Cognitive functions are localized in the cerebral cortex. Localization of functions in the cortex. Topical diagnosis of cortical lesions
The cortex of the cerebral hemispheres is formed by gray matter, which lies along the periphery (on the surface) of the hemispheres. The thickness of the cortex in different parts of the hemispheres ranges from 1.3 to 5 mm. The number of neurons in the six-layer cortex in humans reaches 10 - 14 billion. Each of them is connected via synapses with thousands of other neurons. They are located in correctly oriented "columns".
Various receptors perceive the energy of irritation and transmit it in the form of a nerve impulse to the cerebral cortex, where all stimuli that come from the external and internal environment are analyzed. In the cerebral cortex there are centers (cortical ends of the analyzers that do not have strictly delineated boundaries) that regulate the performance of certain functions (Fig. 1).
Fig. 1. Cortical Analyzer Centers
1 - the core of the motor analyzer; 2 - frontal lobe; 3 - core of the taste analyzer; 4 - motor center of speech (Broca); 5 - the core of the auditory analyzer; 6 - temporal center of speech (Wernicke); 7 - temporal lobe; 8 - occipital lobe; 9 - the core of the visual analyzer; 10 - parietal lobe; 11 - the core of the sensitive analyzer; 12 - middle slit.
In the cortex of the postcentral gyrus and the superior parietal lobule, the nuclei of the cortical analyzer of sensitivity (temperature, pain, tactile, muscle and tendon sensation) of the opposite half of the body lie. Moreover, at the top are the projections of the lower extremities and lower parts of the body, and at the bottom are the receptor fields of the upper body and head. The proportions of the body are very distorted (Fig. 2), because the representation in the cortex of the hands, tongue, face and lips accounts for a much larger area than the body and legs, which corresponds to their physiological significance.
Rice. 2. Sensitive homunculus
1 - fades superolateralis hemispherii (gyrus post-centralis); 2 - lobus temporalis; 3 - sul. lateralis; 4 - ventriculus lateralis; 5 - fissura longitudinalis cerebri.
Shown are the projections of parts of the human body on the area of the cortical end of the general sensitivity analyzer, localized in the cortex of the postcentral gyrus; frontal section of the hemisphere (diagram).
Fig. 3. Motor homunculus
1 - facies superolateralis hemispherii (gyrus precent-ralis); 2 - lobus temporalis; 3 - sulcus lateralis; 4 - ventriculus lateralis; 5 - fissura longitudinalis cerebri.
The projections of parts of the human body on the area of the cortical end of the motor analyzer, localized in the cortex of the precentral gyrus of the large brain are shown; frontal section of the hemisphere (diagram).
The nucleus of the motor analyzer is located mainly in the pre-central gyrus ("motor area of the cortex"), and here the proportions of parts of the human body, as in the sensitive area, are highly distorted (Fig. 3). The dimensions of the projection zones of various parts of the body do not depend on their actual size, but on their functional significance. Thus, the zones of the hand in the cerebral cortex are much larger than the zones of the trunk and lower extremities taken together. The motor regions of each of the hemispheres, which are highly specialized in humans, are associated with the skeletal muscles of the opposite side of the body. If the muscles of the limbs are isolated in isolation with one of the hemispheres, then the muscles of the trunk, larynx and pharynx - with the motor areas of both hemispheres. From the motor cortex, nerve impulses are directed to the neurons of the spinal cord, and from them to the skeletal muscles.
The core of the auditory analyzer is located in the temporal lobe cortex. To each of the hemispheres, there are pathways from the receptors of the hearing organ on both the left and right sides.
The nucleus of the visual analyzer is located on the medial surface of the occipital lobe. Moreover, the nucleus of the right hemisphere is connected by pathways with the lateral (temporal) half of the retina of the right eye and the medial (nasal) half of the retina of the left eye; left - with the lateral half of the retina of the left and medial half of the retina of the right eye.
Due to the close proximity of the nuclei of the olfactory (limbic system, hook) and gustatory analyzers (the lowest parts of the postcentral cortex), the senses of smell and taste are closely related. The nuclei of the gustatory and olfactory analyzers of both hemispheres are connected by pathways with receptors on both the left and right sides.
The described cortical ends of the analyzers carry out the analysis and synthesis of signals coming from the external and internal environment of the body, constituting the first signaling system of reality (I.P. Pavlov). Unlike the first, the second signaling system is present only in humans and is closely related to articulate speech.
The cortical centers account for only a small area of the cerebral cortex; areas that do not directly perform sensory and motor functions predominate. These areas are called associative areas. They provide connections between different centers, are involved in the perception and processing of signals, combining the information received with emotions and information stored in the memory. Modern research suggests that higher-order sensitive centers are located in the associative cortex (V. Mountcastle, 1974).
Human speech and thinking are carried out with the participation of the entire cerebral cortex. At the same time, in the cortex of the human cerebral hemispheres there are zones that are the centers of a number of special functions associated with speech. The motor analyzers of speech and writing are located in the areas of the frontal lobe cortex near the nucleus of the motor analyzer. The centers of visual and auditory speech perception are located near the nuclei of the analyzers of vision and hearing. At the same time, speech analyzers in "right-handers" are localized only in the left hemisphere, and in "left-handers" - in most cases, also on the left. However, they can be located on the right or in both hemispheres (W. Penfield, L. Roberts, 1959; S. Dimond, D. Bleizard, 1977). Apparently, the frontal lobes are the morphological basis of the mental functions of a person and his mind. During wakefulness, a higher activity of neurons in the frontal lobes is observed. Certain areas of the frontal lobes (the so-called prefrontal cortex) are associated with numerous connections with various parts of the limbic nervous system, which allows them to be considered cortical parts of the limbic system. The prefrontal cortex plays the most important role in emotion.
In 1982, R. Sperry was awarded the Nobel Prize "for his discoveries concerning the functional specialization of the cerebral hemispheres." Sperry's research has shown that the left cerebral cortex is responsible for verbal (Latin verbalis - verbal) operations and speech. The left hemisphere is responsible for understanding speech and performing movements and gestures associated with language; for mathematical calculations, abstract thinking, interpretation of symbolic concepts. The cortex of the right hemisphere controls the performance of non-verbal functions, it controls the interpretation of visual images, spatial relationships. The cortex of the right hemisphere makes it possible to recognize objects, but does not allow expressing it in words. In addition, the right hemisphere recognizes sound patterns and perceives music. Both hemispheres are responsible for the consciousness and self-awareness of a person, his social functions. R. Sperry writes: "Each hemisphere ... has, as it were, its own separate thinking." Anatomical examination of the brain revealed interhemispheric differences. At the same time, it should be emphasized that both hemispheres of a healthy brain work together to form a single brain.
