LECTURES ON NEUROPSYCHOLOGY: Lecture No. 10 5/5 (2)
Lecture No. 10 Neuropsychological syndromes of damage to the cortical parts of the cerebral hemispheres.
1 Projection zones of the cerebral cortex 2. Syndrome in neuropsychology 3. Cortical neuropsychological syndromes a. Syndromes of damage to the posterior parts of the PD cortex b. Syndromes of damage to the anterior parts of the cortex B P
- Brain zones There are three projection zones in the cerebral cortex. Primary projection zone - occupies the central part of the core of the brain analyzer. This is a collection of the most differentiated neurons in which the highest analysis and synthesis of information occurs, and clear and complex sensations arise there. Impulses approach these neurons along a specific impulse transmission pathway in the cerebral cortex (spinothalamic tract).
The secondary projection zone is located around the primary one, is part of the core of the brain section of the analyzer and receives impulses from the primary projection zone. Provides complex perception. When this area is damaged, a complex dysfunction occurs.
The tertiary projection zone, the association zone, consists of multimodal neurons scattered throughout the cerebral cortex. They receive impulses from the associative nuclei of the thalamus and converge impulses of different modalities. Provides connections between various analyzers and plays a role in the formation of conditioned reflexes.
Anatomical information In each hemisphere, the following surfaces are distinguished: 1. convex superolateral surface (facies superolateralis), adjacent to the inner surface of the bones of the cranial vault 2. lower surface (lat. facies inferior), the anterior and middle sections of which are located on the inner surface of the base of the skull, in areas of the anterior and middle cranial fossae, and the posterior ones - on the tentorium of the cerebellum 3. the medial surface (lat. facies medialis), directed towards the longitudinal fissure of the brain.
These three surfaces of each hemisphere, passing one into another, form three edges. The superior edge (lat. margo superior) separates the superolateral and medial surfaces. The inferolateral edge (lat. margo inferolateralis) separates the superolateral surface from the bottom. The inferomedial edge (lat. margo inferomedialis) is located between the lower and medial surfaces. In each hemisphere, the most prominent places are distinguished: in front - the frontal pole (lat. polus frontalis), in the back - occipital (lat. polus occipitalis), and on the side - temporal (lat. polus temporalis).
The hemisphere is divided into five lobes. Four of them are adjacent to the corresponding bones of the cranial vault: 1. frontal lobe (lat. lobus frontalis) 2. parietal lobe (lat. lobus parietalis) 3. occipital lobe (lat. lobus occipitalis) 4. temporal lobe (lat. lobus temporalis) 5. insular lobe (lat. lobus insularis) (island) (lat. insula) - located deep in the lateral fossa of the cerebrum (lat. fossa lateralis cerebri), separating the frontal lobe from the temporal lobe.
- Syndrome in neuropsychology In neuropsychology, the term “syndrome” has two meanings. The first concept is “neuropsychological syndrome” - a natural combination of HMF disorders that arise as a result of local brain damage and are based on a pathological change in one (or several) factors. The second meaning is a grossly expressed violation of any one function. In these cases, the expression “agnosia syndrome”, “semantic aphasia syndrome”, etc. is used. The study of neuropsychological syndromes is the main task of clinical neuropsychology (or syndromology) - the main direction of modern neuropsychology. Violations of the HMF can occur in different forms: 1. in the form of a gross dysfunction (or loss of function), 2. in the form of a pathological weakening (or strengthening) of the function 3. in the form of a decrease in the level of function performance.
By dysfunction, as a rule, we mean the collapse of its psychological structure. The classification of neuropsychological syndromes proposed by A. R. Luria is based on the topical principle, that is, on the principle of identifying the area of brain damage - the morphological basis of the neuropsychological factor.
In accordance with this principle, neuropsychological syndromes are divided: 1. into syndromes of damage to the cortical parts of the cerebral hemispheres and the “proximal subcortex”; 2. syndromes of damage to deep subcortical structures of the brain.
Cortical neuropsychological syndromes, in turn, are divided into lesion syndromes: ♦ lateral (convexital); ♦ basal; ♦ medial cortex of the cerebral hemispheres.
Subcortical neuropsychological syndromes are divided into syndromes involving: ♦ median nonspecific structures; ♦ median commissures (corpus callosum, etc.); ♦ structures located deep in the hemispheres (basal ganglia, etc.).
A special category consists of neuropsychological syndromes (cortical and subcortical) that arise from massive (tumor, traumatic, vascular) brain lesions involving both cortical and subcortical structures. In addition to the topical principle of classifying syndromes, the nosological principle is sometimes used. In these cases, syndromes are divided into “tumor”, “vascular”, “traumatic”, etc. Such a classification has predominantly clinical significance and emphasizes the features of neuropsychological syndromes associated with the nature of the disease. Sometimes syndromes are characterized depending on the patient’s age: “children’s” neuropsychological syndromes and “senile” neuropsychological syndromes.
HMF disorders included in the neuropsychological syndrome never occur in isolation from neurological disorders and other clinical symptoms of the disease. Therefore, neuropsychological (syndromic) analysis of mental processes disorders should always be combined with an analysis of the general clinical picture of the disease.
3 Cortical neuropsychological syndromes of the PD cortex Syndromes of damage to the cortical parts of the cerebral hemispheres (primarily the left hemisphere) have been studied in most detail in modern neuropsychology. Among cortical neuropsychological syndromes, the greatest attention has been paid to damage to the lateral (convexital) cortex.
Cortical neuropsychological syndromes occur when the secondary and tertiary fields of the cerebral cortex are damaged. Damage to the primary fields leads only to neurological symptoms - elementary disorders of sensory and motor functions. Cortical neuropsychological syndromes can generally be divided into two large categories: ♦ syndromes associated with damage to the posterior parts of the brain; ♦ syndromes associated with damage to the anterior parts of the cerebral hemispheres (left and right).
- Neuropsychological syndromes of damage to the posterior parts of the cerebral cortex.
The posterior sections of the cerebral cortex, located posterior to the Rolandic fissure, include the cortical nuclear zones of three main analyzer systems: 1. visual, 2. auditory, 3. cutaneous-kinesthetic.
