, and coarse, oblique myelin fibers are visible in deeper layers.

Each zone has its own view of the retinal visual field, projected in a strictly defined, retinotopic way. Projection maps were compiled back in the era when it was not possible to analyze the activity of individual cells. Therefore, for mapping, the illumination of small areas of the retina with light beams and registration of the activity of the cortex using a large electrode was used. These cards as well as their modern analogues recently compiled using imaging techniques such as positron emission tomography and functional nuclear magnetic resonance imaging, have shown that the area of ​​the cortex devoted to representing the central fossa is much larger than the area devoted to the rest of the retina. These findings, in principle, corresponded to expectations, since the recognition of images by the cortex is carried out mainly due to the processing of information from photoreceptors densely located in the fossa zone. This view is similar to an expanded view of the hand and face in 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 transmitted to the region V 1 located below the groove; the lower visual field is projected over the spur furrow.

In cortical slices, 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 the two are the length of the axons and the shape of the cell bodies. The axons of the pyramidal cells are longer, descending 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, fancifully named neurons (double-bouquette cells, chandelier cells, basket cells, crescent cells), as well as neuroglia 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 a corresponding 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 made by axons that run in bundles through the white matter under the cell layers

Rice. 7. Connections of the visual cortex. (A) Layers of cells with various incoming and outgoing processes. Note that the initial processes from the LCT are mainly interrupted in the 4th layer. The processes from the LCT, coming from the large-cell layers, are predominantly interrupted in the 4C and 4B layers, while the processes from the small-cell layers 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 areas; cells in layers 5 and 6 send axons to the upper hillock and LCT. (B) Typical branching of feline LCT axons and cortical neurons. In addition to such vertical connections, many cells have long horizontal connections that extend within one layer to distant regions of the cortex.

Inbound, outbound pathways and layered cortex organization

The main feature of the mammalian cortex is that the cells are located here in the form of 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 LCT, the fibers generally end in layer 4 with few bonds also formed in layer 6. Surface layers receive signals from the pulvinar zone or other thalamic zones. 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 are then divided between the various sublayers.

Fibers emanating from layers 6, 5, 4, 3, and 2 are shown on the right in Figure 7A. Cells that send efferent signals from the cortex can also drive 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 path of the visual signal can be imagined: information from the retina is transmitted to the cells of the cortex (mainly to layer 4) by the axons of the cells of the LCT; information is transmitted from layer to layer, from neuron to neuron throughout the entire thickness of the cortex; the processed information is sent to other areas of the cortex using fibers that travel 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 computational units, processing various details of visual scenes and sending the information received further to other regions of the cortex.

Separation of incoming fibers from LCT in layer 4

The afferent fibers of the LCT end 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 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 is responsible for this particular eye. Clusters of cells are grouped as alternating bands or bundles of cortical cells that receive information exclusively from the right or left eye. In more superficial and deeper layers, neurons are controlled by both eyes, although usually with a predominance of one of them. Huebel and Wiesel performed an original demonstration of the separation of information from different eyes and the predominance of one of them in the primary visual cortex using electrophysiological methods. They used the term "ocular dominance columns" to describe their observations, adhering to Mountcastle's concept of cortical columns for the somatosensory cortex. A series of experimental techniques have been developed to demonstrate alternating groups of cells in layer 4 receiving information from the right or left eye. Initially, it was proposed to inflict minor damage within only one layer of LCT (recall that each layer receives information from only one eye). If this is done, then degenerating terminals appear in layer 4, forming a certain pattern of alternating spots that correspond to the zones controlled by the eye, sending information to the damaged area of ​​the LCT. Later, a striking demonstration of the existence of a specific pattern of ocular dominance was performed using the transport of radioactive amino acids from one eye. The experiment consists in injecting an amino acid (proline or lecithin) containing radioactive tritium atoms into the eye. The injection is carried out into the vitreous body of the eye, from which the amino acid is captured by the bodies of the retinal nerve cells and incorporated into the protein. Over time, the protein labeled in this way is transported to the ganglion cells and along the fibers of the optic nerve to their terminals within the LCT. A remarkable feature is that this radioactive label is also transmitted from neuron to neuron via chemical synapses. Ultimately, the mark enters the end of the LCT fibers within the visual cortex.

In 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. 8. Ocular dominant columns in the cortex of a monkey obtained by injecting radioactive proline into one eye. Autoradiograms taken under dark field illumination, where silver grains are shown in white. (A) From 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 was cut horizontally, showing that the column is composed of elongated plates. (B) Reconstruction from multiple horizontal slices of layer 4C in another monkey injected into the ilsilateral eye. (Any horizontal cut can reveal

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

are located directly above the visual cortex, so such areas appear as white spots against a dark background of the photograph). The spots from the marks are interspersed with areas without marks, which receive information from the contralateral eye, where the mark was not inserted. The center-to-center distance between the spots that correspond to the oculominal columns is approximately 1 mm.

At the cellular level, a similar structure was revealed in layer 4 by injecting horseradish peroxidase into separate axons of LBT neurons heading to the cortex. The axon shown in Fig. 9, comes from the LKT neuron with an "off" center, which responds with short signals to shadows and moving spots. The axon ends 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 research expands the boundaries and allows a deeper understanding of the original description of the columns of ocular dominance, compiled by Huebel and Wiesel in 1962.

