Outer geniculate body
The axons of the optic tract approach one of the four second-order receptive and integrating centers. The nuclei of the lateral geniculate body and superior tubercles of the quadrigemina are the target structures most important for visual function. The geniculate bodies form a "knee-like" bend, and one of them - lateral (ie, lying further from the median plane of the brain) - is associated with vision. The tubercles of the quadrigemina 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.
Superior tubercles of the quadrigemina. Many ganglion cell axons branch before reaching the lateral geniculate nucleus. While one branch connects the retina to this nucleus, the other goes to one of the secondary level neurons in the superior colliculus. As a result of this branching, two parallel paths are created from the ganglion cells of the retina to two different centers of the thalamus. At the same time, both branches retain their retinotopic specificity, i.e., they come to points that together form an ordered projection of the retina. The superior colliculus neurons, which receive signals from the retina, send their axons to a large nucleus in the thalamus called the pillow. This nucleus becomes larger in the series of mammals as their brains become more complex and reaches greatest development in a person. Large sizes This formation allows us to think that it performs some special functions in a person, but its true role remains unclear. Along with the primary visual signals, the neurons of the superior colliculi receive information about sounds coming from certain sources and about the position of the head, as well as processed visual information returning through the feedback loop from the neurons of the primary visual cortex. On this basis, it is believed that the hillocks serve as the primary centers for integrating information that we use 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. According to their shape, the neurons of the visual cortex are divided into large and small, stellate, bushy, fusiform.
The famous neuropsychologist Lorente de No in the 40s. of 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 axodendrial, terminal and collateral, they can be divided into two types: 1) synapses with a large extent and multiple synaptic endings and 2) synapses with a small extent 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, the reticular formation, the 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 features of the visual signal (the selection of contours, outlines, the shape of an object, etc.) is carried out. 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
Signal encoding in the lateral geniculate body and primary visual cortex
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 "zone 17" or the striate cortex. 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 have been described in area V 1 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 continuing each other research in the field of 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 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 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 in order to understand the functioning of any part nervous system knowledge is needed about the properties of its constituent neurons: 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 most simple task or an event involving hundreds of thousands nerve cells located in various parts 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 repeating structure nervous tissue 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 layers of cells (A, A 1 , C) can be seen, one of which (A 1) has complex structure and subdivided further. 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, 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). 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. 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 area 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, nevertheless, each LC neuron receives convergent signals from several fibers of the optic nerve. 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 antagonizing 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 functioning 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. 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 similar 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. 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 manner. 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 (under the appropriate angle to the surface). Conversely, many (but not all) of their lateral processes are short. Connections between primary visual cortex and cortex higher order carried out by means of 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. 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 pulvinar zone 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. 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 the concept of cortical columns developed by Mountcastle 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 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.
Maps of visual fields in the lateral geniculate body
Functional layers of LCT
Cytoarchitectonics of the visual cortex
Incoming, outgoing pathways and layered organization of the cortex
Separation of incoming fibers from LQT in layer 4
Similar works to - Signal coding in the lateral geniculate body and primary visual cortex
1. Receptor potential of rods and cones. The current of ions 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 signaling pathway from photoreceptors to the ganglion cell. Indirect signaling pathway.
4. Receptive fields with on-centers and off-centers. On-neurons. Off-neurons. Ganglion cell on-type. Off-type ganglion cell.
5. Receptive fields of color perception. Color perception. primary colors. Monochromatic. Dichromasia. Trichromasia.
6. M- and P-types of retinal ganglion cells. Magnocellular (M-cells) cells. Parvocellular (P-cells) ganglion cells of the retina.
7. Pathways and centers of the visual system. 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. Projective visual cortex. Light edge. complex neurons. Double anticolor cells.
10. Visual perception. magnocellular pathway. parvocellular pathway. Perception of form and 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 retinal M-cells, with 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 retinal P-cells: 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, i.e., left and right, six neural maps located exactly one above the other of the opposite half of the visual field are formed. Neural maps are organized retinotopically, in each of them about 25% of the cells receive information from the photoreceptors of the fovea.
Receptive fields of neurons of the lateral geniculate body have a rounded shape with on- or off-type centers and 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 almost does not change here. Signals from parvocellular and magnocellular cells of the retina are processed independently of each other and transmitted to the visual cortex in parallel pathways. Neurons lateral geniculate body receive no more than 20% of afferent inputs from the retina, 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.
The lateral geniculate bodies are signal switches from the anterior colliculus.
Olfactory and visceral reception is transmitted through the anterior nuclei of the thalamus to the limbic zone of the cerebral cortex. The areas of visceral reception are located in morphological proximity to the nuclei that receive signals from exteroceptors. Hence the appearance of the so-called reflected pain. It is known that diseases of the internal organs cause a painful increase in the sensitivity of certain areas of the skin. So, pain in the heart associated with an attack of angina, "give" to the left shoulder, under the shoulder blade.
The ventrolateral nuclei serve as signal switches from the brainstem and cerebellum to the anterior central gyrus of the cerebral cortex. The posterior ventral nucleus receives impulses from the lemniscal sensory pathway, which carries signals from the Gol and Burdach nuclei of the medulla oblongata and the spinal-thalamic pathway. From here they go to the posterior central gyrus of the cerebral cortex.
The associative nuclei of the thalamus are located mainly in its anterior part (pillow nucleus, dorsal and lateral nuclei). They transmit impulses from the switching nuclei to the association zones of the cortex. The thalamus also functions as a subcortical pain center. In its nuclei, information is processed from receptors and pain sensations are formed.
"Human Physiology", N.A. Fomin
The subcortical nuclei include the caudate nucleus, the globus pallidus, and the shell. They are located in the thickness of the cerebral hemispheres, between the frontal lobes and the diencephalon. The embryonic origin of the caudate nucleus and the shell is one, therefore they are sometimes spoken of as a single striatum (striatum). The pale ball, phylogenetically the most ancient formation, is isolated from the striatum and morphologically, ...
Irritation of the pale ball causes slow tonic contractions of the skeletal muscles. The pale ball acts as a collector connecting the striatum with the nuclei of the hypothalamus, brain stem and thalamus. An important role belongs to the pale ball and in the regulation of hemodynamics. The destruction of the striatum causes in animals a decrease in sensitivity to tactile and pain stimuli. Orienting reflexes are lost, "emotional dullness" appears. Memorization processes are disrupted: ...
Corticoreticular connections: A - scheme of pathways of ascending activating influences; B - scheme of descending influences of the cortex; Cn - specific afferent pathways to the cortex with collaterals to the reticular formation (according to Magun). The brain and spinal cord carry out two forms of regulatory influences: specific and nonspecific. A specific regulatory system includes nerve pathways that conduct efferent impulses from all receptors, centers ...
The reticular formation increases the excitability of motor neurons spinal cord that regulate the activity of muscle spindles. As a result, muscle spindles send a constant stream of impulses to the spinal cord and excite α-motor neurons. In turn, the flow of impulses from α-motor neurons maintains a constant tone of skeletal muscles. Regulatory tonic influences come from the tegmentum of the brain along two pathways of the reticulospinal tract, which conduct nerve signals from different ...
The cerebellum coordinates complex motor acts and voluntary movements. The efferent influences of the cerebellum through the upper legs are directed to the red nucleus of the midbrain, to the nuclei of the thalamus and hypothalamus, to the subcortical nodes and to the motor zone of the cerebral cortex. The cerebellum regulates the activity of the motor neurons of the spinal cord through the red-nuclear-spinal pathway. Afferent impulses enter the cerebellum through the lower and middle legs. By…