Localization of functions in the cerebral cortex
General characteristics. In certain areas of the cerebral cortex, mainly neurons are concentrated that perceive one type of stimulus: the occipital region - light, the temporal lobe - sound, etc. However, after removing the classic projection zones (auditory, visual), conditioned reflexes to the corresponding stimuli are partially preserved. According to the theory of IP Pavlov in the cerebral cortex there is a "nucleus" of the analyzer (cortical end) and "scattered" neurons throughout the cortex. The modern concept of localization of functions is based on the principle of multifunctionality (but not equivalence) of cortical fields. The property of multifunctionality allows one or another cortical structure to be included in the provision of various forms of activity, while realizing the main, genetically inherent function of it (OS Adrianov). The degree of multifunctionality of various cortical structures is not the same. It is higher in the fields of the associative cortex. Multifunctionality is based on the multichannel flow of afferent excitation into the cerebral cortex, overlapping of afferent excitations, especially at the thalamic and cortical levels, the modulating effect of various structures, for example, nonspecific thalamic nuclei, basal ganglia on cortical functions, the interaction of cortical-subcortical and intercortical pathways of excitation. With the help of microelectrode technology, it was possible to register in various areas of the cerebral cortex the activity of specific neurons responding to stimuli of only one type of stimulus (only to light, only to sound, etc.), i.e., there is multiple representation of functions in the cerebral cortex ...
At present, the division of the cortex into sensory, motor and associative (nonspecific) zones (areas) is accepted.
Sensory areas of the cortex. Sensory information enters the projection cortex, cortical sections of the analyzers (I.P. Pavlov). These zones are located mainly in the parietal, temporal and occipital lobes. The ascending pathways into the sensory cortex come primarily from relay sensory nuclei in the thalamus.
Primary sensory zones - these are areas of the sensory cortex, irritation or destruction of which causes clear and constant changes in the sensitivity of the organism (the nucleus of the analyzers according to I.P. Pavlov). They are composed of monomodal neurons and form sensations of the same quality. In the primary sensory zones, there is usually a clear spatial (topographic) representation of body parts, their receptor fields.
The primary projection zones of the cortex consist mainly of neurons of the 4th afferent layer, which are characterized by a clear topical organization. A significant proportion of these neurons are of the highest specificity. So, for example, the neurons of the visual areas selectively respond to certain signs of visual stimuli: some to shades of color, others to the direction of movement, and still others to the nature of the lines (edge, stripe, slope of the line), etc. However, it should be noted that the primary zones of individual areas of the cortex also include multimodal neurons that respond to several types of stimuli. In addition, there are also neurons, the reaction of which reflects the impact of nonspecific (limbic-reticular, or modulating) systems.
Secondary sensory areas located around the primary sensory zones, less localized, their neurons respond to the action of several stimuli, i.e. they are polymodal.
Localization of sensory zones. The most important sensory area is parietal lobe postcentral gyrus and the corresponding part of the paracentral lobule on the medial surface of the hemispheres. This area is designated as somatosensory areaI. There is a projection of the skin sensitivity of the opposite side of the body from tactile, pain, temperature receptors, interoceptive sensitivity and sensitivity of the musculoskeletal system - from muscle, articular, tendon receptors (Fig. 2).
Rice. 2. Diagram of sensory and motor homunculi
(after W. Penfield, T. Rasmussen). Frontal plane section of the hemispheres:
a- projection of general sensitivity in the cortex of the postcentral gyrus; b- projection of the motor system in the cortex of the precentral gyrus
In addition to the somatosensory region I, there are somatosensory area II smaller, located at the border of the intersection of the central groove with the upper edge temporal lobe, deep in the lateral groove. The accuracy of localization of body parts is less pronounced here. A well-studied primary projection area is auditory cortex(fields 41, 42), which is located deep in the lateral groove (cortex of the transverse temporal gyri of Heschl). The projection cortex of the temporal lobe also includes the center of the vestibular analyzer in the superior and middle temporal gyri.
V occipital lobe situated primary visual area(bark of a part of the wedge-shaped gyrus and lingular lobule, field 17). Here there is a topical representation of the retinal receptors. Each point of the retina corresponds to its own section of the visual cortex, while the area of the macula has a relatively large area of representation. Due to the incomplete intersection of the visual pathways, the retina halves of the same name are projected into the visual area of each hemisphere. The presence in each hemisphere of the projection of the retina of both eyes is the basis of binocular vision. Bark is located near field 17 secondary visual area(fields 18 and 19). The neurons of these zones are polymodal and respond not only to light, but also to tactile and auditory stimuli. In this visual area, a synthesis of various types of sensitivity occurs, more complex visual images and their identification appear.
In the secondary zones, the leading are the 2nd and 3rd layers of neurons, for which the bulk of information about the environment and the internal environment of the body, which has entered the sensory cortex, is transmitted for its further processing to the associative cortex, after which it is initiated (if necessary) behavioral reaction with the obligatory participation of the motor cortex.
Motor zones of the cortex. There are primary and secondary motor zones.
V primary motor zone (precentral gyrus, field 4) there are neurons that innervate the motor neurons of the muscles of the face, trunk and extremities. It has a clear topographic projection of the muscles of the body (see Fig. 2). The main regularity of topographic representation is that the regulation of muscle activity, providing the most accurate and varied movements (speech, writing, facial expressions), requires the participation of large areas of the motor cortex. Irritation of the primary motor cortex causes contraction of the muscles on the opposite side of the body (for the muscles of the head, contraction can be bilateral). With the defeat of this cortical zone, the ability to fine coordinated movements of the limbs, especially the fingers, is lost.
Secondary motor area (field 6) is located both on the lateral surface of the hemispheres, in front of the precentral gyrus (premotor cortex), and on the medial surface corresponding to the cortex of the superior frontal gyrus (additional motor area). Functionally, the secondary motor cortex is of paramount importance in relation to the primary motor cortex, realizing higher motor functions associated with the planning and coordination of voluntary movements. Here, to the greatest extent, a slowly increasing negative readiness potential, arising approximately 1 s before the start of the movement. The cortex of field 6 receives the bulk of impulses from the basal ganglia and cerebellum, and participates in the recoding of information about the plan of complex movements.
Irritation of the cortex of field 6 causes complex coordinated movements, for example, turning the head, eyes and trunk in the opposite direction, friendly contractions of the flexors or extensors on the opposite side. In the premotor cortex, there are motor centers associated with human social functions: the center of written speech in the posterior part of the middle frontal gyrus (field 6), Broca's motor speech center in the posterior part of the inferior frontal gyrus (field 44), providing speech praxis, as well as the musical motor center (field 45), providing the tonality of speech, the ability to sing. The neurons of the motor cortex receive afferent inputs through the thalamus from muscle, articular and cutaneous receptors, from the basal ganglia and cerebellum. The main efferent outlet of the motor cortex to the stem and spinal motor centers is the pyramidal cells of the V layer. The main lobes of the cerebral cortex are shown in Fig. 3.
Rice. 3. The four main lobes of the cerebral cortex (frontal, temporal, parietal and occipital); side view. They contain the primary motor and sensory areas, motor and sensory areas of a higher order (second, third, etc.) and the associative (nonspecific) cortex.
Associative areas of the cortex(nonspecific, intersensory, inter-analytic cortex) include areas of the neocortex that are located around the projection areas and next to the motor areas, but do not directly perform sensory or motor functions, therefore, they cannot be attributed primarily to sensory or motor functions, the neurons of these areas have large learning ability. The boundaries of these areas are not clearly marked. The associative cortex is the phylogenetically youngest part of the neocortex, which is most developed in primates and humans. In humans, it makes up about 50% of the entire cortex, or 70% of the neocortex. The term "associative cortex" arose in connection with the existing idea that these zones, due to the cortico-cortical connections passing through them, connect the motor zones and at the same time serve as a substrate for higher mental functions. The main associative zones of the cortex are: the parietotemporal-occipital, prefrontal cortex of the frontal lobes and the limbic associative zone.