Literature

2. About 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. About 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. About 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.

Similar works to - Signal coding in the lateral geniculate body and primary visual cortex

External geniculate body

The axons of the optic tract approach one of the four second-order perceiving and integrating centers. The nuclei of the lateral geniculate body and the superior tubercles of the quadruple are the most important target structures for visual function. The geniculate bodies form a "knee-like" bend, and one of them - lateral (that is, lying farther from the median plane of the brain) - is associated with vision. The hillocks of the quadruple are two paired elevations on the surface of the thalamus, of which the upper ones deal with vision. The third structure - the suprachiasmatic nuclei of the hypothalamus (located above the optic chiasm) - use information about the intensity of light to coordinate our internal rhythms. Finally, the oculomotor nuclei coordinate eye movements when we look at moving objects.

Lateral geniculate nucleus. The axons of the ganglion cells form synapses with the cells of the lateral geniculate body in such a way that the display of the corresponding half of the visual field is restored there. These cells, in turn, send axons to cells in the primary visual cortex, a zone in the occipital lobe of the cortex.

The upper tubercles of the quadruple. Many ganglion cell axons branch out before reaching the lateral geniculate nucleus. While one branch connects the retina with this nucleus, the other goes to one of the secondary-level neurons in the superior tubercle of the quadruple. As a result of this branching, two parallel pathways are created from the ganglion cells of the retina to two different centers of the thalamus. In this case, both branches retain their retinotopic specificity, that is, they come to the points that together form an ordered projection of the retina. The neurons of the superior tubercle, which receive signals from the retina, send their axons to a large nucleus in the thalamus called the cushion. This nucleus grows ever larger in the series of mammals as their brain becomes more complex and reaches its greatest development in humans. The large size of this formation makes it possible to think that it performs some special functions in humans, but its true role is still unclear. Along with the primary visual signals, the neurons of the superior tubercles receive information about sounds emanating from certain sources and about the position of the head, as well as processed visual information returning through a feedback loop from neurons of the primary visual cortex. On this basis, it is believed that the hillocks serve as the primary centers of integration of information used by us for spatial orientation in a changing world.

Visual cortex

The bark has a layered structure. The layers differ from each other in the structure and shape of the neurons that form them, as well as in the nature of the connection between them. By their shape, the neurons of the visual cortex are divided into large and small, stellate, bush-shaped, fusiform.

The famous neuropsychologist Lorente de No in the 40s. the twentieth century discovered that the visual cortex is divided into vertical elementary units, which are a chain of neurons located in all layers of the cortex.

Synaptic connections in the visual cortex are very diverse. In addition to the usual division into axosomatic and axodendric, terminal and collateral, they can be divided into two types: 1) synapses with a long length and multiple synaptic endings and 2) synapses with a short length and single contacts.

The functional significance of the visual cortex is extremely high. This is proved by the presence of numerous connections not only with specific and nonspecific nuclei of the thalamus, reticular formation, dark associative area, etc.

On the basis of electrophysiological and neuropsychological data, it can be argued that at the level of the visual cortex, a subtle, differentiated analysis of the most complex signs of the visual signal is carried out (highlighting the contours, outlines, shape of the object, etc.). At the level of the secondary and tertiary areas, apparently, the most complex integrative process takes place, preparing the body for the recognition of visual images and the formation of a sensory-perceptual picture of the world.

brain retina occipital visual

Table of contents of the subject "Receptor potential of rods and cones. Receptive fields of retinal cells. Pathways and centers of the visual system. Visual perception.":
1. Receptor potential of rods and cones. Ion current through the photoreceptor membrane in the dark and in the light.
2. Adaptation of photoreceptors to changes in illumination. Light adaptation. Desensitization. Dark adaptation.
3. Receptive fields of retinal cells. Direct pathway of signal transmission from photoreceptors to the ganglion cell. Indirect signaling path.
4. Receptive fields with on-centers and off-centers. On-neurons. Off-neurons. On-type ganglion cell. Off-type ganglion cell.
5. Receptive fields of color perception. Perception of color. Primary colors. Monochromasia. Dichromasia. Trichromasia.
6. M- and P-types of retinal ganglion cells. Magnocellular (M-cells) cells. Parvocellular (P-cells) retinal ganglion cells.
7. Pathways and centers of the visual system. The optic nerve. Visual tracts. Oculomotor reflex.
8. Lateral geniculate body. Functional organization of the lateral geniculate body. Receptive fields of the lateral geniculate body.
9. Processing of visual sensory information in the cortex. Projection visual cortex. Light edge. Complex neurons. Double anti-color cells.
10. Visual perception. Magnocellular pathway. Parvocellular pathway. Perception of form, color.

Lateral geniculate body. Functional organization of the lateral geniculate body. Receptive fields of the lateral geniculate body.