They are divided into primary (17, 41, 3rd), secondary (18,19,42,22,1,2,5, 7th) and tertiary (37,39,40,21st) fields (total 52 fields pp. 55-60). Neuropsychological syndromes of damage to the posterior parts of the cerebral cortex have common features - they are based mainly on gnostic, mnestic and intellectual disorders associated with a violation of various modality-specific factors.
Modern neuropsychology describes the following neuropsychological syndromes that occur when the posterior convexital parts of the cerebral cortex are damaged.
- Syndromes of damage to the occipital and occipito-parietal cortex. These syndromes are based on disturbances in modality-specific visual and visuospatial factors associated with damage to the secondary cortical fields of the visual analyzer and adjacent parts of the parietal cortex.
Inability to combine complexes of visual stimuli into specific groups. Disturbances take on various forms and primarily manifest themselves in disorders of visual gnosis in the form of visual agnosia (objective, simultaneous, color, facial, alphabetic, optical-spatial), i.e., in disorders of visual perceptual activity.
Visual agnosia in its form depends on the side of the brain lesion - color, facial and optical-spatial agnosia are more often manifested when the right hemisphere of the brain is damaged. Letter and object agnosia - left (in right-handers).
According to another point of view, object agnosia in its expanded form is observed only with bilateral pathological lesions.
A special group of symptoms of damage to these parts of the brain consists of disturbances in visual memory and visual representations, which, in particular, manifest themselves in drawing defects (more often also in right-sided lesions). Lesions of the occipito-parietal parts of the cerebral cortex are often accompanied by symptoms of impaired visual (modality-specific) attention in the form of ignoring one part of the visual space.
An independent complex of neuropsychological symptoms in these lesions is associated with disturbances in optical-spatial analysis and synthesis. These disturbances manifest themselves in difficulties in orienting in external visual space (in one’s room, on the street, etc.), as well as in difficulties in perceiving spatial characteristics of objects and their images (maps, diagrams, watches, drawings, etc.). Visuospatial impairments can also manifest themselves in the motor sphere. In these cases, the spatial organization of motor acts suffers, as a result of which the praxis of the posture is disrupted and spatial (constructive) motor apraxia occurs.
There may be a combination of optical-spatial and motor-spatial disorders, which is called apraktoagnosia. Finally, an independent group of symptoms with damage to the occipito-parietal cortex (on the border with the temporal secondary fields) consists of disturbances of speech functions in the form of optical-mnestic aphasia. A feature of this form of speech disorders is disturbances in visual-figurative representations, as a result of which it becomes difficult to remember words denoting specific objects.
Thus, neuropsychological syndromes of damage to the occipital and occipital-parietal parts of the cerebral cortex include gnostic, mnestic, intellectual, motor and speech disorders caused by disturbances in modality-specific visual and visuospatial factors.
- Syndromes of damage to the TPO zone - the temporo-parietal-occipital sections of the cerebral cortex. These syndromes are based on violations of more complex - integrative ("associative") factors associated with the work of the tertiary fields of the cortex.
At the same time, when the SRW zone is damaged, the spatial analysis and synthesis itself is often disrupted. Damage to the SRW zone manifests itself in the following symptoms.
- difficulties in orientation in external visual space (especially in right-left spatial coordinates).
- motor-spatial disorders in the form of constructive apraxia, difficulties in writing letters (symptom of mirror copying).
The specificity of these syndromes consists in violations of complex intellectual functions associated with processes at the “quasi-spatial” level. These include, first of all, speech disorders of a special kind, known in neuropsychology under the name “so-called semantic aphasia.” In this case, impossible constructions include various logical-grammatical structures that arose relatively late in the history of language and express different types of relationships (spaces, sequences, etc.) using case endings or the arrangement of words in a sentence.
Complex semantic disorders with damage to the TPO area also include violations of symbolic “quasi-spatial” categories in the form of primary acalculia. They are expressed in the disintegration of understanding of the bit structure of numbers and, as a consequence, in the disruption of mental counting actions.
Intellectual disorders in this category of patients also manifest themselves at the speech level in the form of a lack of understanding of the corresponding logical and grammatical structures, which prevents the successful implementation of a number of verbal and logical intellectual operations. In their expanded form, neuropsychological syndromes of damage to the TPO zone occur with lesions in the left hemisphere of the brain (in right-handed people). With right-sided lesions in the TPO syndrome, there are no phenomena of semantic aphasia, but other problems include violations of counting and visual-figurative thinking. However, the problem of lateral differences in neuropsychological syndromes that arise when the TPO zone is damaged has not yet been sufficiently studied, as has the entire problem of the functions of the right hemisphere of the brain in general.
- Syndromes of damage to the parietal cortex of the brain. The parietal postcentral zones of the cerebral cortex occupy a large area, including a number of fields (secondary and tertiary). “Parietal” syndromes are associated with damage to the secondary cortical fields of the skin-kinesthetic analyzer, as well as tertiary parietal fields.
These syndromes are based on violations of modality-specific skin-kinesthetic factors. “Parietal” syndromes include various gnostic, mnestic, motor and speech disorders associated with the disintegration of tactile (or “tactile”) simultaneous syntheses. In neuropsychology, two main types of syndromes of damage to the parietal region of the brain are known: inferior parietal and superior parietal (independently).
- Syndromes of damage to the convexital cortex of the temporal region of the brain. The main factors causing the appearance of temporal cortex lesion syndromes are modality-specific - associated with the processing of sound information (speech and non-speech sounds).
Describing syndromes of damage to the temporal parts of the cortex of the left hemisphere, they distinguish: • a syndrome associated with damage to the T1 zone (“nuclear zone” of the auditory analyzer cortex), which is based on a phonemic hearing disorder, • a syndrome associated with damage to the T2 zone (areas located on the border temporal and parieto-occipital cortex), the basis of which is impairment of auditory-verbal memory. Damage to the temporal cortex of the right hemisphere leads to impairments in non-speech and musical hearing, as well as memory for non-speech sounds and musical memory. In these cases, the patient is unable to determine the meaning of various everyday sounds and noises (auditory agnosia) or does not recognize and cannot reproduce familiar melodies (amusia).
- Syndromes of damage to the mediobasal cortex of the temporal region of the brain. Damage to this cortex zone leads to disruption of modality-nonspecific factors.