The neurons of the associative cortex are polysensory (polymodal): they usually respond not to one (like the neurons of the primary sensory zones), but to several stimuli, that is, the same neuron can be excited upon stimulation of auditory, visual, skin and other receptors. The polysensory nature of neurons in the associative cortex is created by cortical-cortical connections with different projection zones, connections with the associative nuclei of the thalamus. As a result, the associative cortex is a kind of collector of various sensory stimuli and is involved in the integration of sensory information and in ensuring the interaction of sensory and motor areas of the cortex.
The associative areas occupy the 2nd and 3rd cellular layers of the associative cortex, where powerful unimodal, multi-modal and nonspecific afferent streams meet. The work of these parts of the cerebral cortex is necessary not only for the successful synthesis and differentiation (selective discrimination) of stimuli perceived by a person, but also for the transition to the level of their symbolization, that is, for operating with the meanings of words and using them for abstract thinking, for the synthetic nature of perception.
Since 1949, D. Hebb's hypothesis has become widely known, postulating the coincidence of presynaptic activity with the discharge of a post-synaptic neuron as a condition for synaptic modification, since not all synapse activity leads to the excitation of a postsynaptic neuron. Based on the hypothesis of D. Hebb, it can be assumed that individual neurons of the associative zones of the cortex are connected by various pathways and form cellular ensembles that distinguish "patterns", i.e. corresponding to unitary forms of perception. These connections, as D. Hebb noted, are so well developed that it is enough to activate one neuron, as the whole ensemble is excited.
The apparatus that plays the role of a regulator of the level of wakefulness, as well as selectively modulates and actualizes the priority of a particular function, is the modulating system of the brain, which is often called the limbic-reticular complex, or the ascending activating system. The nerve formations of this apparatus include the limbic and nonspecific systems of the brain with activating and inactivating structures. Among the activating formations, the reticular formation of the midbrain, the posterior hypothalamus, and the blue spot in the lower parts of the brain stem are primarily distinguished. Inactivating structures include the preoptic region of the hypothalamus, the nucleus of the suture in the brainstem, and the frontal cortex.
Currently, according to thalamocortical projections, it is proposed to distinguish three main associative systems of the brain: thalamophenous, thalamophobic and thalamotemporal.
Thalamo-parietal system represented by the associative zones of the parietal cortex, receiving the main afferent inputs from the posterior group of the associative nuclei of the thalamus. The parietal associative cortex has efferent outputs to the nuclei of the thalamus and hypothalamus, to the motor cortex and the nucleus of the extrapyramidal system. The main functions of the thalamotemic system are gnosis and praxis. Under gnosis understand the function of various types of recognition: shapes, sizes, meanings of objects, understanding of speech, cognition of processes, patterns, etc. Gnostic functions include the assessment of spatial relationships, for example, the mutual arrangement of objects. In the parietal cortex, the center of stereognosis is distinguished, which provides the ability to recognize objects by touch. A variant of the gnostic function is the formation in the mind of a three-dimensional model of the body ("body schema"). Under praxis understand purposeful action. The praxis center is located in the supracortical gyrus of the left hemisphere; it provides storage and implementation of the program of motorized automated acts.
Thalamophobic system It is represented by the associative zones of the frontal cortex, which have the main afferent input from the associative mediodorsal nucleus of the thalamus and other subcortical nuclei. The main role of the frontal associative cortex is reduced to the initiation of basic systemic mechanisms for the formation of functional systems of purposeful behavioral acts (P.K. Anokhin). The prefrontal area plays a major role in developing a strategy of behavior. The violation of this function is especially noticeable when it is necessary to quickly change the action and when some time passes between the formulation of the problem and the beginning of its solution, i.e. stimuli have time to accumulate, requiring the correct inclusion in a holistic behavioral response.
Thalamotemporal system. Some associative centers, for example, stereognosis, praxis, also include areas of the temporal cortex. In the temporal cortex is the auditory center of Wernicke's speech, located in the posterior parts of the superior temporal gyrus of the left hemisphere. This center provides speech gnosis: recognition and storage of oral speech, both one's own and someone else's. In the middle part of the superior temporal gyrus, there is a recognition center for musical sounds and their combinations. On the border of the temporal, parietal and occipital lobes there is a reading center, which provides recognition and storage of images.
An essential role in the formation of behavioral acts is played by the biological quality of an unconditioned reaction, namely its importance for the preservation of life. In the process of evolution, this meaning was fixed in two opposite emotional states - positive and negative, which in humans form the basis of his subjective experiences - pleasure and displeasure, joy and sadness. In all cases, purposeful behavior is built in accordance with the emotional state that arose under the action of the stimulus. During behavioral reactions of a negative nature, the tension of the autonomic components, especially the cardiovascular system, in some cases, especially in continuous so-called conflict situations, can reach great strength, which causes a violation of their regulatory mechanisms (autonomic neuroses).
In this part of the book, the main general issues of the analytic-synthetic activity of the brain are considered, which will allow us to move in the subsequent chapters to an exposition of particular issues of the physiology of sensory systems and higher nervous activity.
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- 1) at the beginning of the 19th century. F. Gall suggested that the substrate for various psychic "abilities" (honesty, frugality, love, etc.))) are small areas of n. shopping mall KBPs that grow with the development of these abilities. Gall believed that various abilities have a clear localization in the GM and that they can be determined by the protrusions on the skull, where the corresponding to the given ability, n. shopping mall and begins to bulge, while forming a tubercle on the skull.
- 2) In the 40s of the XIX century. Gall is opposed by Flurance, who, on the basis of experiments on the extirpation (removal) of parts of the GM, puts forward a provision on the equipotentiality (from the Latin equus - "equal") of the KBP functions. In his opinion, GM is a homogeneous mass that functions as a single integral organ.
- 3) The French scientist P. Broca laid the foundation of the modern doctrine of the localization of functions in KBP, who in 1861 identified the motor center of speech. Subsequently, the German psychiatrist K. Wernicke in 1873 discovered the center of verbal deafness (impaired understanding of speech).
Since the 70s. The study of clinical observations has shown that the defeat of limited areas of the KBP leads to the predominant loss of quite specific mental functions. This gave rise to the allocation of separate areas in the PCB, which began to be considered as nerve centers responsible for certain mental functions.
Summarizing the observations carried out on the wounded with brain damage during the First World War, in 1934 the German psychiatrist K. Kleist drew up the so-called localization map, in which even the most complex mental functions were correlated with limited areas of the PCD. But the approach of direct localization of complex mental functions in certain areas of the CPD is untenable. An analysis of the facts of clinical observations showed that disorders of such complex mental processes as speech, writing, reading, counting, can occur with completely different lesions of the CPD. The defeat of limited areas of the cerebral cortex, as a rule, leads to disruption of a whole group of mental processes.
4) a new trend has emerged that considers mental processes as a function of the entire GM as a whole ("anti-localizationism"), but is untenable.
Through the work of I. M. Sechenov, and then I. P. Pavlov, the doctrine of the reflex foundations of mental processes and the reflex laws of the work of the KBP, it led to a radical revision of the concept of "function" - began to be considered as a set of complex temporary connections. The foundations were laid for new ideas about the dynamic localization of functions in the KBP.