Ganglion cell axons form topographically organized connections with neurons of the lateral geniculate body, which are represented by six layers of cells. The first two layers, located ventrally, consist of magnocellular cells that have synapses with the M-cells of the retina, the first layer receiving signals from the nasal half of the retina of the contralateral eye, and the second from the temporal half of the ipsilateral eye. The remaining four layers of cells located dorsally receive signals from P-cells of the retina: the fourth and sixth from the nasal half of the retina of the contralateral eye, and the third and fifth from the temporal half of the retina of the ipsilateral eye. As a result of this organization of afferent inputs in each lateral geniculate body, that is, left and right, are formed six located exactly one above the other neural maps of the opposite half of the visual field. Neural maps are organized retinotopically, in each of them about 25% of cells receive information from the photoreceptors of the central fossa.

Receptive fields of neurons of the lateral geniculate body have a rounded shape with on- or off-type centers and a periphery antagonistic to the center. A small number of ganglion cell axons converge to each neuron, and therefore the nature of the information transmitted to the visual cortex remains almost unchanged. Signals from the retinal parvocellular and magnocellular cells are processed independently of each other and transmitted to the visual cortex in parallel paths. Neurons lateral geniculate body receive from the retina no more than 20% of afferent inputs, and the remaining afferents are formed mainly by neurons of the reticular formation and cortex. These entrances to lateral geniculate body regulate the transmission of signals from the retina to the cortex.

represents a small elongated eminence at the postero-lower end of the optic hillock, lateral to the pulvinar. In the ganglion cells of the lateral 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 terminate in the lateral geniculate body, still a small part of them goes to the pulvinar and the anterior quadruple. These anatomical data served as the basis for the opinion widespread for a long time, according to which both the external geniculate body and the pulvinar and the anterior quadruple were considered primary visual centers.

At the present time, a lot of data has accumulated that do not allow us to consider the pulvinar and the anterior quadruple to be primary visual centers.

Comparison of clinical and pathological data, as well as data of embryology and comparative anatomy, does not allow us to ascribe the role of the primary visual center to pulvinar. So, according to Genshen's observations, in the presence of pathological changes in the pulvinar, the field of vision remains normal. Browver notes that with a modified lateral geniculate body and an unchanged pulvinar, homonymous hemianopsia is observed; with changes in the pulvinar and unchanged external geniculate body, the field of vision remains normal.

The situation is similar with anterior quadruple... The fibers of the optic tract form the visual layer in it and end in the 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.

Moving on to the question of the projection of the retina in the lateral geniculate body, the following should be noted. Monakov in general denied having any retinal projection in the lateral geniculate body... He believed that all fibers coming from different parts of the retina, including papillomacular, are evenly distributed throughout the 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, he found limited changes in the dorsal part of the lateral geniculate body during postmortem examination.

Ronne with atrophy of the optic nerves with central scotomas on the soil alcohol intoxication found limited changes in ganglion cells in the lateral geniculate body, indicating that the macular region is projected onto the dorsal geniculate body.

The above observations prove beyond doubt the presence of a certain projection of the retina in the lateral geniculate body... But the clinical and anatomical observations available in this respect are too few in number and do not yet give an accurate idea of ​​the nature of this projection. The experimental studies of Brower and Zeman on monkeys, which we mentioned, made it possible to some extent to study 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 half moon, 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 are projected ventromedially onto the lateral geniculate body; the lower quadrants are ventro-lateral. The projection of the retina in the lateral geniculate body in a monkey is shown in Fig. eight.

In the external 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 research of M. Minkowski makes a significant contribution to the clarification of this issue. He found that in a number of animals after enucleation of one eye, as well as in humans with prolonged one-sided blindness 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 spreads with a certain regularity to various layers of ganglion cells. In the outer geniculate body on each side, layers of atrophied ganglion cells alternate with layers in which the cells remain normal. The 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. Based on his observations, Minkowski came to the conclusion that each eye has a separate representation in the lateral geniculate body... Crossed and uncrossed fibers thus terminate at different layers of ganglion cells, as is well depicted in Le Gros Clark's diagram (Fig. 10).

Rice. ten. Scheme of the end of the fibers of the optic tract and the beginning of the fibers of the Graziole bundle in the lateral geniculate body (according to Le Gros Clark).
Solid lines - crossed fibers, broken lines - uncrossed fibers. 1 - the optic tract; 2 - external geniculate body; 3 - Graziole's beam; 4 - the cortex of the occipital lobe.

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

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

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

External geniculate body (corpus genicu-latum laterale) is the location of the so-called "second neuron" of the visual pathway. About 70% of the fibers of the optic tract pass through the lateral geniculate body. The external geniculate body is an elevation corresponding to the location of one of the nuclei of the optic tubercle (Fig. 4.2.26-4.2.28). It contains about 1 800 000 neurons, on the dendrites of which the axons of the retinal ganglion cells end.

Previously, it was assumed that the lateral geniculate body is only a "relay station" that transmits information from retinal neurons through the visual radiance of the cerebral cortex. It has now been shown that at the level of the lateral geniculate body there is a rather significant and diverse processing of visual information. The neurophysiological significance of this formation will be discussed below. Initially required

Rice. 4.2.26. Left lateral geniculate body model (by Wolff, 1951):

a- rear and inside view; b - rear and outside view (/ - visual tract; 2 - saddle; 3 - visual radiance; 4 - head; 5 - body; 6 - isthmus)

dimo to dwell on its anatomical features.