The mediobasal regions of the temporal cortex are part of the limbic system of the brain, which is characterized by very complex functions. These include regulation of the level of wakefulness of the brain, emotional states, participation in the processes of memory, consciousness, etc. Three groups of symptoms included in these syndromes have been most studied.
The first group of symptoms is modality-nonspecific memory impairment (auditory-speech and other types). Defects in “general memory” manifest themselves in these patients as difficulties in directly retaining traces, i.e., in primary impairments of short-term memory.
The second group of symptoms is associated with disturbances in the emotional sphere. Damage to the temporal regions of the brain leads to distinct emotional disorders, which are classified in the psychiatric literature as affective paroxysms (in the form of attacks of fear, melancholy, horror), accompanied by violent vegetative reactions.
Such paroxysms usually precede general convulsive epileptic seizures. Long-term shifts in affective tone are also common. The nature of emotional disorders to a certain extent depends on the side of the lesion.
The third group of symptoms consists of symptoms of impaired consciousness. In some cases, these are drowsy states, confusion, and sometimes hallucinations; in others - difficulties in orientation in place, time, confabulation. With general epileptic seizures, a complete blackout of consciousness occurs, followed by amnesia for what happened.
Sensory areas of the cortex.
The area of the cortex where this type of sensitivity is projected is called the primary projection zone.
Human skin sensitivity, feelings of touch, pressure, cold and heat are projected into the postcentral gyrus. In its upper part there is a projection of the skin sensitivity of the legs and torso, below - the arms and completely below - the head.
The absolute size of the projection zones of individual areas of the skin is not the same. For example, the projection of the skin of the hands occupies a larger area in the cortex than the projection of the surface of the torso.
The magnitude of the cortical projection is proportional to the significance of a given receptive surface in behavior. Interestingly, the pig has a particularly large projection into the cortex of the snout.
Articular-muscular, proprioceptive sensitivity is projected into the postcentral and precentral gyri.
The visual cortex is located in the occipital lobe. When it is irritated, visual sensations arise - flashes of light; removing it leads to blindness. Removal of the visual zone on one half of the brain causes blindness in one half of each eye, since each optic nerve is divided at the base of the brain into two halves (forming an incomplete decussation), one of them goes to its half of the brain, and the other to the opposite.
If the outer surface of the occipital lobe is damaged, not the projection, but the associative visual zone, vision is preserved, but recognition disorder occurs (visual agnosia). The patient, being literate, cannot read what is written, recognizes a familiar person after he speaks. The ability to see is an innate ability, but the ability to recognize objects is developed throughout life. There are cases when a person blind from birth is restored to sight at an older age. For a long time he continues to navigate the world around him by touch. It takes a long time for him to learn to recognize objects using his vision.
The hearing function is provided by the precise lobes of the cerebral hemispheres. Their irritation is caused by simple auditory sensations.
Removal of both auditory zones causes deafness, and unilateral removal reduces hearing acuity. When areas of the auditory cortex are damaged, auditory agnosia can occur: a person hears, but ceases to understand the meaning of words. His native language becomes just as incomprehensible to him as a foreign language unfamiliar to him. The disease is called auditory agnosia.
The olfactory cortex is located at the base of the brain, in the region of the parahippocampal gyrus.
The projection of the taste analyzer appears to be located in the lower part of the postcentral gyrus, where the sensitivity of the oral cavity and tongue is projected.
https://www.medicinform.net/human/fisiology7_7.htm
Such zones are found in different lobes of the cortex. The zone of general sensitivity is located in the parietal lobe, the visual zone is in the occipital lobe, the auditory zone is in the temporal lobe, the gustatory zone is in the lower part of the parietal lobe, and the olfactory zone is in the two olfactory bulbs located under the cerebrum. The general sensitivity zone is located in the gyrus running along the Rolandic fissure, in the parietal lobe and receives signals from skin receptors. The entire human body - head down and toes up - is presented here in the form of areas (projections), the surface of which is proportional to the sensitivity of the corresponding parts of the body; Thus, the projection of the hand is much larger than the projections of the back or legs (Fig. A.25).
Rice. A.25. The size of the projections of sensory fibers in the comesthetic zone of the cortex is disproportionate to the size of those areas of the body from which these fibers extend (A). The same applies to the distribution of the centers of the motor zone, which are in charge of voluntary movements (B). By depicting the projections of various parts of the body in the cortex, this disproportion can be illustrated in the form of a sensory or motor homunculus.
Damage to all or any part of this area leads to a blockage of sensory signals from the corresponding areas of the body; as a result, tactile, temperature and pain sensations disappear here, although external stimuli continue to excite skin receptors and cause a flow of impulses in the nerve pathways coming from them. The association zone, located in the upper part of the parietal region, is gnostic and is responsible for the recognition and perception of stimuli that caused sensations at the level of the parietal gyrus. The zone of visual sensitivity is located in the occipital lobe along the calcarine sulcus, and the information transmitted by each retinal ganglion cell is very precisely projected to different points in it. The occipital zone of each hemisphere of the brain receives information from the opposite half of the visual field. Before entering the cerebrum, part of the fibers of both optic nerves intersect, forming the so-called optic chiasm (Fig. A.26). As a result of this crossing, the left visual lobe receives fibers from both eyes, carrying information about the right half of the visual field, and the right lobe - about the left half. Thus, as a result of the integration of nerve signals from both retinas, the brain recreates a three-dimensional image of an object, the images of which are slightly different on the right and left retinas.
Rice. A.26. Optic chiasm and visual pathways. Information about events in the right half of the visual field enters the left occipital lobe from the left side of each retina; information about the right half of the visual field is sent to the left occipital lobe from the right parts of both retinas. This redistribution of information from each eye occurs as a result of the crossing of part of the fibers of the optic nerve at the level of the optic chiasm.