Summing up, we can highlight the main provisions of the theory of systemic dynamic localization of higher mental functions:
- - each mental function is a complex functional system and is provided by the brain as a whole. Moreover, various brain structures make their own specific contribution to the implementation of this function;
- - various elements of the functional system can be located in areas of the brain that are quite distant from each other and, if necessary, replace each other;
- - when a certain part of the brain is damaged, a "primary" defect occurs - a violation of a certain physiological principle of work inherent in a given brain structure;
- - as a result of the defeat of a common link included in different functional systems, "secondary" defects may arise.
Currently, the theory of systemic dynamic localization of higher mental functions is the main theory explaining the relationship between the psyche and the brain.
Histological and physiological studies have shown that KBP is a highly differentiated apparatus. Different areas of the cerebral cortex have a different structure. The neurons of the cortex are often so specialized that from their number one can distinguish those that respond only to very special stimuli or to very special signs. A number of sensory centers are located in the cerebral cortex.
Localization is firmly established in the so-called "projection" zones - cortical fields directly connected by their paths with the underlying parts of the NS and the periphery. The functions of the KBP are more complex, phylogenetically younger, and cannot be narrowly localized; very extensive areas of the cortex, and even the entire cortex as a whole, are involved in the implementation of complex functions. At the same time, within the KBP there are areas, the lesion of which causes a varying degree, for example, speech disorders, disorders of gnosia and praxia, the topodiagnostic value of which is also significant.
Instead of representing the KBP as, to a certain extent, an isolated superstructure over other floors of the NS with narrowly localized, surface-connected (associative) and peripheral (projection) areas, I.P. Pavlov created the doctrine of the functional unity of neurons belonging to various parts of the nervous system - from receptors in the periphery to the cerebral cortex - the doctrine of analyzers. What we call the center is the higher, cortical, section of the analyzer. Each analyzer is associated with specific areas of the cerebral cortex
3) The doctrine of the localization of functions in the cerebral cortex developed in the interaction of two opposite concepts - anti-localizationism, or equiponticalism (Flurance, Lashley), which denies the localization of functions in the cortex, and narrow localization psychomorphologism, which tried in its extreme versions (Gall ) localize in limited areas of the brain even such mental qualities as honesty, secrecy, love for parents. Of great importance was the discovery by Fritsch and Gitzig in 1870 of areas of the cortex, the irritation of which caused a motor effect. Other researchers have also described areas of the cortex associated with skin sensitivity, vision, and hearing. Clinicians-neurologists and psychiatrists also testify to the violation of complex mental processes in focal brain lesions. The foundations of the modern view of the localization of functions in the brain were laid by Pavlov in his theory of analyzers and the theory of dynamic localization of functions. According to Pavlov, an analyzer is a complex, functionally unified neural ensemble that serves to decompose (analyze) external or internal stimuli into separate elements. It starts with a receptor at the periphery and ends in the cerebral cortex. Cortical centers are the cortical sections of the analyzers. Pavlov showed that the cortical representation is not limited to the projection zone of the corresponding conductors, going far beyond its limits, and that the cortical zones of various analyzers overlap each other. The result of Pavlov's research was the doctrine of the dynamic localization of functions, suggesting the possibility of the participation of the same nervous structures in the provision of various functions. Localization of functions means the formation of complex dynamic structures or combination centers, consisting of a mosaic of excited and inhibited far-removed points of the nervous system, united in a common work in accordance with the nature of the required end result. The doctrine of the dynamic localization of functions received its further development in the works of Anokhin, who created the concept of a functional system as a circle of certain physiological manifestations associated with the performance of a certain function. The functional system includes, each time, in different combinations, various central and peripheral structures: cortical and deep nerve centers, pathways, peripheral nerves, executive organs. The same structures can be included in many functional systems, which expresses the dynamism of the localization of functions. I.P. Pavlov believed that individual areas of the cortex have different functional significance. However, there are no strictly defined boundaries between these areas. Cells from one area move to neighboring areas. In the center of these areas are clusters of the most specialized cells, the so-called analyzer nuclei, and at the periphery, less specialized cells. In the regulation of body functions, not strictly outlined points are involved, but many nerve elements of the cortex. Analysis and synthesis of incoming impulses and the formation of a response to them are carried out by significantly larger areas of the cortex. According to Pavlov, the center is the brain end of the so-called analyzer. An analyzer is a nervous mechanism, the function of which is to decompose the known complexity of the external and internal world into separate elements, that is, to perform analysis. At the same time, thanks to the broad connections with other analyzers, the synthesizing of analyzers with each other and with different activities of the organism takes place here.
Significance of different parts of the cerebral cortex
brain.
2. Motor functions.
3. Functions of the cutaneous and proprioriceptive
sensitivity.
4. Auditory functions.
5. Visual functions.
6. Morphological foundations of localization of functions in
cerebral cortex.
The core of the motor analyzer
The auditory analyzer core
The core of the visual analyzer
The core of the flavor analyzer
Skin Analyzer Core
7. Bioelectric activity of the brain.
8. Literature.
THE IMPORTANCE OF VARIOUS SITES OF THE LARGE BARK
HEMISPHERE OF THE BRAIN
For a long time, there has been a dispute between scientists about the location (localization) of areas of the cerebral cortex associated with various functions of the body. The most diverse and mutually opposite points of view were expressed. Some believed that every function of our body corresponds to a strictly defined point in the cerebral cortex, while others denied the presence of any centers; They attributed any reaction to the entire cortex, considering it to be completely unambiguous in a functional sense. The method of conditioned reflexes made it possible for I.P. Pavlov to clarify a number of unclear questions and develop a modern point of view.
There is no strictly fractional localization of functions in the cerebral cortex. This follows from experiments on animals, when, after the destruction of certain areas of the cortex, for example, the motor analyzer, after a few days, neighboring areas take over the function of the destroyed area and the movements of the animal are restored.
This ability of the cortical cells to replace the function of the missing areas is associated with the great plasticity of the cerebral cortex.
I.P. Pavlov believed that individual areas of the cortex have different functional significance. However, there are no strictly defined boundaries between these areas. Cells from one area move to neighboring areas.
Figure 1. Diagram of the connection between the cortex and receptors.
1 - spinal cord or medulla oblongata; 2 - diencephalon; 3 - cerebral cortex
In the center of these areas are clusters of the most specialized cells, the so-called analyzer nuclei, and at the periphery, less specialized cells.
In the regulation of body functions, not strictly outlined points are involved, but many nerve elements of the cortex.
Analysis and synthesis of incoming impulses and the formation of a response to them are carried out by significantly larger areas of the cortex.
Consider some areas that are predominantly of one kind or another. A schematic location of the location of these areas is shown in Figure 1.
Motor functions. The cortical section of the motor analyzer is located mainly in the anterior central gyrus, anterior to the central (Roland) sulcus. In this area there are nerve cells, with the activity of which all movements of the body are associated.
