The value of the nuclei of the medial and lateral geniculate bodies. Signal coding in the lateral geniculate body and primary visual cortex Lateral geniculate body
Outland or metathalamus
Metathalamus (Latin Metathalamus) is a part of the thalamic region of the mammalian brain. Formed by paired medial and lateral geniculate bodies lying behind each thalamus.
The medial geniculate body is located behind the cushion of the thalamus, it, along with the lower hillocks of the roof plate of the midbrain (quadruple), is the subcortical center of the auditory analyzer. The lateral geniculate body is located downward from the pillow. Together with the upper mounds of the roof plate, it is the subcortical center of the visual analyzer. The nuclei of the geniculate bodies are connected by pathways with the cortical centers of the visual and auditory analyzers.
In the medial part of the thalamus, a mediodorsal nucleus and a group of midline nuclei are distinguished.
The mediodorsal nucleus has bilateral connections with the olfactory cortex of the frontal lobe and the cingulate gyrus of the cerebral hemispheres, the amygdala and the anteromedial nucleus of the thalamus. Functionally, it is also closely associated with the limbic system and has two-way connections with the cortex of the parietal, temporal and insular lobes of the brain.
The mediodorsal nucleus is involved in the implementation of higher mental processes. Its destruction leads to a decrease in anxiety, anxiety, tension, aggressiveness, and the elimination of obsessive thoughts.
The nuclei of the midline are numerous and occupy the most medial position in the thalamus. They receive afferent (i.e., ascending) fibers from the hypothalamus, from the nuclei of the suture, the blue spot of the reticular formation of the brainstem, and partly from the spinal thalamic tract in the medial loop. Efferent fibers from the midline nuclei are directed to the hippocampus, amygdala and cingulate gyrus of the cerebral hemispheres, which are part of the limbic system. Connections with the cerebral cortex are bilateral.
The nuclei of the midline play an important role in the processes of awakening and activation of the cerebral cortex, as well as in providing memory processes.
In the lateral (i.e. lateral) part of the thalamus, the dorsolateral, ventrolateral, ventral posteromedial and posterior groups of nuclei are located.
The nuclei of the dorsolateral group are relatively poorly understood. They are known to be involved in the pain perception system.
The nuclei of the ventrolateral group differ anatomically and functionally. The posterior nuclei of the ventrolateral group are often considered as one ventrolateral nucleus of the thalamus. This group receives fibers of the ascending path of general sensitivity as part of the medial loop. Fibers of gustatory sensitivity and fibers from the vestibular nuclei also come here. Efferent fibers, starting from the nuclei of the ventrolateral group, are sent to the cortex of the parietal lobe of the cerebral hemispheres, where they conduct somatosensory information from the whole body.
To the nuclei of the posterior group (nucleus of the thalamic cushion) there are afferent fibers from the upper hillocks of the quadruple and fibers in the optic tract. Efferent fibers are widely distributed in the cortex of the frontal, parietal, occipital, temporal and limbic lobes of the cerebral hemispheres.
Nuclear centers of the thalamus cushion are involved in the complex analysis of various sensory stimuli. They play a significant role in the perceptual (associated with perception) and cognitive (cognitive, mental) activity of the brain, as well as in the processes of memory - storage and reproduction of information.
Intralaminar group of thalamic nuclei lies in the thickness of the vertical Y-shaped layer of white matter. Intralaminar nuclei are interconnected with the basal nuclei, the dentate nucleus of the cerebellum and the cerebral cortex.
These nuclei play an important role in the brain's activation system. Damage to the intralaminar nuclei in both thalamuses leads to a sharp decrease in motor activity, as well as apathy and destruction of the motivational structure of the individual.
The cerebral cortex, due to bilateral connections with the thalamic nuclei, is able to exert a regulatory effect on their functional activity.
Thus, the main functions of the thalamus are:
processing of sensory information from receptors and subcortical switching centers with its subsequent transfer to the cortex;
participation in the regulation of movements;
ensuring communication and integration of various parts of the brain
Lateral geniculate body
Lateral geniculate body(lateral geniculate body, LCT) is an easily recognizable structure of the brain, which is located on the lower lateral side of the thalamic cushion in the form of a fairly large flat tubercle. In the LCT of primates and humans, six layers are morphologically defined: 1 and 2 - layers of large cells (magnocellular), 3-6 - layers of small cells (parvocellular). Layers 1, 4, and 6 receive afferents from the contralateral (located in the opposite hemisphere of the LCT) eye, and layers 2, 3, and 5 from the ipsilateral (located in the same hemisphere as LCT).
Schematic diagram of primate LCT. Layers 1 and 2 are located more ventrally, closer to the incoming fibers of the optical path.
The number of LCT layers involved in processing the signal coming from the retinal ganglion cells is different depending on the eccentricity of the retina:
- - at eccentricity less than 1º, two parvocellular layers are involved in the treatment;
- - from 1º to 12º (blind spot eccentricity) - all six layers;
- - from 12º to 50º - four layers;
- - from 50º - two layers associated with the contralateral eye
There are no binocular neurons in the LBT of primates. They appear only in the primary visual cortex.
