Limbic system of the brain

The cortical zones of the olfactory analyzer (hippocampus - gyrus hippocampi, transparent septum pellucidum, gyrus cinguli girdle, etc.), and partly the taste analyzer (circular isthmus of the islet) are now referred to the limbic region of the cerebral hemispheres. These parts of the cortex are connected with other medio-partal areas of the temporal and frontal lobes, with the formation of the hypothalamus and the reticular formation of the brain stem. The listed formations are united by numerous bilateral relations into a single limbico-hylotal-reticular complex, which plays a major role in the regulation of all vegetative-visceral functions of the body. The oldest sections of the cerebral cortex that enter this complex, in their cytoarchitectonics (three-layered type of cellular structure) differ from the rest of the cortex, which has a six-layered type of structure.

R.Vgosa (1878) considered phylogenetically old telencephalic regions located around the brain stem as a "large limbic lobe".

These same structures were referred to as the "olfactory brain," which does not reflect their leading role in organizing complex behavioral acts. The identification of the role of these formations in the regulation of vegetative-visceral functions led to the emergence of the term "visceral brain" [McLean P., 1949]. Further refinement of the anatomical and functional features and the physiological role of these structures led to the use of a less specific definition - the "limbic system." The limbic system includes anatomical formations that are interconnected by close functional links.The structures that make up the limbic system differ in the phylogenetic plan:

• ancient cortex (paleocortex) - hippocampus, pyriform gyrus, pyriform, periamigdalar cortex, entorhinal region, olfactory bulb, olfactory tract, olfactory tubercle;
• parallocortex - the area occupying an intermediate position between the old and the new cortex (the gyrus of the gyrus, or the limbic lobe, the precubiculum, the frontal parietal cortex);
• subcortical formations - almond-shaped complex, septum, anterior thalamus nuclei, hypothalamus;
• reticular formation of the midbrain.

The central links of the limbic system are the amygdala complex and the hippocampus.

The tonsil receives afferent impulses from the olfactory tubercle, septum, piriform cortex, temporal pole, temporal gyri, orbital cortex, anterior part of the islet, intralaminar nuclei of the thalamus, anterior part of the hypothalamus and the reticular formation.

Efferent pathways are two: dorsal - through stria terminalis in the anterior hypothalamus and ventral - in the subcortical formations, temporal cortex, islet and along the polysynaptic path to the hippocampus.

To the hippocampus, afferent impulses come from the anterolateral basal structures, the frontotemporal cortex, the islet, the cingular groove, from the septum through Brock's diagonal ligament, connecting the reticular formation of the midbrain to the hippocampus.

The efferent path from the hippocampus goes through the arch to the mamillary bodies, through the mastoid-thalamic fascicle (the bundle of Wick-d'Azir) to the anterior and intralaminar nuclei of the thalamus, then to the midbrain and the bridge of the brain.

The hippocampus is closely related to other anatomical structures entering the limbic system, and forms with them a Papetz circle [Papez J., 1937]: the hippocampus-vault-septum-mamillary bodies-the anterior thalamus nuclei-the gyrus-the hippocampus.

Thus, there are two main functional neuronal circles of the limbic system: a large circle of Pape and a small circle, including the amygdala complex - stria terminalis - the hypothalamus.

There are several classifications of limbic structures. According to the anatomical classification N. Gastaut, N. Lammers (1961) distinguish two parts - basal and limbic; according to the anatomical and functional classification - the oromedial-basal area regulating vegetative-visceral functions, behavioral acts associated with the food function, the sexual and emotional sphere, and the posterior region (the posterior part of the cingular furrow, the hippocampal formation) that participates in the organization of more complex behavioral acts, and mnestic processes. P. McLean identifies two groups of structures: the growth (orbital and islet cortex, the temporal pole cortex, pear-shaped lobe), ensuring the preservation of life for this individual, and the caudal (septum, hippocampus, lumbar gyrus), which ensures the preservation of the species as a whole, regulating generative functions.

K. Pribram, L. Kruger (1954) identified three subsystems. The first subsystem is considered as the primary olfactory (olfactory bulb and tubercle, diagonal fascicle, corticomedial nuclei of the amygdala), the second provides olfactory-taste perception, metabolic processes and emotional reactions (septum, basal-lateral nuclei of the amygdala, frontotemporal basal cortex) and the third participates in emotional reactions (hippocampus, entorhinal cortex, girdle gyrus). Phylogenetic classification [Falconner M., 1965] also distinguishes two parts: the old one, consisting of mamillary structures closely associated with the midline and neocortex formations, and later - the temporal neocortex. The first carries out vegetative-endocrine-somatoemotional correlations, the second - interpretive functions. According to the concept of K. Lissak, E. Grastian (1957), the hippocampus is regarded as a structure that has inhibitory effects on the thalamocortical system. At the same time, the limbic system plays an activating and modeling role in relation to a number of other brain systems.

The limbic system participates in the regulation of vegetative-visceral-hormonal functions aimed at providing various forms of activity (food and sexual behavior, species conservation processes), in the regulation of sleep and wakefulness systems, attention, emotional sphere, memory processes, thus providing somatovegetative integration.