The processes of large nerve cells located in the deep layers of the cortex descend into the medulla oblongata, where a significant part of them intersects, that is, passes to the opposite side. After the transition, they descend along the spinal cord, where the rest of them intersects. In the anterior horns of the spinal cord, they come into contact with the motor nerve cells located here. Thus, the excitation that has arisen in the cortex reaches the motor neurons of the anterior horns of the spinal cord and then through their fibers goes to the muscles. Due to the fact that in the oblong, and partly in the spinal cord, a transition (cross) of the motor paths to the opposite side occurs, the excitation that arose in the left hemisphere of the brain enters the right half of the body, and impulses from the right hemisphere enter the left half of the body. That is why hemorrhage, injury or any other damage to one of the sides of the cerebral hemispheres entails a violation of the motor activity of the muscles of the opposite half of the body.
Figure 2. Diagram of individual areas of the cerebral cortex.
1 - motor area;
2 - skin area
and proprioriceptive sensitivity;
3 - visual area;
4 - auditory area;
5 - gustatory area;
6 - olfactory area
In the anterior central gyrus, the centers innervating different muscle groups are located so that in the upper part of the motor region are the centers of movement of the lower extremities, then below the center of the muscles of the trunk, even below the center of the forelimbs and, finally, below all the centers of the muscles of the head.
The centers of different muscle groups are represented differently and occupy uneven areas.
Functions of cutaneous and proprioceptive sensitivity. The area of cutaneous and proprioceptive sensitivity in humans is located mainly behind the central (Roland) sulcus in the posterior central gyrus.
The localization of this area in humans can be established by the method of electrical stimulation of the cerebral cortex during operations. Irritation of various parts of the cortex and at the same time questioning the patient about the sensations that he experiences, make it possible to form a fairly clear idea of the indicated area. The so-called muscular feeling is associated with the same area. The impulses arising in the proprioceptor-receptors located in the joints, tendons and muscles mainly enter this part of the cortex.
The right hemisphere perceives impulses traveling along the centripetal fibers mainly from the left, and the left hemisphere mainly from the right half of the body. This explains the fact that a defeat, for example, of the right hemisphere will cause a violation of the sensitivity of the predominantly left side.
Auditory functions. The auditory area is located in the temporal lobe of the cortex. When the temporal lobes are removed, complex sound perceptions are disturbed, since the ability to analyze and synthesize sound perceptions is disturbed.
Visual functions. The visual area is located in the occipital lobe of the cerebral cortex. When the occipital lobes of the brain are removed, the dog experiences loss of vision. The animal does not see, bumps into objects. Only pupillary reflexes are preserved. In humans, a violation of the visual region of one of the hemispheres causes the loss of half of the vision of each eye. If the lesion touches the visual region of the left hemisphere, then the functions of the nasal part of the retina of one eye and the temporal part of the retina of the other eye fall out.
This feature of visual impairment is due to the fact that the optic nerves partially intersect on the way to the cortex.
Morphological foundations of dynamic localization of functions in the cerebral cortex (centers of the cerebral cortex).
Knowledge of the localization of functions in the cerebral cortex is of great theoretical importance, since it gives an idea of the nervous regulation of all body processes and its adaptation to the environment. It is also of great practical importance for the diagnosis of lesions in the cerebral hemispheres.
The concept of the localization of functions in the cerebral cortex is associated primarily with the concept of the cortical center. Back in 1874, the Kiev anatomist V. A, Betz made a statement that each area of the cortex differs in structure from other areas of the brain. This laid the foundation for the doctrine of the different quality of the cerebral cortex - cytoarchitectonics (cytos - cell, architectones - system). At present, it has been possible to identify more than 50 different parts of the cortex - cortical cytoarchitectonic fields, each of which differs from the others in the structure and location of nerve elements. From these fields, designated by numbers, a special map of the human cerebral cortex is compiled.
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about I.P. Pavlov, the center is the brain end of the so-called analyzer. An analyzer is a nervous mechanism, the function of which is to decompose the known complexity of the external and internal world into separate elements, that is, to perform analysis. At the same time, thanks to the broad connections with other analyzers, the synthesizing of analyzers with each other and with different activities of the organism takes place here.
Figure 3. Map of the cytoarchitectonic fields of the human brain (according to the Institute of Moeg of the Academy of Medical Sciences of the USSR) Above - the upper lateral surface, below - the medial surface. Explanation in the text.
Currently, the entire cerebral cortex is viewed as a continuous receiving surface. The cortex is a collection of the cortical ends of the analyzers. From this point of view, we will consider the topography of the cortical regions of the analyzers, that is, the most important perceiving areas of the cerebral cortex.
First of all, let us consider the cortical ends of the analyzers that perceive irritations from the internal environment of the body.
1. The nucleus of the motor analyzer, ie, the analyzer of proprioceptive (kinesthetic) stimulation emanating from bones, joints, skeletal muscles and their tendons, is located in the precentral gyrus (fields 4 and 6) and lobulus paracentralis. Here motor conditioned reflexes are closed. IP Pavlov explains the motor paralysis that occurs when the motor zone is damaged not by damage to motor efferent neurons, but by a violation of the motor analyzer nucleus, as a result of which the cortex does not perceive kinesthetic stimuli and movements become impossible. The cells of the motor analyzer nucleus are embedded in the middle layers of the motor cortex. In its deep layers (V, partly VI) lie giant pyramidal cells, which are efferent neurons, which I.P. Pavlov considers as intercalary neurons connecting the cerebral cortex with the subcortical nuclei, the nuclei of the cranial nerves and the anterior horns of the spinal cord, i.e. with motor neurons. In the precentral gyrus, the human body, as well as in the posterior gyrus, is projected upside down. In this case, the right motor region is connected with the left half of the body and vice versa, because the pyramidal pathways starting from it intersect partly in the oblong, and partly in the spinal cord. The muscles of the trunk, larynx, pharynx are influenced by both hemispheres. In addition to the precentral gyrus, proprioceptive impulses (muscle-articular sensitivity) also come to the cortex of the postcentral gyrus.
2. The nucleus of the motor analyzer, related to the combined rotation of the head and eyes in the opposite direction, is placed in the middle frontal gyrus, in the premotor region (field 8). Such a turn also occurs upon stimulation of field 17 located in the occipital lobe in the vicinity of the nucleus of the visual analyzer. Since, when the muscles of the eye contract, not only impulses from the receptors of these muscles, but also impulses from the receptors of these muscles (visual analyzer, field 77) always enter the cerebral cortex (motor analyzer, field 8), various visual stimuli are always combined with different positions eye, set by the contraction of the muscles of the eyeball.
3. The nucleus of the motor analyzer, through which the synthesis of purposeful complex professional, labor and sports movements occurs, is placed in the left (in right-handed) lower parietal lobe, in the gyrus supramarginalis (deep layers of field 40). These coordinated movements, formed according to the principle of temporary connections and developed by the practice of individual life, are carried out through the connection of the gyrus supramarginalis with the precentral gyrus. When field 40 is damaged, the ability to move in general remains, but there is an inability to perform purposeful movements, to act - apraxia (praxia - action, practice).
4. The nucleus of the analyzer of the position and movement of the head - the static analyzer (vestibular apparatus) in the cerebral cortex has not yet been precisely localized. There is reason to believe that the vestibular apparatus is projected in the same area of the cortex as the cochlea, that is, in the temporal lobe. So, with the defeat of fields 21 and 20, lying in the region of the middle and lower temporal gyri, ataxia is observed, that is, a disorder of balance, swaying of the body when standing. This analyzer, which plays a decisive role in man's upright posture, is of particular importance for the work of pilots in jet aircraft, since the sensitivity of the vestibular apparatus on an aircraft is significantly reduced.