The nucleus of the lateral geniculate body is one of the nuclei of the optic hillock. It is located between the ventroposteriolateral nucleus of the optic tubercle and the cushion of the optic tubercle (Fig. 4.2.27).

The outer geniculate nucleus consists of the dorsal and phylogenetically more ancient ventral nuclei. The ventral nucleus in humans is preserved as a rudiment and consists of a group of neurons located rostral to the dorsal nucleus. In lower mammals, this nucleus provides the most primitive photostatic reactions. The fibers of the optic tract do not fit into this nucleus.

The dorsal nucleus constitutes the main part of the nucleus of the lateral geniculate body. It is a multilayer structure in the form of a saddle or an asymmetric cone with a rounded top (Fig. 4.2.25-4.2.28). The horizontal section shows that the external geniculate body is connected in front with the optic tract, from the lateral side - with the retrolenticular part of the inner capsule, medially with the middle geniculate body, posteriorly with the hippocampal gyrus, and posteriolaterally - with the lower horn of the lateral ventricle. The cushion of the optic tubercle is adjacent to the nucleus of the lateral geniculate body from above, anterio-laterally - temporopontin fibers and the posterior part of the inner capsule, laterally - Wernicke's zone, and on the inner side - the medial nucleus (Fig. 4.2.27). Wernicke's zone is the innermost part of the inner capsule. It is in it that visual radiance begins. The fibers of visual radiance are located on the dorsolateral side of the nucleus of the lateral geniculate body, while the fibers of the auditory tract are located on the dorsomedial side.

■ .■. ■>

Rice. 4.2.27. The lateral geniculate body and its relation to the structures of the brain:

a- horizontal section of the brain (/ - external geniculate body; 2 - internal capsule; 3 - pillow of the optic hillock); b - sagittal section of the brain (histological section stained with hematoxylin and eosin) (Tubing- external geniculate body)

The lateral geniculate is connected to the superior quadruple by a ligament called the anterior shoulder.

Even with a macroscopic examination of the lateral geniculate body, it is revealed that this formation has a layered structure. Monkeys and humans clearly distinguish six bands of "gray matter" and located between them "white" layers, consisting of axons and dendrites (Fig. 4.2.28). The first layer is the layer located on the ventral side. The two inner layers are composed of large cells (magnocellular layers 1 and 2). They got this name

Rice. 4.2.28. External geniculate body:

/ - hippocampus; 2 - subarochnoid space; 3 - the leg of the brain; 4 - layer 1; 5 - layer 2; 6 - the lower horn of the lateral ventricle; 7 - layer 3; 8 - layer 4; 9 - layer 5; 10 - layer 6. The lateral geniculate body is the nucleus of the optic tubercle. The presence of six dark layers of a cluster of neurons is clearly visible, separated by light layers consisting of nerve fibers. Layers 1 and 2 are composed of large neurons (magnocellular), and layers 3-6 are composed of small cells (parvocellular)

for the reason that they consist of large neurons with an eccentrically located nucleus and a large amount of Nissl substance in the cytoplasm. The axons of the neurons of the magnocellular layer form not only visual radiance, but also go to the superior tubercles of the quadruple. The four outer layers are composed of small to medium sized cells (parvocellular layers, 3-6). They contain neurons that receive information from the retina and transmit it only to the visual cortex of the brain (form visual radiance). Neurons are also found that provide communication between neurons of the lateral geniculate body. These are the so-called "interneurons" (interneurons). It is believed that two layers of small neurons (parvocellular layers) appear in connection with the development of central vision.

It is important to note that fibers coming from different parts of the retina of both eyes are projected onto the listed layers of neurons. So, the crossed fibers of the optic tract end in the 1st, 4th and 6th layers, and the uncrossed ones - in the 2nd, 3 and 5th (Fig. 4.2.29). This occurs in such a way that the fibers from the corresponding parts of the two retinal halves (for example, the right temporal and left nasal halves of the retina) end in adjacent layers. The above features of projection onto the lateral geniculate body were established based on the use of various methods.

Chapter 4. BRAIN AND EYE

Rice. 4.2.29. Representation of the retina in the lateral geniculate body:

Impulses from corresponding points (a, b) two retinas pass into the optic tract. Uncrossed fibers (a ") end in layers 2, 3 and 5 of the lateral geniculate body. Crossed fibers (b") end in layers 1, 4 and 6. Impulses after passing Tubing(in ") are projected onto the cerebral cortex

research. So, in cases of destruction of the contralateral optic nerve or previous removal of the eyeball, degeneration of neurons of the 1st, 4th and 6th layers of the external geniculate body develops (Fig. 4.2.30). With the destruction of the homolateral fibers of the optic nerve, degeneration of neurons of the 2nd, 3rd and 5th layers occurs. This phenomenon is called transsynaptic degeneration. It has also been established that if the eyelids of one eye are sewn together at birth to a kitten, then after three months, 25-40% of the neurons of the lateral geniculate body will degenerate. This form of transsynaptic degeneration can explain some of the mechanisms of the development of amblyopia, which develops in congenital strabismus.