Visual perception of objects, words and numbers is carried out in the associative zone located around the sensory zone. The auditory sensitivity zone is located in the temporal cortex. Each of the two temporal lobes receives information received by both ears. Therefore, even significant damage to the auditory zone cannot lead to deafness, unless, of course, it affects both cerebral hemispheres. The perception of sounds, including the interpretation of words and melodies, occurs in the association area located below the sensory area (see document 8.4). Taste and olfactory sensitivity are localized in areas located relatively close to each other. The gustatory zone is located at the base of the ascending gyrus and is responsible for deciphering nerve signals coming from the tongue. The area of olfactory sensitivity that dominates in most animals is reduced in humans to two olfactory bulbs, which are a continuation of the olfactory stripes at the base of the cerebrum.
https://www.gumer.info/bibliotek_Buks/Psihol/godfr/12.php
Nerve circuits
It is widely known that nerve cells are combined into networks, also called nerve circuits, that make up the white matter of the brain - conductors. Each neuron has approximately 7 thousand such circuits. Information is transmitted through conductors from cell to cell. The place of exchange is the connection point between the dendrite (short process) of one cell and the axon (long process) of another cell. Before connecting, the axon searches for “its own” dendrite, not just any one, and the moment of coincidence becomes marked by the formation of a synapse (contact).
The more synapses (Fig. 33), the more capacious the brain “computer” in terms of thinking and memory.
Rice. 33
. Neuron synapses
Despite the fact that the nerve impulse is electrical in nature, communication between neurons is ensured by chemical processes. For this purpose, the brain contains biochemical substances - neurotransmitters and neuromodulators. The moment the electrical signal reaches the synapse, the corresponding transmitters are released. They, like a vehicle, deliver a signal to another neuron. These neurotransmitters then break down. However, the process of transmitting nerve impulses does not end there, since the nerve cells located behind the synapse are activated and a postsynaptic potential arises. It generates an impulse that moves to another synapse, and the process described above is repeated thousands and thousands of times. This allows you to perceive and process a colossal amount of information.
Divisions of the cerebral cortex
The brain includes: the cerebral cortex, subcortical region and brain stem. Different parts of the brain are not the same in cellular (cytoarchitectonic), anatomical and morphological structure and, accordingly, in hierarchy.
The cerebral cortex is divided into the following lobes (Fig. 34):
• occipital (visual) lobe;
• parietal (tactile) lobe;
• temporal (auditory) lobe;
• frontal (control, regulatory) lobe.
Rice. 34
. Lobes of the cerebral cortex
The occipital, parietal and temporal lobes have the corresponding analyzer assignment. In neuropsychology it is usually referred to as modal specificity
. Thanks to them, various mental functions are carried out. The gustatory and olfactory regions are located on the medial (inner) surface of the temporal lobe. Their role in the implementation of cognitive functions in modern humans has ceased to be leading, that is, it is inferior in functional significance to the roles of the other lobes of the brain.
The frontal lobe has no modal specificity, but plays a dominant role in the implementation of higher nervous activity in humans. It occupies a vast area (more than half of the cortex) and is responsible for all brain processes.
Many publications on neurology and neurophysiology note that the most complex brain activity is ensured, in essence, by simple means. Some of the authors note that this simplicity reflects the universal law of “achieving great complexity through repeated transformations of simple elements
"(E. Goldberg). Thus, many words in a language are made up of a limited number of speech sounds and letters of the alphabet, countless musical melodies are made up of a small number of notes, the genetic codes of millions of people are provided by a finite number of genes, etc.
Chapter 2. Fields of the cerebral cortex
The concept of cortical fields and their functional hierarchy
The idea of differentiation of the cerebral cortex into three main types of fields, different in functional hierarchy: primary, secondary and tertiary, is extremely important for understanding how the human psyche is organized as a whole.
…
Primary fields
- these are the “cortical ends of the analyzers”, functioning naturally, innately. Primary fields have a clear assignment to a particular analyzer.
The primary fields are elementary, the secondary fields are more complex in structure and functioning, and, finally, the most complex in terms of these characteristics are the tertiary fields (Fig. 35).
Rice. 35
. Functional hierarchy of cortical fields
The primary fields of the auditory analyzers are located mainly on the inner surface of the temporal lobes of the brain, the kinesthetic (sensitive in general) - near the central (Rolland's) sulcus, in the parietal lobe. Primary sensory fields project to specific parts of the body: the upper parts receive sensory signals (sensations) from the lower extremities (legs), the middle parts process sensations from the upper extremities (arms), and the lower parts process sensations from the face, including parts of the speech apparatus (tongue). , lips, larynx, diaphragm). In addition, the lower parts of the parietal projection zone receive sensations from some internal organs.
Primary fields located in the brain area up to the central gyrus (anterior block of the brain) are tuned to the preparation and execution of motor acts. They are also projection, but in relation not to sensitive (kinesthetic - sensory), but to motor (motor) functions. In unique drawings made by the famous brain researcher W. G. Penfield
), it is clear that the significance of different parts of the body does not coincide with their size, but is determined by the role they play in the implementation of mental functions both in the perception of objects in the external world and in the reproduction of various actions (Fig. 36).
Rice. 36
. Functional representation of parts of the human body in the cerebral cortex
In the earliest ontogenesis, the nerve cells of the primary cerebral cortex function in isolation from each other, like separate worlds in space. Let's say a child recognizes his mother's voice, but does not recognize her face if she is silent. This separation of auditory and visual impressions at the level of sensations is especially often observed in relation to the father, whom infants see less often than their mother. The literature describes cases when a child, seeing his father's face bent over him, begins to cry loudly in fear until the adult speaks. Gradually, semantic, or rather informational connections (associations) are laid between the primary fields of the cerebral cortex. Thanks to them, the experience of sensations accumulates, that is, elementary knowledge about reality appears. For example, a child sees a rattle and knows that it will “rattle” if it is shaken.
The experience accumulated by primary fields interacting with each other serves as the basis, the starting point for the functional activation of secondary cortical fields
together
with tertiary fields
, which will be discussed later. Both are directly related to the implementation of the VPF.
The secondary fields of the auditory, tactile and visual cortex are distinguished, and in the anterior - premotor. Functionally, all three types of cortical fields are correlated vertically: the functions of the primary ones, the functions of the secondary ones are built on top of them, and the tertiary ones are built on top of the secondary ones. However, anatomically they are not located above each other, but horizontally: primary fields (I) are close to the core of the zones, secondary fields (II) are in its middle sections, and tertiary fields (III) are on the periphery (Fig. 37).