5. The nucleus of the analyzer of impulses coming from the viscera and blood vessels is located in the lower parts of the anterior and posterior central gyri. Centripetal impulses from the viscera, blood vessels, involuntary muscles and glands of the skin enter this section of the cortex, from where centrifugal paths depart to the subcortical vegetative centers.
In the premotor area (fields 6 and 8), the unification of autonomic functions takes place.
Nerve impulses from the external environment of the body enter the cortical ends of the analyzers of the external world.
1. The nucleus of the auditory analyzer lies in the middle part of the superior temporal gyrus, on the surface facing the insula - fields 41, 42, 52, where the cochlea is projected. The damage leads to deafness.
2. The nucleus of the visual analyzer is located in the occipital lobe - fields 18, 19. On the inner surface of the occipital lobe, along the edges of the sulcus Icarmus, the visual pathway ends in field 77. The retina of the eye is projected here. When the nucleus of the visual analyzer is damaged, blindness occurs. Above field 17, field 18 is located, with the defeat of which vision is preserved and only visual memory is lost. Even higher is the field, when it is defeated, the orientation in the unfamiliar environment is lost.
3. The nucleus of the gustatory analyzer, according to some data, is located in the inferior postcentral gyrus, close to the centers of the muscles of the mouth and tongue, according to others, in the immediate vicinity of the cortical end of the olfactory analyzer, which explains the close connection between olfactory and gustatory senses. It has been established that a taste disorder occurs when field 43 is affected.
The analyzers of smell, taste and hearing of each hemisphere are connected to the receptors of the corresponding organs on both sides of the body.
4. The nucleus of the skin analyzer (tactile, pain and temperature sensitivity) is located in the postcentral gyrus (fields 7, 2, 3) and in the neuperior parietal region (fields 5 and 7).
A particular type of skin sensitivity - recognizing objects by touch - stereognosia (stereos - spatial, gnosis - knowledge) is connected with a section of the upper parietal lobe cortex (field 7) crosswise: the left hemisphere corresponds to the right hand, the right - to the left hand. When the surface layers of field 7 are affected, the ability to recognize objects by touch is lost with closed eyes.
Bioelectric activity of the brain.
The derivation of the biopotentials of the brain - electroencephalography - gives an idea of the level of physiological activity of the brain. In addition to the method of electroencephalography-recording of bioelectric potentials, the method of encephaloscopy-registration of fluctuations in the brightness of the luminescence of many points of the brain (from 50 to 200) is used.
An electroencephalogram is an integrative spatio-temporal indicator of spontaneous electrical activity in the brain. It distinguishes between the amplitude (range) of oscillations in microvolts and the frequency of oscillations in hertz. In accordance with this, four types of waves are distinguished in the electroencephalogram: -, -, - and -rhythms. The -rhythm is characterized by frequencies in the range of 8-15 Hz, with an oscillation amplitude of 50-100 μV. It is recorded only in humans and higher apes in a state of wakefulness, with closed eyes and in the absence of external stimuli. Visual stimuli inhibit the -rhythm.
In some people with a vivid visual imagination, the -rhythm may be absent altogether.
An active brain is characterized by a (-rhythm. These are electrical waves with an amplitude of 5 to 30 μV and a frequency of 15 to 100 Hz. It is well recorded in the frontal and central regions of the brain. The -rhythm appears during sleep. emotions, painful conditions The frequency of the-rhythm potentials is from 4 to 8 Hz, the amplitude is from 100 to 150 μV During sleep, the -rhythm also appears - slow (with a frequency of 0.5-3.5 Hz), high-amplitude (up to 300 μV ) fluctuations in the electrical activity of the brain.
In addition to the considered types of electrical activity, an E-wave (a wave of expectation of a stimulus) and spindle-shaped rhythms are recorded in a person. A wave of expectation is registered when performing conscious, expected actions. It precedes the appearance of the expected stimulus in all cases, even with its repeated repetition. Apparently, it can be considered as an electroencephalographic correlate of an action acceptor, which ensures the anticipation of the results of an action before its completion. Subjective readiness to respond to the action of a stimulus in a strictly defined way is achieved by a psychological attitude (D.N. Uznadze). Fusiform rhythms of variable amplitude, with a frequency of 14 to 22 Hz, appear during sleep. Various forms of life activity lead to a significant change in the rhythms of the bioelectric activity of the brain.
With mental work, the -rhythm increases, while the -rhythm disappears. During muscular work of a static nature, there is a desynchronization of the electrical activity of the brain. Fast oscillations with low amplitude appear. During dynamic operation, ne-. The periods of desynchronized and synchronized activity are observed, respectively, during the moments of work and rest.
The formation of a conditioned reflex is accompanied by desynchronization of brain wave activity.
Desynchronization of waves occurs during the transition from sleep to wakefulness. In this case, the spindle-shaped rhythms of sleep are replaced
-rhythm, the electrical activity of the reticular formation increases. Synchronization (identical in phase and direction of the wave)
characteristic of the braking process. It is most pronounced when the reticular formation of the brain stem is turned off. Electroencephalogram waves, according to most researchers, are the result of the summation of inhibitory and excitatory postsynaptic potentials. The electrical activity of the brain is not a simple reflection of metabolic processes in the nervous tissue. It has been established, in particular, that in the impulse activity of individual clusters of nerve cells, signs of acoustic and semantic codes are found.
In addition to specific nuclei of the thalamus, associative nuclei arise and develop, which have connections with the neocortex and determine the development of the telencephalon. The third source of afferent influences on the cerebral cortex is the hypothalamus, which plays the role of the highest regulatory center of autonomic functions. In mammals, phylogenetically more ancient parts of the anterior hypothalamus are associated with ...
The formation of conditioned reflexes becomes difficult, memory processes are disturbed, selectivity of reactions is lost and their immoderate increase is noted. The large brain consists of almost identical halves - the right and left hemispheres, which are connected by the corpus callosum. Commissural fibers connect symmetrical areas of the cortex. However, the cortex of the right and left hemispheres is not symmetrical, not only externally, but also ...
The approach to assessing the mechanisms of work of the higher parts of the brain using conditioned reflexes was so successful that it allowed Pavlov to create a new branch of physiology - "Physiology of higher nervous activity", the science of the mechanisms of work of the cerebral hemispheres. UNCONDITIONAL AND CONDITIONAL REFLEXES The behavior of animals and humans is a complex system of interrelated ...
The cortex of the cerebral hemispheres is the evolutionarily youngest formation that has reached the greatest values in humans in relation to the rest of the brain mass. In humans, the mass of the cerebral cortex averages 78% of the total mass of the brain. The cerebral cortex is extremely important in the regulation of the body's vital activity, the implementation of complex forms of behavior and in the formation of neuropsychic functions. These functions are provided not only by the entire mass of the cortical substance, but also by the unlimited possibilities of associative connections between the cells of the cortex and subcortical formations, which creates conditions for the most complex analysis and synthesis of incoming information, for the development of forms of learning that are inaccessible to animals.