Functions in the limbic system are represented globally, topographically poorly differentiated, but certain departments have relatively specific tasks in the organization of holistic behavioral acts. Including neuron closed circles, this system has a large number of "inputs" and "outputs" through which its afferent and efferent connections are realized. 

The defeat of the limbic hemisphere causes primarily a variety of disorders of vegetative-visceral functions. Many of these violations of the central regulation of autonomic functions, which were previously attributed only to the pathology of the hypothalamic region, are associated with lesions of the limbic region, especially the temporal lobes.

The pathology of the limbic part can be manifested by symptoms of prolapse with vegetative asymmetry or symptoms of irritation in the form of vegetative-visceral seizures, a bowl of temporal, less often frontal origin. Such attacks are usually less prolonged than hypothalamic; they can confine themselves to short auras (epigastric, cardial, etc.) before a general convulsive fit.

When the limbic zone is affected, there is fixative amnesia (memory impairment as Korsakov syndrome) and pseudo-reminiscences (false memories). Quite often emotional disorders (phobias, etc.). Disorders of central regulation of vegetative-visceral functions entail a violation of adaptation, adaptation to changing environmental conditions.

Callous body

In the callous body (corpus callosum) - a massive formation of white matter - pass commissural fibers that connect the paired parts of the hemispheres. In the anterior part of this large spike of the brain - in the knee (genu corporis callosi) - there are connections between the frontal lobes, in the middle section - in the trunk (corporus callosi) - between the parietal and temporal lobes, in the rear hotel - in thickening (splenium corporis callosi ) - between the occipital lobes.

Lesions of the corpus callosum are manifested by mental disorders. With foci in the anterior parts of the corpus callosum, these disorders carry features of the "frontal psyche" with confusion (disturbances in behavior, actions, criticism). Allocate frontal-callus syndrome (akinesia, amimia, aspontaneity, astasia-abasia, reflexes of oral automatism, reduction of criticism, memory impairment, grasping reflexes, apraxia, dementia). Dissociation of the connections between the parietal lobes leads to perverted perceptions of the "Tepa scheme" and the appearance of motor apraxia in the left upper limb; changes in the psyche of the temporal character are associated with disturbed perceptions of the external environment, with the loss of the correct orientation in it (syndrome "already seen", amnestic disorders, confabulation); foci in the posterior parts of the corpus callosum lead to complex kinds of visual agnosia.

Pseudobulbarnye symptoms (violent emotions, reflexes of oral automatism) are also common in defeats of the corpus callosum. At the same time, pyramidal and cerebellar disorders, as well as violations of cutaneous and deep sensitivity are absent, since their projection systems of innervation are not damaged. Of the central motor disorders, dysfunctions of the sphincters of the pelvic organs are more common.

One of the features of the human brain is the so-called functional specialization of the cerebral hemispheres. The left hemisphere is responsible for the logical, abstract, thinking, the right - for the concrete, imaginative. From which of the hemispheres is most morphologically developed and dominates in a person, depends on his personality, the features of perception (artistic or mental type of character).

When the right hemisphere is turned off, patients become verbose (even talkative), talkative, but their speech loses intonational expressiveness, it is monotonous, colorless, dull, acquires a nasal (nasal) shade. Such a violation of the intonational-voice component of speech is called dysprosium (prosody - melody). In addition, such a patient loses the ability to understand the meaning of the speech intonations of the interlocutor. Therefore, along with the preservation of the formal margin of speech (vocabulary and grammatical) and the increase in speech activity, the "right-hemisphere" person loses that imagery and concreteness of speech that is given to it by intonation-voice expressiveness. The perception of complex sounds is disturbed (auditory agnosia), a person ceases to recognize familiar melodies, can not sing them, finds difficulty in recognizing male and female voices (the image auditory perception is disrupted). The inferiority of figurative perception is also revealed in the visual sphere (does not notice the missing detail in unfinished drawings, etc.). The patient finds it difficult to perform tasks that require orientation in a visual, imaginative situation, where it is necessary to take into account specific features of the object. Thus, when the right hemisphere is turned off, those types of mental activity that underlie imaginative thinking suffer. At the same time, the types of mental activity that underlie abstract thinking are preserved or even intensified (alleviated). This state of mind is accompanied by a positive emotional tone (optimism, a tendency to joke, belief in recovery, etc.).

When the left hemisphere is affected, the speech capabilities of a person are sharply limited, the vocabulary is depleted, words that denote abstract concepts fall out of it, the patient does not remember the names of the objects, although they will recognize them. Speech activity is sharply reduced, but the intonation pattern of speech is preserved. Such a patient knows well the melodies of songs, can reproduce them. Thus, when the function of the left hemisphere is disturbed, the patient, along with the deterioration of verbal perception, retains all kinds of figurative perception. The ability to memorize words is disrupted, it is disoriented in place and time, but notices the details of the situation; a clear concrete orientation remains. Thus there is a negative emotional background (the patient's mood worsens, he is pessimistic, it is difficult to distract from sad thoughts and complaints, etc.).

[1], [2]