Rice. 37
. Scheme of the functional hierarchy of fields of the cerebral cortex
Primary fields form the core of a particular analyzer zone. Secondary fields are shifted to the periphery of the zone, and tertiary fields are even further away. The sizes of fields different in hierarchy are also proportional to the proximity to the nucleus: primary ones occupy a small area, secondary ones occupy a medium area, and tertiary ones occupy the largest area. As a result, the fields overlap each other, forming so-called “overlap” zones. These include, for example, the most important zone of the TPO within the framework of higher human activity - the temporo-parietal-occipital zone: T
emporalis -
Parietalis
-
Occipitalis
. The first three letters of these Latin designations make up the abbreviation TPO.
Primary fields are homogeneous in cellular composition. Olfactory fields contain only olfactory nerve cells, auditory fields - only auditory ones, etc. Despite the universality of the physiological and biochemical mechanisms that ensure the functioning of the brain, its different parts function differently, that is, they have different functional specializations
, representing different modalities.
Secondary fields are less uniform. The cells of the predominant modality are interspersed with cells of other modalities. Therefore, secondary fields, although modality-specific, like primary ones, are less “rigid” in this regard. Tertiary fields, being zones of overlap, contain not only cells of different analyzers, but also their entire zones. Thanks to their functioning, the most complex types of human activity are realized, and in particular speech.
The secondary and tertiary fields of the cortex are distinguished by differences in functioning depending on lateralization, that is, location in one or the other hemisphere of the brain. For example, both temporal lobes, belonging to the same modality, namely the auditory modality, perform different “work”. The temporal lobe of the right hemisphere, for example, is responsible for processing non-speech noise (produced by nature, including the sounds of animals, objects, including musical instruments and music itself, which can be considered the highest form of non-speech noise). The temporal lobe of the left hemisphere processes speech signals. In addition to the differences in the specialization of the temporal lobes of the brain, which belong to different hemispheres, one can also see here the principle of “protection” of the most important functions, so characteristic of nature, and even more so, such an important and necessary for any person as speech.
Lecture 4 Cortical centers of the cerebral cortex.
The concept of cortical center was proposed by I.P. Pavlov. Cortical center
has no clear boundaries and consists of nuclear and scattered parts. Cortical centers are located in the lobes of the brain.
I. Frontal lobe of the brain.
1. Motor zone
located in the precentral gyrus.
In the upper third there are neurons that innervate the leg, in the middle - the arm, in the lower third - the face, tongue, larynx and pharynx. Irritation of this area with a weak electric current leads to contraction of a specific muscle group. When the motor area of the brain is impaired, paresis
(weakening of movements) and
paralysis
(complete absence of movements) occur.
2. Center of combined head and eye rotation
located in the middle frontal gyrus. It is a bilateral center and performs a combined rotation of the head and eyes in the opposite direction. If the center in the right hemisphere is damaged, the head and eyes look to the right side, i.e. towards the damage. A patient with such damage cannot turn his head and eyes in the direction opposite to the damaged part.
3. Motor speech center
(
Broca's center
) - located in the posterior lower part of the third frontal gyrus of the left hemisphere (in right-handed people). If damaged, motor speech (the ability to speak) is impaired.
4. Writing Center
(
graphic center
) is located in the posterior parts of the middle frontal gyrus.
If damaged, the ability to write is impaired ( agraphia
).
II. Parietal lobe.
1. Center for General Sensitivities
– located in the parietal lobe behind the central sulcus (Roland’s sulcus). It is a two-sided center. The sensitive centers of the legs are located in the upper section, the arms in the middle section, and the heads in the lower section. If the center is damaged, sensory disturbances in the corresponding organs occur.
2. Center for the perception of complex types of sensitivity
– bilateral center located in the superior parietal lobule. Responsible for the perception of weight, two-dimensionality, etc.
3. Body diagram center
– located inside the parietal sulcus. Lesions of the center lead to violations of the correct ideas about the size, shape, and location of parts of one’s body.
4. Praxia Center
– located above the marginal gyrus of both hemispheres.
Ensures the execution of complex, targeted movements in a specific sequence. When the center is damaged, disturbances in purposeful movements and actions occur while its constituent elementary movements ( apraxia
) are preserved. There are three types of apraxia:
- ideatorial
(apraxia of design) – a disorder in the sequence of movements when performing a task;
- motor
(apraxia of execution) - a disorder of acting on orders or imitation;
- constructive
– the impossibility of constructing a whole movement from its individual parts.
5. Stereognosia Center
– located behind the middle part of the postcentral gyrus. If damaged, the ability to recognize objects by touch is impaired.
6. Lexicon Center
– located in the angular gyrus of the left hemisphere in right-handed people.
Responsible for the ability to recognize printed characters and read. alexia
occurs - a reading disorder.
7. Account center
(
calculia
) - located above the angular gyrus.
When the center is damaged, the ability to count is impaired - acalculia
.
8. Center for Semantic Aphasia
– located in the convergence area of the parietal, occipital and temporal lobes. If damaged, the ability to understand complex verbal, grammatical, temporal, and semantic structures is impaired.
III. Temporal lobe.
1. Sensory Speech Center
(
Wernicke's center
) - located in the posterior part of the superior temporal gyrus of the left hemisphere in right-handed people.
Responsible for understanding spoken language. Damage to the center leads to sensory aphasia
- a violation of the understanding of oral speech.
2. Amnestic Aphasia Center.
If damaged, the ability to name objects whose purpose is well known to the patient is impaired.
3. Hearing Center
– bilateral center, located in the superior temporal gyrus and partially in the transverse temporal gyrus. If damaged, hearing is impaired in both ears, but to a greater extent in the opposite ear, i.e. If there is damage in the left hemisphere, the hearing of the right ear suffers more.
4. Center of taste and smell
– located in the hippocampus region. If damaged, the ability to perceive taste and smell is impaired.
IV. Occipital lobe.
1. Center of vision
– located in the area of the calcarine sulcus and sphenoid gyrus. When damaged, visual impairment and loss of visual fields occur.
2. Center for Visual Gnosia
– located on the superolateral surface of the occipital lobe. If damaged, the ability to recognize objects is impaired.
Lecture 6 Cerebellum
Cerebellum
is a department of the central nervous system. Takes part in coordination of movements, regulation of balance, accuracy, proportionality and correctness of movements, regulates muscle tone, and is the most important center of the autonomic (?) nervous system.