Experimental studies also indicate different projections of crossed and uncrossed fibers onto the lateral geniculate body. In these studies, a radioactive amino acid is injected into one of the eyeballs, which propagates transaxonally in the direction of the lateral geniculate body and accumulates in its neurons (Fig. 4.2.31).

Rice. 4.2.31. Distribution of a radioactive label in the external geniculate bodies after the introduction of a radioactive amino acid into the left eyeball of a monkey:

a- left lateral geniculate body; b - right lateral geniculate body. (The amino acid is absorbed by the retinal ganglion cells and transported along axons through the optic nerve, optic chiasm and optic tract to the lateral geniculate body. The illustration indicates that layers 2, 3, and 5 receive information from the ipsilateral eye, and layers 1, 4 and 6 from the contralateral eye)

Rice. 4.2.30. Changes in the microscopic structure of the lateral geniculate body on both sides when one eyeball is removed (by Alvord, Spence, 1997):

a- the external geniculate body (LCC), located ipsilaterally relative to the enucleated eye; b- tubing located contralateral to the enucleated eye. (After the death of the patient, whose eyeball was removed long before death, the external geniculate bodies were microscopically examined. After the disturbance of the normal projection of the retinal ganglion cells onto the neurons of the tubing, atrophy of the latter occurs. At the same time, the intensity of the staining of the layers decreases. The 1st and 5th tubing layers located ipsilaterally relative to the remote eye are much less stained with hematoxylin and eosin, while layers 3 and 5 of the tubing, located contralaterally relative to the remote eye, are colored more intensely than layers 4 and 6. It can also be noted that layers 1 and 2 are least affected)

Functional anatomy of the visual system

Features of the projection of the retina on the lateral geniculate body. Recently, the features of the projection of the retina on the lateral geniculate body have been revealed. They boil down to the fact that each point of half of the retina is accurately projected onto a specific point of the nucleus of the lateral geniculate body ("point to point"). Thus, spatial excitation in the layer of retinal ganglion cells is "mapped" by the spatial distribution of neuronal excitation in different layers of the lateral geniculate body. A strict topographic order of connections is also observed between cells of different layers. The projections of each point of the field of view in all layers are located directly one below the other, so that a columnar section can be distinguished, intersecting all layers of the lateral geniculate body and corresponding to the projection of the local area of ​​the field of view.

The given pattern of projection was revealed on the basis of experimental studies. Thus, it has been shown that local punctate damage to the retina leads to the development of transneural degeneration of small but well-defined cell clusters in three layers of the lateral geniculate body on both sides. Focal damage to the visual cortex or the introduction of a radioactive tracer into it leads to the "marking" of cells or fibers located in a line extending across all layers of the lateral geniculate body at the same level. These areas correspond to the "receptive fields" of the lateral geniculate body and are called the "projection column" (Fig. 4.2.32).

At this point in the presentation of the material, it is advisable to dwell on the features of the receptive fields of the lateral geniculate body. The receptive fields of the lateral geniculate body resemble those of the retinal ganglion cells. There are several main types of receptive fields. The first type is characterized by the presence of an ON response when the center is excited and an OFF response when the periphery is excited (ON / OFF type). The second type of receptive fields is characterized by an inverse relationship - OFF / ON-type. It is also characteristic of the lateral geniculate body that in layers 1 and 2 a mixture of receptive fields of the first and second types is found. At the same time, only one type of receptive fields is found in layers 3-6 (in two layers of the field of the first type, and in the other two - of the second type). Linear receptive fields with different ratios of ON- and OFF-centers are also found (Fig. 4.2.33). The use of electrophysiological methods made it possible to reveal that the receptive fields of the lateral geniculate body have a more pronounced opponent reaction than the receptive fields of the ganglion cells of the retina.

Lateral

Rice. 4.2.32. Schematic representation of parasagitis

tal cut of the lateral geniculate body. Projection

visual signal with the formation of a receptive

1t * - Back

* * * Z * x

Rice. 4.2.33. The structure of the receptive fields of the lateral geniculate body (a, b) and primary visual cortex (c-f) (after Hubel, Weisel, 1962):

a- ON-center receptive field of the lateral geniculate body; b- OFF-center receptive field of the lateral geniculate body; v-f- various options for the structure of simple receptive fields. (The crosses mark the fields corresponding to the ON-response, and the triangles - the OFF-response. The axis of the receptive field is marked by a solid line passing through the center of the receptive field)

chat rooms. This is what determines great importance the lateral geniculate body in enhancing the contrast. The phenomena of spatio-temporal summation of incoming signals, analysis of spectral characteristics of the signal, etc. have also been revealed. Neurons of the lateral geniculate body involved in color coding are localized in the parvocellular layers, where the

Chapter 4. BRAIN AND EYE

Cells are "red-green" and "blue-yellow" in color. As well as for retinal ganglion cells, they are characterized by linear summation of cone signals over the area of ​​the retina. Magnocellular layers also consist of opposing neurons with cone inputs spatially distributed in receptive fields. different types... It should be noted that anatomical segregation of neurons with different functional properties is observed already in the retina, where the processes of bipolar cells and ON- and OFF-types of ganglion cells are localized in different sublayers of the inner plexiform layer. This "anatomical isolation" of neuronal systems, which form different channels of information transmission, is a general principle in the construction of analyzer structures and is most pronounced in the columnar structure of the cortex, which we will discuss below.