Speaking about the leading role of the cerebral cortex in neurophysiological processes, one should not forget that this higher section can function normally only in close interaction with the subcortical formations. The juxtaposition of the cortex and the underlying parts of the brain is largely schematic and conditional. In recent years, ideas have been developing about the vertical organization of the functions of the nervous system, about the annular cortical-subcortical connections.
The cells of the cortical substance are much less specialized than the nuclei of the subcortical formations. It follows that the compensatory capabilities of the cortex are very high - the functions of the affected cells can be taken over by other neurons; the defeat of rather significant areas of the cortical substance can be clinically very blurred (the so-called clinical silent zones). The lack of a narrow specialization of cortical neurons creates conditions for the emergence of a wide variety of interneuronal connections, the formation of complex "ensembles" of neurons that regulate various functions. This is the most important foundation of learning ability. The theoretically possible number of connections between 14 billion cells of the cerebral cortex is so great that a significant part of them remains unused during a person's life. This once again confirms the unlimited possibilities of human learning.
Despite the well-known nonspecificity of cortical cells, certain groups of them are anatomically and functionally more closely related to certain specialized parts of the nervous system. The morphological and functional ambiguity of various parts of the cortex allows us to talk about the cortical centers of vision, hearing, touch, etc., which have a certain localization. In the works of researchers of the 19th century, this principle of localization was taken to an extreme: attempts were made to identify the centers of will, thinking, the ability to understand art, etc. At present, it would be incorrect to speak of the cortical center as a strictly limited group of cells. It should be noted that the specialization of nerve links is formed in the process of life.
According to IP Pavlov, the brain center, or cortical section of the analyzer, consists of a "nucleus" and "scattered elements." The "nucleus" is a group of cells, relatively homogeneous in morphological terms, with an accurate projection of the receptor fields. The "scattered elements" are located in a circle or at a certain distance from the "core": they carry out a more elementary and less differentiated analysis and synthesis of the incoming information.
Of the 6 layers of cortical cells, the upper layers are most developed in humans in comparison with similar layers in animals and are formed in ontogenesis much later than the lower layers. The lower layers of the cortex have connections with peripheral receptors (IV layer) and muscles (V layer) and are called “primary” or “projection” cortical zones due to their direct connection with the peripheral parts of the analyzer. Above the "primary" zones, systems of "secondary" zones (layers II and III) are built up, in which associative connections with other parts of the cortex prevail, therefore they are also called projection-associative.
Thus, in the cortical representations of the analyzers, two groups of cell zones are revealed. Such a structure is found in the occipital zone, where the visual pathways are projected, in the temporal zone, where the auditory pathways end, in the posterior central gyrus - the cortical part of the sensitive analyzer, in the anterior central gyrus - the cortical motor center. The anatomical heterogeneity of the "primary" and "secondary" zones is accompanied by physiological differences. Experiments with irritation of the cortex have shown that the excitation of the primary zones of the sensory divisions leads to the emergence of elementary sensations. For example, irritation of the occipital parts causes a sensation of flickering of light points, dashes, etc. When secondary zones are irritated, more complex phenomena arise: the subject sees variously designed objects - people, birds, etc. It can be assumed that it is in the secondary zones that operations are carried out gnosis and partly praxis.
In addition, tertiary zones, or zones of overlapping of the cortical representations of individual analyzers, are distinguished in the cortical substance. In humans, they occupy a very significant place and are located primarily in the parietotemporal-occipital region and in the frontal zone. Tertiary zones enter into extensive connections with cortical analyzers and thereby ensure the development of complex, integrative reactions, among which meaningful actions take the first place in humans. In the tertiary zones, therefore, planning and control operations take place, requiring the complex participation of different parts of the brain.
In early childhood, the functional zones of the cortex overlap each other, their boundaries are diffuse, and only in the process of practical activity there is a constant concentration of functional zones in outlined, separated from each other centers. In the clinic, adult patients have very constant symptom complexes when certain areas of the cortex and associated nerve pathways are damaged.
In childhood, due to incomplete differentiation of functional zones, focal lesions of the cerebral cortex may not have a clear clinical manifestation, which should be remembered when assessing the severity and boundaries of brain damage in children.
In functional terms, the main integrative levels of cortical activity can be distinguished.
The first signaling system is associated with the activity of individual analyzers and implements the primary stages of gnosis and praxis, i.e., the integration of signals coming through the channels of individual analyzers and the formation of responses taking into account the state of the external and internal environment, as well as past experience. This first level can be attributed to the visual perception of objects with a concentration of attention on certain of its details, voluntary movements with their active strengthening or inhibition.
A more complex functional level of cortical activity unites the systems of various analyzers, includes a second signaling system) ", unites the systems of various analyzers, making it possible to perceive the environment in a meaningful way, to relate to the surrounding world" with knowledge and understanding. "This level of integration is closely related to speech activity, and understanding of speech (speech gnosis) and the use of speech as a means of circulation and thinking (speech praxis) are not only interrelated, but also due to various neurophysiological mechanisms, which is of great clinical importance.
The highest level of integration is formed in a person in the process of his maturation as a social being, in the process of mastering the skills and knowledge that society has.
The third stage of cortical activity plays the role of a kind of dispatcher of complex processes of higher nervous activity. It ensures the purposefulness of certain acts, creating conditions for their best implementation. This is achieved by "filtering" signals that are of the greatest importance at the moment, from secondary signals, by probabilistic forecasting of the future and the formation of promising tasks.
Of course, complex cortical activity could not have been carried out without the participation of an information storage system. Therefore, memory mechanisms are one of the most important components of this activity. In these mechanisms, not only the functions of fixing information (memorization) are of significant importance, but also the functions of obtaining the necessary information from the "storages" of memory (memory), as well as the functions of transferring information flows from blocks of random access memory (what is needed at the moment) to long-term memory blocks and vice versa. Otherwise, it would be impossible to assimilate new things, since old skills and knowledge would interfere with this.
Recent neurophysiological studies have made it possible to establish which functions are predominantly characteristic of certain parts of the cerebral cortex. Even in the last century, it was known that the occipital region of the cortex is closely connected with the visual analyzer, the temporal region - with the auditory (Heschl gyrus), the taste analyzer, the anterior central gyrus - with the motor, the posterior central gyrus - with the musculocutaneous analyzer. It can be conditionally considered that these departments are associated with the first type, cortical activity and provide the simplest forms of gnosis and praxis.
In the formation of more complex gnostic-praxical functions, the sections of the cortex that lie in the parietotemporal-occipital region take an active part. The defeat of these areas leads to more complex forms of disorders. In the temporal lobe of the left hemisphere is Wernicke's gnostic speech center. The motor center of speech is located somewhat anterior to the lower third of the anterior central gyrus (Broca's center). In addition to the centers of oral speech, there are sensory and motor centers of writing and a number of other formations, one way or another associated with speech. The parietotemporal-occipital region, where the paths coming from various analyzers are closed, is of paramount importance for the formation of higher mental functions. The renowned neurophysiologist and neurosurgeon W. Penfield called this area the interpretive cortex. In this area, there are also formations that take part in the mechanisms of memory.
Particular importance is attached to the frontal region. According to modern concepts, it is this part of the cerebral cortex that takes an active part in the organization of purposeful activity, in long-term planning and purposefulness, that is, it belongs to the third type of cortical functions.