Located in the posterior cranial fossa behind the brain stem. Consists of the cerebellar hemispheres
and
the cerebellar vermis
. The cerebellar vermis is responsible for static coordination, the cerebellar hemispheres are responsible for dynamic coordination of movements. Somatotopically, the muscles of the trunk are represented in the cerebellar vermis, and the muscles of the limbs are represented in the hemispheres.
The surface of the cerebellum is covered by a layer of gray matter that makes up the cerebellar cortex. The cerebellar cortex is covered with thin grooves and convolutions. There are several lobes of the cerebellum.
White matter forms the cerebellar peduncles
, in which the conducting paths are located.
The cerebellar peduncles are divided into inferior
,
middle
and
superior
. The lower legs are connected to the medulla oblongata, the middle ones to the pons, and the upper legs to the midbrain.
The white matter of the cerebellum contains nuclei
gray matter:
1. Tent core;
2. Globular nucleus;
3. Dentate nucleus;
4. Corky nucleus.
Text of the book “Human Physiology. General. Sports. Age"
3.8.2. Functional significance of various cortical fields According to the structural features and functional significance of individual cortical areas, the entire cortex is divided into three main groups of fields - primary, secondary and tertiary
(Fig. 7).
Primary fields are associated with sensory organs and organs of movement on the periphery. They provide sensations.
These include, for example, the field of pain and muscle-articular sensitivity in the posterior central gyrus of the cortex, the visual field in the occipital region, the auditory field in the temporal region and the motor field in the anterior central gyrus.
The primary fields contain highly specialized determinant cells, or detectors, that selectively respond only to certain stimuli. For example, in the visual cortex there are detector neurons that are excited only when the light is turned on or off, sensitive only to a certain intensity, to specific intervals of light exposure, to a certain wavelength, etc. When the primary fields of the cortex are destroyed, the so-called cortical blindness, cortical deafness, etc.
Fig. 7. Primary, secondary and tertiary fields of the cerebral cortex.
A: large points - primary fields, medium - secondary fields, small - tertiary fields;
B: primary (projection) fields of the cerebral cortex
Secondary fields are located next to the primary ones. In them, comprehension and recognition of sound, light and other signals occur, and complex forms of generalized perception arise.
When secondary fields are damaged, the ability to see objects and hear sounds is retained, but the person does not recognize them and does not remember the meaning.
Tertiary fields are developed almost only in humans.
These are associative areas of the cortex, providing higher forms of analysis and synthesis and forming purposeful human behavioral activity.
Tertiary fields are located: in the posterior half of the cortex - between the parietal, occipital and temporal regions;
in the anterior half - in the anterior parts of the frontal areas. Their role is especially great in organizing the coordinated work of both hemispheres.
Tertiary fields mature in humans later than other cortical fields and degrade earlier than others during aging.
The function of the posterior tertiary fields (mainly the inferior parietal areas of the cortex) is to receive, process and store information.
They form an idea of
the body diagram and the spatial diagram,
providing spatial orientation of movements.
The anterior tertiary fields (frontal areas)
perform general regulation of complex forms of human behavior, forming
intentions and plans, programs of voluntary movements and control over their implementation.
The development of tertiary fields in humans is associated with the function of speech.
Thinking (inner speech) is possible only with the joint activity of various sensory systems, the integration of information from which occurs in tertiary fields. With congenital underdevelopment of the tertiary fields, a person is not able to master speech (pronounces only meaningless sounds) and even the simplest motor skills (cannot dress, use tools, etc.). 3.8.3.
Paired activity and hemispheric dominance Information processing is carried out as a result of paired activity of both hemispheres
brain.
However, as a rule, one of the hemispheres is leading - dominant.
In most people with a dominant right hand (right-handed people),
the left hemisphere is dominant, and the right hemisphere is subordinate (subdominant).
Left hemisphere versus right
has a finer neural structure, a greater richness of neuronal connections, a more concentrated representation of functions and better blood supply conditions. In the left dominant hemisphere there is a motor speech center (Broca's center), which provides speech activity, and a sensory speech center, which carries out the understanding of words. The left hemisphere is specialized in fine sensorimotor control of hand movements.
In humans, there are three forms of functional asymmetry: motor, sensory and mental.
Typically, a person has a dominant arm, leg, eye and ear.
However, the problem of functional asymmetry is quite complex. For example, a right-handed person may have a dominant left eye or left ear, the signals from which are dominant. Moreover, in each hemisphere the functions of not only the opposite, but also the same side of the body can be represented. As a result of this, it is possible to replace one hemisphere with another in case of damage, and also creates a structural basis for the variable dominance of the hemispheres in controlling movements.
Mental asymmetry manifests itself in the form of a certain specialization of the hemispheres. For the left hemisphere
characterized by analytical processes, sequential processing of information, including with the help of speech, abstract thinking, assessment of temporary relationships, anticipation of future events, successful solution of verbal and logical problems.
In the right hemisphere,
information is processed holistically, synthetically (without breaking down into details), taking into account past experience and without the participation of speech; substantive thinking predominates.
These features make it possible to associate the perception of spatial features and the solution of visuospatial problems with the right hemisphere. The functions of the right hemisphere are associated with the past time, and the left hemisphere with the future. 3.8.4.
Electrical activity of the cerebral cortex Changes in the functional state of the cortex are reflected in the recording of its electrical activity - an electroencephalogram (EEG). Modern electroencephalographs amplify brain potentials by 2–3 million times and make it possible to study EEG from many points of the cortex simultaneously, i.e., to study system processes. EEG registration is carried out in the form of an ink recording on paper, as well as in the form of a complete picture on a diagram of the surface of the brain, i.e., a brain map (mapping method) on the monitor screen of modern computer systems (Fig. 8).