Retina

the outer part of the external geniculate body (Fig. 4.2.29). The macular region of the retina is projected onto a wedge-shaped sector located in the posterior two-thirds or three-quarters of the lateral geniculate body (Fig. 4.2.34, 4.2.35).

It is noted that the representation of the visual half-fields in the visual tract, as it were, "turns" at the level of the lateral geniculate body in such a way that the vertical section becomes horizontal. In this case, the upper part of the retina is projected onto the medial part, and the lower part is projected onto the lateral part of the lateral geniculate body. This rotation is completely altered in visual radiance so that when the fibers reach the visual cortex, the quadrant of the upper retina is at the top of the tract and the lower quadrant is at the bottom.

External geniculate body

Rice. 4.2.34. Projection of the retina onto the lateral geniculate body: / ​​- macula; 2 - monocular crescent

s r Yaa

Continuing the description of the features of the projection of the retina onto the lateral geniculate body, it should be noted that the peripheral temporal areas of the retina of the opposite eye are projected onto layers 2, 3 and 5 and are called the monocular crescent.

The most complete data on the retinotopic organization of optic nerve fibers, optic chiasm and nuclei of the lateral geniculate body in humans and monkeys were obtained by Brouewer, Zeeman, Polyak, Hoyt, Luis. We will first describe the projection of the non-macular fibers. Noncrossing fibers coming from the superior temporal quadrant of the retina are located dorso-medially in the optic chiasm and are projected onto the medial part of the nucleus of the lateral geniculate body. Noncrossing fibers extending from the inferior temporal quadrant of the retina are located in the optic chiasm below and laterally. They are projected onto

Rice. 4.2.35. Schematic representation of a coronary

a cut through the lateral geniculate body (rear view)

(after Miller, 1985):

Attention is drawn to the large representation in the lateral geniculate body of the macular region (1-6 numbers of tubing layers)

Functional anatomy of the visual system

Synaptic interactions of neurons of the lateral geniculate body. Previously, it was assumed that the axon of the ganglion cell is in contact with only one neuron of the lateral geniculate body. Thanks to electron microscopy, it was found that afferent fibers form synapses with several neurons (Fig. 4.2.36). At the same time, each neuron in the lateral geniculate body receives information from several retinal ganglion cells. On the basis of ultrastructural studies, various synaptic contacts between them were also revealed. The axons of ganglion cells can end both on the body of the neurons of the lateral geniculate body, and on their primary or secondary dendrites. In this case, the so-called "ball-barrel" endings are formed (Fig. 4.2.37, see col. incl.). In cats, the "glomeruli" are separated from the surrounding formations by a thin capsule consisting of processes of glial cells. This isolation of the "glomeruli" is absent in monkeys.

Synaptic "glomeruli" contain synapses of axons of retinal ganglion cells, synapses of neurons of the lateral geniculate body and interneurons ("interneurons"). These synaptic structures resemble retinal “triads”.

Each "glomerulus" consists of a zone of densely packed neurons and their terminals. In the center of this zone is the axon of the ganglion

Rice. 4.2.36. Schematic representation of the interaction of the terminals of the axons of retinal ganglion cells with neurons of the lateral geniculate body in a monkey (after Glees, Le Gros, Clark, 1941):

optic nerve bundle (a) enters the cell layer (b) of the lateral geniculate body (LCC) on the right. Some fibers give off 5-6 branches, approach the body of tubing neurons and form a synapse. Axons of tubing cells (c) leave the cell layer of tubing, pass through the fibrous layer and form visual radiance

retinal cells, which is presynaptic. It forms synapses with a neuron of the lateral geniculate body and intercalary neurons. The dendrites of the neurons of the lateral geniculate body enter the "glomeruli" in the form of a thorn, which directly forms a synapse with the retinal axon. The dendrite of interneurons (interneurons) forms a synapse with an adjacent "glomerulus", forming consecutive synapses between them.

Lieberman distinguishes pre- and postsynaptic “inhibitory” and “excitatory” dendritic and “glomerular” synapses. They are a complex collection of synapses between axons and dendrites. It is these synapses that structurally provide the phenomenon of inhibition and excitation of the receptive fields of the external geniculate body.

External crank functions body. It is assumed that the functions of the lateral geniculate body include: enhancement of image contrast, organization of visual information (color, movement, shape), modulation of the level of processing of visual information with their activation (through the reticular formation). It has an external geniculate body and binocular receptive fields. It is important to note that the functions of the lateral geniculate body are also influenced by the higher centers of the brain. Confirmation of the role of the lateral geniculate body in the processing of information coming from the higher parts of the brain is the detection of a projection onto it efferent fibers, emanating from the cerebral cortex. They arise in layer VI of the visual cortex and are projected onto all layers of the lateral geniculate body. For this reason, minor damage to the visual cortex causes neuronal atrophy in all six layers of the lateral geniculate body. The terminals of these fibers are small and contain numerous synaptic vesicles. They end both on the dendrites of the neurons of the lateral geniculate body, and on the interneurons ("interneurons"). It is assumed that, through these fibers, the cerebral cortex modulates the activity of the lateral geniculate body. On the other hand, it has been shown that changes in the activity of neurons in the lateral geniculate body selectively activate or inhibit neurons in the visual cortex of the brain.