Literature
- Hubel D. Eye, brain, vision / D. Hubel; Per. from English O. V. Levashova and G. A. Sharaeva. - M .: "Mir", 1990. - 239 p.
- Morphology of the nervous system: Textbook. allowance / D. K. Obukhov, N. G. Andreeva, G. P. Demyanenko and others; Resp. ed. V.P. Babmindra. - L .: Nauka, 1985. - 161 p.
- Erwin E. Relationship between laminar topology and retinotopy in the rhesus lateral geniculate nucleus: results from a functional atlas / E. Erwin, F.H. Baker, W.F. Busen et al. // Journal of Comparative Neurology. 1999. Vol.407, No. 1. P.92-102.
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See what the "Lateral geniculate body" is in other dictionaries:
Lateral geniculate body- two cell nuclei of the thalamus, located at the ends of each of the optical tracts. Paths from the left side of the left and right retina go to the left body, to the right, respectively, the right side of the retina. From here, the visual pathways are directed to ... ... encyclopedic Dictionary in psychology and pedagogy
Lateral geniculate body (LCT)- The main sensory center of vision, located in the thalamus, a part of the brain that plays the role of the main switching device in relation to incoming sensory information. Axons emanating from the LCT enter the visual zone of the occipital lobe of the cortex ... Psychology of Sensations: Glossary
lateral geniculate body- (c. g. laterale, PNA, BNA, JNA) K. t., lying on the lower surface of the thalamus laterally from the handle of the upper hillock of the quadruple: the location of the subcortical center of vision ... Comprehensive Medical Dictionary
Visual system- Pathways of the visual analyzer 1 Left half of the visual field, 2 Right half of the visual field, 3 Eye, 4 Retina, 5 Optic nerves, 6 Eyes ... Wikipedia
Brain structures- Human brain reconstruction based on MRI Contents 1 Brain 1.1 Prosencephalon (forebrain) ... Wikipedia
Visual perception
Vision- Pathways of the visual analyzer 1 Left half of the visual field, 2 Right half of the visual field, 3 Eye, 4 Retina, 5 Optic nerves, 6 Oculomotor nerve, 7 Chiasm, 8 Optic tract, 9 Lateral geniculate body, 10 ... ... Wikipedia
Viewer- Pathways of the visual analyzer 1 Left half of the visual field, 2 Right half of the visual field, 3 Eye, 4 Retina, 5 Optic nerves, 6 Oculomotor nerve, 7 Chiasm, 8 Optic tract, 9 Lateral geniculate body, 10 ... ... Wikipedia
Human visual system- Pathways of the visual analyzer 1 Left half of the visual field, 2 Right half of the visual field, 3 Eye, 4 Retina, 5 Optic nerves, 6 Oculomotor nerve, 7 Chiasm, 8 Optic tract, 9 Lateral geniculate body, 10 ... ... Wikipedia
Visual analyzer- Pathways of the visual analyzer 1 Left half of the visual field, 2 Right half of the visual field, 3 Eye, 4 Retina, 5 Optic nerves, 6 Oculomotor nerve, 7 Chiasm, 8 Optic tract, 9 Lateral geniculate body, 10 ... ... Wikipedia
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 the 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 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 rest of the 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.
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.
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. At the same time, both branches retain their retinotopic specificity, that is, they arrive at 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. Large sizes This formation allows one to think that it performs some special functions in a person, 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.
retinal brain occipital visual
represents a small oblong eminence at the postero-inferior 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 over time, according to which both the external geniculate body and the pulvinar and anterior quadruple were considered primary visual centers.
At present, 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 from embryology and comparative anatomy, does not allow us to attribute the role of the primary visual center to pulvinar. So, according to Genshen's observations, in the presence of pathological changes in the pulvinar, the field of vision remains normal. Browver notes that with an altered 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, at postmortem examination, he found limited changes in the dorsal part of the lateral geniculate body.
Ronne, with atrophy of the optic nerves with central scotomas due to alcohol intoxication, found limited changes in ganglion cells in the external geniculate body, indicating that the macular region is projected onto the dorsal part of the 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 mentioned by us made it possible to study to some extent the projection of the retina in the lateral geniculate body. They found that most of the lateral geniculate body is occupied by the projection of the retinal regions involved in the binocular act of vision. The extreme periphery of the nasal half of the retina, corresponding to the monocularly perceived temporal half moon, is projected onto a narrow zone in the ventral part of the lateral geniculate body. The macular projection 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. 9. 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... Minkowski discovered at the same time characteristic feature: in both geniculate bodies, atrophy with a certain pattern spreads 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 ganglion cell layers, as is well illustrated in Le Gros Clark's diagram (Fig. 10).
Rice. 10. Scheme of the end of the fibers of the optic tract and the beginning of the fibers of the 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 bundle; 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 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. One eye was removed from a 50-year-old patient 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.