Rice. 8. Brain Mapping:
multichannel recording of a human electroencephalogram (EEG) on a monitor screen and reflection of excited (light zones) and inhibited (dark zones) areas of the cortex
Rice. 9. EEG of the occipital (a-e) and motor (f-h) areas of the human cerebral cortex under various conditions and during muscle work:
a – active state, eyes open (beta rhythm); b – rest, eyes closed (alpha rhythm); c – drowsiness (theta rhythm); d – falling asleep (slow waves); d – deep sleep (delta rhythm); f – unusual or hard work – asynchronous frequent activity (the phenomenon of desynchronization); g – cyclic work – slow potentials at the pace of movements (“marked rhythms” of EEG); h – execution of a mastered movement – appearance of alpha rhythm
There are certain frequency ranges,
called EEG rhythms (Fig. 9): in a state of relative rest, the alpha rhythm is most often recorded (8-13 oscillations per 1 s); in a state of active attention - beta rhythm (14 oscillations per 1 s and higher); when falling asleep, in some emotional states – theta rhythm (4–7 oscillations per 1 s); during deep sleep, loss of consciousness, anesthesia - delta rhythm (1-3 fluctuations per 1 s).
The EEG reflects the peculiarities of the interaction of cortical neurons during mental and physical work
(Livanov M.N., 1972). The lack of well-established coordination when performing unusual or difficult work leads to the so-called EEG desynchronization - rapid asynchronous activity. As a motor skill is formed, EEG synchronization phenomena arise in the EEG—increasing interconnectedness (synchrony and in-phase) of the electrical activity of different cortical areas involved in movement control. During cyclic work, slow potentials appear at the pace of the performed, imaginary or upcoming movement - “marked rhythms” (Sologub E.B., 1973).
In addition to background activity, the EEG identifies individual potentials associated with certain events:
evoked potentials that arise in response to external stimuli (auditory, visual, etc.); potentials reflecting brain processes during the preparation, implementation and completion of individual motor acts - this is the “wave of anticipation”, or a conditioned negative wave (Walter G, 1966), premotor, motor and final potentials, etc. In addition, various upper slow ones are recorded fluctuations lasting from several seconds to tens of minutes (in particular, the so-called “omega potentials”, etc.), which reflect the biochemical processes of regulation of functions and mental activity.
Higher nervous activity
Developing the ideas of I.M. Sechenov on the reflex basis of behavioral activity of the whole organism, I.P. Pavlov came to the idea that in changing environmental conditions it is not enough to have standard reflex reactions, but the development of new reflexes is required,
adequate to the new conditions of existence.
He first spoke about conditioned reflexes in his famous Madrid speech in 1903. 4.1.
Conditions for the formation and types of conditioned reflexes Conditioned reflexes differ from unconditioned reflexes in many ways (Table 1).
Conditioned reflexes in mammals and humans are carried out by the cerebral cortex (the thalamic part of the diencephalon and, in some cases, the subcortical nuclei also take part in this).
I.P. Pavlov developed an objective method
the study of acquired or conditioned reflexes, which was based on
the isolation
of the examined organism from extraneous stimuli and on
the accurate recording of the signal and the response to it.
Table 1
Differences between conditioned and unconditioned reflexes
The studies were conducted on dogs in soundproof chambers (“towers of silence”), where dosed irritations from light, sound, mechanical irritations of the skin, etc. were applied. The response was the release of saliva, which was diverted from one of the salivary ducts located on the outer surface of the cheek (salivary gland fistula technique).
In the process of developing acquired reflexes, the following conditions must be met:
• combination of any indifferent stimulus with any significant unconditioned stimulus
(for example, food) - the technique of unconditional reinforcement;
• indifferent irritation must precede unconditional irritation,
to acquire signal value;
• nerve centers,
to which stimulation is addressed
must be in a state of optimal arousal.
For example, after a preliminary isolated action of a light signal, the dog was given reinforcement - meat powder and salivation was recorded. After a series of combinations of these signals, just turning on the light caused the release of saliva, i.e., a new reflex, a biological meaning,
which was to
prepare the body for
food intake.
Education mechanism
The conditioned reflex consisted
in the formation of a new reflex arc,
in which a new afferent beginning of the reflex arc, coming from the visual pathways, was added to the efferent part of the unconditioned reflex. A new connection was formed between the centers of these initial reflexes, which I.P. Pavlov called it a temporary connection, since if the food supply was stopped after the light signal, the salivary conditioned reflex disappeared.
During the development of the conditioned reflex, certain phases
this process:
1) generalization
(generalized perception of a signal, when a conditioned reaction was observed to any similar signal), the basis of which was the processes
of irradiation of excitation
in the cerebral cortex;
2) excitation concentrations
(reaction only to a specific signal), which appeared due to the developed
conditioned inhibition
to extraneous non-reinforced signals;
3) stabilization
(strengthening the conditioned reflex).
In further studies, conditioned reflexes were developed under a variety of experimental conditions (including conditions of free behavior) in various animals, birds, fish, turtles, even amoebas. The study of the biopotentials of the cerebral cortex showed that the condition for the formation of a temporary connection between the studied cortical centers is the spatial synchronization of their electrical activity.
There are several types of conditioned reflexes:
1) natural –
to signals characterizing unconditioned stimuli (for example, the smell of meat for the salivary reflex), and
artificial -
to extraneous signals (for example, the smell of mint);
2) cash and trace
on the conditioned signal immediately preceding unconditional reinforcement and on its subsequent influence;
3) positive
(with active manifestation of the response)
and negative
(with its inhibition);
4) conditioned reflexes for time -
when conditioned signals are given rhythmically, the response appears at a given interval even in the absence of the next signal;
5) conditioned reflexes of the first order –
to one previous conditioned stimulus - and
higher orders,
when unconditional reinforcement is preceded by a combination of two sequentially applied signals (light + sound) - a conditioned reflex of the second order, three signals (light + sound + tangent) - a conditioned reflex of the third order, etc.
Dogs develop mainly third-order reflexes, monkeys develop fourth-order reflexes, infants develop 5–6-order reflexes, and adults develop twentieth-order or more. The acquisition of speech by a person is the formation of a huge chain of conditioned unconditioned reflexes that do not require special reinforcement.
When forming new motor skills, special reflexes arise, which, unlike sensory reflexes or reflexes of the first kind
(in which the new part of the reflex arc was the afferent part) have a new part of the reflex arc in the efferent section (new executive apparatus - muscles).
These are the so-called instrumental, or operant, reflexes - reflexes of the second kind
(Konorsky Yu.M., 1970).
4.2.
External and internal inhibition of conditioned reflexes According to its origin, inhibition of conditioned reflexes can be unconditioned (innate) and conditioned (developed during life).