There are other connections of the lateral geniculate nucleus. This is a connection with the cushion of the optic tubercle, the ventral and lateral nuclei of the optic tubercle.

Blood supply to the lateral geniculate body carried out by the posterior cerebral and posterior villous arteries (Fig. 4.2.38). The main vessel supplying blood to the external geniculate body, especially the posterior-not-internal surface of it, is the posterior

Chapter 4. THE BRAIN AND THE EYE

90 80 70 60150 40 30 20-10

Rice. 4.2.38. Arterial blood supply to the surface of the lateral geniculate body:

/ - anterior villous (choroidal) artery; 2 - villous plexus; 3 - the leg of the brain; 4 - the gate of the external geniculate body; 5 - external geniculate body; 6 - the medial geniculate body; 7 - the oculomotor nerve; 8 - the nucleus of the oculomotor nerve; 9 - posterior cerebral artery; 10 - posterior villous artery; // - black substance

nyaya cerebral artery. In some cases, a branch departs from this artery - the posterior villous (choroidal) artery. In case of impaired blood circulation in this artery, violations of the field of the upper homonymous quadrant of the retina are found.

The anterior villous (choroidal) artery almost completely supplies the anterior and lateral surfaces of the lateral geniculate body. For this reason, impaired blood circulation in it leads to damage to the fibers emanating from the lower quadrant of the retina (Fig. 4.2.39). This artery departs from the internal carotid artery (sometimes from the middle cerebral artery) just distal to the exit site of the posterior communicating artery. Upon reaching the anterior part of the lateral geniculate body, the anterior villous artery gives off a different number of branches before entering the inferior horn of the lateral ventricle.

The part of the lateral geniculate body, onto which the fibers emanating from the macula are projected, is supplied with blood by both the anterior and posterior villous arteries. In addition, from a well-developed system of anastomoses located in the soft and arachnoid membranes of the brain, numerous arterioles depart, penetrating into the lateral geniculate body. There they form a dense network of capillaries in all its layers.

^ - ^ - ^ Horizontal meridian of the field of view - - - - - Lower oblique meridian of the field of view

I I Territory of the anterior villous artery VIV Territory of the external villous artery

Rice. 4.2.39. Scheme of blood supply to the right lateral geniculate body and features of visual field loss (homonymous visual field defect) resulting from circulatory disorders in the pool of the villous (choroidal) artery (by Frisen et al., 1978):

a- retina; b- the external geniculate body (/ - anterior villous artery; 2 - medial surface; 3 - lateral surface; 4 - posterior villous artery; 5 - posterior artery brain)

Functional anatomy of the visual system

4.2.6. Visual radiance

Visual radiance (radiatio optica; Grasiole, Gratiolet) is analogous to other lu-clears of the visual hillock, such as the auditory, occipital, parietal and frontal. All of the above radiations pass through the inner capsule connecting the cerebral hemispheres and

stem part of the brain, spinal cord... The inner capsule is located lateral to the optic tubercle and lateral ventricles of the brain and medial to the lenticular nucleus (Fig. 4.2.40, 4.2.41). The posterior part of the inner capsule contains fibers of auditory and visual radiance and descending fibers extending from the occipital cortex to the superior tubercles of the quadruple.

10

and

16

17

Rice. 4.2.41. Horizontal section of the brain at the level of the location of the visual radiance:

/ - spur groove; 2 - visual radiance; 3 - inner capsule; 4 - outer capsule; 5 - fourth ventricle;

6 - a plate of a transparent partition;

7 - anterior horn of the lateral ventricle; 8 -
longitudinal slit of the brain; 9 - knee mozo
leafy body; 10 - transparent ne cavity
regorods; // - the head of the caudate nucleus;
12 - fence; 13 - shell; 14 - pale
ball; 15 - visual hillock; 16 - hippo
camp; 17 - back knee of the lateral stomach
daughter

Chapter 4. THE BRAIN AND EYE

Visual radiance connects the external geniculate body with the cortex of the occipital lobe of the brain. In this case, the course of the fibers emanating from different parts of the lateral geniculate body is quite different. So, the fibers coming from the neurons of the lateral part of the lateral geniculate body bend around the lower horn of the lateral ventricle, located in the temporal lobe, and then, going posteriorly, pass under the posterior horn of this ventricle, reaching the lower parts of the visual cortex, near the groove (Fig. 4.2 .40, 4.2.41). Fibers from the medial part of the lateral geniculate body go a slightly more direct path to the primary visual cortex (field 17 according to Brodman), located in the medial part of the occipital lobe. The fibers of this pathway deviate laterally, passing directly anterior to the entrance to the lateral ventricle, and then turn posteriorly, go in the caudal direction, bending from above the posterior horn of this ventricle and end in the cortex located along the upper edge of the groove.

The superior fibers leaving the lateral geniculate body travel directly to the visual cortex. The lower fibers make a loop around the ventricles of the brain (Meer's loop) and go to the temporal lobe. The lower fibers are tightly attached to the sensory and motor fibers of the inner capsule. Even a small stroke that occurs in this area leads to upper hemianopsic visual field defects and hemiparesis (contralateral).

The most anterior fibers are found approximately 5 hedgehogs behind the apex of the temporal lobe. It has been noted that lobectomy, in which the brain tissue is excised 4 cm from the apex of the temporal lobe, does not lead to the appearance of a visual field defect. In case of damage to a larger area (deeply located tumors, temporal decompression due to injury, or infectious disease) develop homonymous upper quadrant hemianopsia. The most typical forms of visual field defect with damage to visual radiance are shown in Fig. 4.2.19, 4.2.43.

As indicated above, visual radiance contains 3 main fiber groups. The upper part contains the fibers serving the lower fields of view, the lower part contains the upper fields. The central part contains macular fibers.

The retinotopic organization of the fibers of the lateral geniculate body extends to visual radiance, but with some changes in the position of the fibers (Fig. 4.2.42). The dorsal bundle of fibers, representing the upper peripheral quadrant of the retina, originates from the medial part of the lateral geniculate body and extends to the dorsal lip of the avian

whose spurs. The ventral fiber bundle represents the periphery of the inferior quadrant of the retina. It passes in the lateral part of the lateral geniculate body and approaches the ventral lip of the avian spur. It is assumed that these projections of the retinal periphery lie in the visual radiance of the medial projection of the macular fibers. Macular fibers spread forward, occupying the greater central part of the visual radiance in the form of a wedge. Then they are directed posteriorly and converge in the region of the upper and lower lips of the bird's spur.

As a result of the separation of peripheral and central projections, damage to visual radiance can lead to quadrant drops in the visual field with a clear horizontal border.

The most peripherally located nasal projections of the retina, representing a "monocular crescent", are collected near the upper and lower boundaries of the dorsal and ventral bundles of visual radiance.

Disturbances in the field of visual radiance lead to a number of specific disturbances in the visual fields, some of which are shown in Fig. 4.2.43. The nature of the loss of the visual field is largely determined by the level of damage. The reason for such violations may be different

External geniculate body

(3(3

oo

Rice. 4.2.43. Diagram of fiber propagation in the optic tract, lateral geniculate body and visual radiance. Violation of the visual field in case of damage to the areas located after the optic chiasm:

/ - compression of the optic tract - homonymous hemianopsia with a fuzzy edge; 2 - compression of the proximal part of the optic tract, the lateral geniculate body or the lower part of the visual radiance - homonymous hemianopsia without preserving the macular field with a clear edge; 3 - compression of the anterior loop of visual radiance - upper quadrant anopsy with indistinct edges; 4 - compression of the upper part of the visual radiance - lower quadrant anopsia with indistinct edges;

5 - compression of the middle part of the visual radiance - homonym
naya hemianopsia with fuzzy edges and central prolapse
th vision; 6 - compression of the back of the visual radiance -
congruent homonymous hemianopsia with central preservation
vision; 7 - compression of the anterior part of the bark in the area of ​​the shp
ry - temporal loss of the field of view from the opposite
parties; 8 - compression of the middle part of the bark in the spur area -
homonymous hemianopsia with preservation of central vision with
the side of the lesion and the preservation of the temporal field of view with
opposite side; 9 - compression of the posterior part of the cortex behind
the posterior region - congruent homonymous hemianopsic

kaya scotoma

no-like diseases of the brain. Most often it is a circulatory disorder (thrombosis, embolism in hypertension, stroke) and tumor development (glioma).

Due to the fact that a violation of the structure and function of visual radiance is often associated with impaired blood circulation, it is important to know

06 features of the blood supply to this area.
Blood supply of visual radiance

carried out on 3 levels (fig. 4.2.24):

1. Part of the visual radiance, passing
shi laterally and above the lower horn of the lateral
ventricle, blood is supplied by the branch of the anterior
villous (choroidal) artery.

2. Part of the visual radiance, located
venous behind and lateral to the horn of the ventricle
ka, blood is supplied by the deep ocular branch
middle cerebral artery. The last one

flows into this area through the anterior perforated substance together with the lateral banded arteries.

3. When the visual radiance approaches the cerebral cortex, the blood supply is carried out by the perforating arteries of the cortex, mainly by the branches of the artery of the avian spur. The avian spur artery extends from the posterior cerebral artery, and sometimes from the middle cerebral artery.

All perforating arteries belong to the so-called terminal arteries.

Visual cortex

As mentioned above, the systems of neurons in the retina and the lateral geniculate body analyze visual stimuli, assessing their color characteristics, spatial contrast, and average illumination in different parts of the visual field. The next stage in the analysis of afferent signals is performed by a system of neurons in the primary visual cortex. (visul cortex).

The identification of the areas of the cerebral cortex responsible for the processing of visual information has its own rather long history. Back in 1782, medical student Francesco German described a white streak running through the gray matter of the occipital lobe. It was he who first suggested that the cortex could contain anatomically different areas. Prior to Gennari's discovery, anatomists assumed that the cortex was a homogeneous plate of tissue. Gennari had no idea that he had stumbled upon the primary visual cortex. It took over a century for Henschen to prove that the Gennari stripe corresponds to the primary visual cortex.