Unconditioned inhibition includes
protective, or transcendental, inhibition
that occurs with excessively strong or prolonged stimulation, and
external inhibition
of conditioned reflexes by stimuli foreign to the centers of the conditioned reflex (for example, a violation of a fragile motor skill in an athlete under unusual competition conditions).
Conditioned inhibition is developed in the absence of reinforcement of the conditioned signal. There are several types of conditioned inhibition: extinction, differentiation and delay.
Extinction develops when a conditioned signal is repeated without reinforcement. For example, having a strong salivary conditioned reflex in a dog to a flash of light and then using light without reinforcement, you can consistently obtain the following conditioned responses - 10, 8, 6, 4, 5, 2, 0, 0, 0 drops of saliva.
Differential inhibition is produced by reinforcement of one conditioned signal (for example, a sound with a frequency of 500 Hz) and the absence of reinforcement of similar signals (sound of 1000, 200 and 100 Hz), to which a conditioned response was initially obtained (during the period of generalization of the conditioned reflex). This type of inhibition, in particular, allows the athlete to differentiate contractions of unnecessary muscles when developing a motor skill, i.e., it has important coordination significance. The process of human upbringing is accompanied by constant differentiation of behavioral reactions reinforced and condemned by society (what is “good” and what is “bad”).
Delayed inhibition is formed when reinforcement is delayed from the conditioned signal for a certain period of time.
In this case, immediately after the conditioned signal the reaction is absent (inhibited), but before the moment of reinforcement it is detected. 4.3.
Dynamic stereotype In life, one usually encounters not individual conditioned reflexes, but complex complexes of them, in which they are combined with unconditioned reflexes (motor, cardiovascular, respiratory, etc.). A system of conditioned and unconditioned reflexes
I.P.
Pavlov called it a dynamic stereotype. It is developed by repeating the same order of stimuli (situations)
and is accordingly expressed in a chain of fixed responses, i.e.,
a stereotype.
But a change in external conditions can cause a restructuring of this system or its destruction, which is indicated by the term
“dynamic”.
For example, a dog has developed a dynamic stereotype for a certain order of 6 stimuli, and there are fixed conditional values of salivation on them, specific for each signal: 1) light - 12 drops; 2) sound – 20 drops; 3) metronome 120 beats/s – 10 drops; 4) metronome 60 beats/s (non-reinforced stimulus) – 0 drops; 5) light – 12 drops; 6) sound -20 drops. If we now give the same signal, then the response chain of reactions will remain the same: 1) light - 12 drops; 2) light -20 drops; 3) light – 10 drops; 4) light – 0 drops; 5) light -12 drops; 6) light – 20 drops. However, the isolated inclusion of light stimulation retains the usual response - 12 drops.
Consequently, in the dog’s cerebral cortex a chain of sequentially excited or inhibited nerve centers is formed,
in which the activity of each automatically causes the activation of the next.
A similar stereotype arises in an athlete when developing a motor skill, especially when performing standard movements. Such a stereotype associated with a chain of motor acts, A.N. Krestovnikov called it a “motor dynamic stereotype.”
It is more easily formed when performing cyclic exercises than acyclic ones.
4.4.
Types of higher nervous activity, the first and second signaling system. A severe flood that occurred in Leningrad in 1924 threatened to flood the cages with experimental dogs, which experienced severe stress. The next day it was discovered that some of them had lost their well-developed conditioned reflexes, but others had retained their reflexes. This prompted I.P. Pavlov's ideas about different types of nervous system
in animals.
As the main properties of the nervous system I.P.
Pavlov considered the strength of excitation and inhibition, their balance and mobility. Taking these properties into account, he identified the following
four types of higher nervous activity
(HNA), which turned out to be similar to the four temperaments identified by Hippocrates in the 5th century BC. e.
1. Strong unbalanced type (choleric).
It is characterized by a strong process of excitation and a weaker process of inhibition, therefore it is easily excited and has difficulty inhibiting its reactions.
2. The type is strong, balanced and highly mobile (sanguine).
It is distinguished by strong balanced and highly mobile processes of excitation and inhibition. Easily switches from one form of activity to another, quickly adapts to a new situation.
3. The type is strong, balanced, inert (phlegmatic).
It has strong and balanced processes of excitation and inhibition, but is sedentary - slowly switching from excitation to inhibition and back. It is difficult to move from one type of activity to another, but is resilient during long-term work. Slowly but firmly adapts to unusual environmental conditions.
4. Weak type (melancholic).
It is characterized by weak processes of excitation and inhibition, with some predominance of the inhibitory process, is poorly adaptive, and is susceptible to neuroses. But it is highly sensitive to mild irritations and can easily differentiate them.
The described types are found in animals and humans. They represent only extreme manifestations of the characteristics of the nervous system, between which there may be a significant number of transitional types.
In addition, I.P. Pavlov identified specifically human types of GNI,
associated with the presence in humans of a special second signaling system -
words visible, audible, written, pronounced,
in contrast to the first signaling system, common to humans and animals -
direct stimuli to the external or internal environment of the body.
The second signaling system has enormously expanded the adaptive capabilities of humans.
Its properties are: generalization of the signals
of the first and second signal systems, the emergence
of abstractions
(complex complex concepts - courage, rage, kindness, etc.), the possibility of
transferring the accumulated experience
of previous generations to subsequent ones (the emergence of science, culture, etc.). The second signal system thus formed the basis of written and oral speech, the appearance of mathematical and musical symbols, and abstract human thinking. Its activity is associated with the functions of the tertiary fields of the cerebral cortex, predominantly the left hemisphere in right-handed people, where the speech centers are located.
Due to the different ratio in people of reactions associated with the predominance of the first or second signaling system, I.P. Pavlov distinguished specifically human types
nervous system:
“mental” – with
a predominance of the second signaling system;
“artistic” – with
a predominance of the first signal system.
Among adults, the number of people with a predominance of the second signaling system is about half of the population. About 25% are people with a predominance of the first signaling system and about 25% are people who have a balance of both systems. According to these types, two main forms of human intelligence are currently distinguished : non-verbal intelligence,
reflecting the individual’s natural abilities to manipulate immediate (especially visual-spatial) stimuli, and
verbal intelligence,
reflecting the ability to manipulate verbal material, which determines the nature of behavioral reactions, including including in sports.