The main centers of the cerebral cortex. Frontal lobe. The motor analyzer is located in the anterior central gyrus and paracentral lobule (fields 4, 6 and 6a according to Brodmann). In the middle layers there is an analyzer of kinesthetic irritations coming from skeletal muscles, tendons, joints and bones. In layer V and partly in layer VI, giant Betz pyramidal cells are located, the fibers of which form a pyramidal pathway. The anterior central gyrus has a certain somatotopic projection and is associated with the opposite half of the body. In the upper parts of the gyrus, the muscles of the lower extremities are projected, in the lower ones - of the face. The trunk, larynx, pharynx are represented in both hemispheres (Fig. 55).
The center of rotation of the eyes and head in the opposite direction is located in the middle frontal gyrus in the premotor region (fields 8, 9). The work of this center is closely connected with the system of the posterior longitudinal bundle, vestibular nuclei, formations of the striopallidal system involved in the regulation of torsion, as well as with the cortical part of the visual analyzer (field 17).
In the posterior parts of the superior frontal gyrus, the center is presented, giving rise to the frontal-cerebellopontine pathway (field 8). This area of the cerebral cortex is involved in ensuring the coordination of movements associated with upright posture, maintaining balance while standing, sitting, and regulates the work of the opposite hemisphere of the cerebellum.
The motor center of speech (the center of speech praxis) is located in the posterior part of the inferior frontal gyrus - Broca's gyrus (field 44). The center provides analysis of kinesthetic impulses from the muscles of the speech motor apparatus, storage and implementation of "images" of speech automatisms, the formation of oral speech, is closely related to the location behind it of the lower part of the anterior central gyrus (the projection zone of the lips, tongue and larynx) and with anterior to it musical motor center.
Musical motor center (field 45) provides a certain key, speech modulation, as well as the ability to compose musical phrases and sing.
The center of written speech is localized in the posterior part of the middle frontal gyrus in the immediate vicinity of the projection cortical zone of the hand (field 6). The center provides automatic writing and is functionally linked to Broca's center.
Parietal lobe. The center of the skin analyzer is located in the posterior central gyrus of fields 1, 2, 3 and the cortex of the superior parietal region (fields 5 and 7). In the posterior central gyrus, the tactile, painful, temperature sensitivity of the opposite half of the body is projected. In the upper sections, the sensitivity of the leg is projected, in the lower sections - the sensitivity of the face. Fields 5 and 7 show the deep sensitivities. Behind the middle sections of the posterior central gyrus is the center of stereognosis (fields 7.40 and partly 39), which provides the ability to recognize objects by touch.
The center is located posterior to the upper parts of the posterior central gyrus, which provides the ability to recognize one's own body, its parts, their proportions and mutual position (field 7).
The center of praxis is localized in the inferior parietal lobe on the left, supra-marginal gyrus (fields 40 and 39). The center provides storage and implementation of images of motor automatisms (praxis functions).
The center of the analyzer of interoceptive impulses of internal organs and vessels is located in the lower parts of the anterior and posterior central gyri. The center has close ties with subcortical vegetative formations.
The temporal lobe. The center of the auditory analyzer is located in the middle part of the superior temporal gyrus, on the surface facing the insula (Heschl gyrus, fields 41, 42, 52). These formations provide the projection of the cochlea, as well as the storage and recognition of auditory images.
The center of the vestibular analyzer (fields 20 and 21) is located in the lower parts of the outer surface of the temporal lobe, is projection, is in close connection with the lower basal parts of the temporal lobes, which give rise to the occipital-temporal cortical-cerebellopontine pathway.
Rice. 55. Scheme of localization of functions in the cerebral cortex (A - D). I - projection motor zone; II - the center of turning the eyes and head in the opposite direction; III - projection sensitivity zone; IV - projection visual zone; projection gnostic zones: V - hearing; VI - smell, VII - taste, VIII - gnostic zone of the body scheme; IX - stereognosis zone; X - gnostic visual zone; XI - Gnostic reading area; XII - Gnostic speech zone; XIII - praxis zone; XIV - praxical speech zone; XV - praxical writing zone; XVI - zone of control over the function of the cerebellum.
The center of the olfactory analyzer is located in the phylogenetically most ancient part of the cerebral cortex - in the hook and ammonium horn (field 11a, e) and provides a projection function, as well as storage and recognition of olfactory images.
The center of the gustatory analyzer is located in the immediate vicinity of the center of the olfactory analyzer, i.e., in the hook and horn of the ammonia, but, in addition, in the lowest part of the posterior central gyrus (field 43), as well as in the insula. Like the olfactory analyzer, the center provides projection function, storage and recognition of taste patterns.
The acoustical-gnostic sensory center of speech (Wernicke's center) is localized in the posterior parts of the superior temporal gyrus on the left, deep in the lateral groove (field 42, as well as fields 22 and 37). The center provides recognition and storage of sound images of oral speech, both one's own and someone else's.
In the immediate vicinity of the center of Wernicke (middle third of the superior temporal gyrus - field 22), there is a center that provides recognition of musical sounds and melodies.
Occipital lobe. The center of the visual analyzer is located in the occipital lobe (fields 17, 18, 19). Field 17 is a projection visual area, fields 18 and 19 provide storage and recognition of visual images, visual orientation in an unfamiliar environment.
On the border of the temporal, occipital and parietal lobes is the center of the analyzer of written speech (field 39), which is closely connected with the Wernicke center of the temporal lobe, with the center of the visual analyzer of the occipital lobe, as well as with the centers of the parietal lobe. The Reading Center provides recognition and storage of written speech patterns.
The data on the localization of functions were obtained either as a result of stimulation of various parts of the cortex in the experiment, or as a result of the analysis of disturbances arising from damage to certain parts of the cortex. Both of these approaches can only indicate the participation of certain cortical zones in certain mechanisms, but do not at all mean their strict specialization, an unambiguous connection with strictly defined functions.
In a neurological clinic, in addition to signs of damage to areas of the cerebral cortex, there are symptoms of irritation of its individual areas. In addition, in childhood, the phenomena of delayed or impaired development of cortical functions are observed, which largely modifies the "classic" symptomatology. The existence of different functional types of cortical activity determines different symptoms of cortical lesions. Analysis of this symptomatology allows us to identify the nature of the lesion and its localization.
Depending on the types of cortical activity, it is possible to distinguish among cortical lesions disturbances of gnosis and praxis at different levels of integration; speech disorders due to their practical importance; disorders of the regulation of purposefulness, purposefulness of neurophysiological functions. With each type of disorder, the memory mechanisms involved in this functional system can also be impaired. In addition, more total memory impairments are possible. In addition to relatively local cortical symptoms, more diffuse symptoms are observed in the clinic, manifested primarily in intellectual disability and in behavioral disorders. Both of these disorders are of particular importance in child psychiatry, although, in fact, many variants of such disorders can be considered borderline between neurology, psychiatry and pediatrics.
The study of cortical functions in childhood has a number of differences from the study of other parts of the nervous system. It is important to establish contact with the child, maintain a relaxed tone of conversation with him. Since many of the diagnostic tasks presented to the child are very difficult, you need to strive so that he not only understands the task, but also becomes interested in it. Sometimes, when examining overly distracted, motor disinhibited, or mentally retarded children, it takes a lot of patience and ingenuity to identify any abnormalities. In many cases, the analysis of the child's cortical functions is helped by the parents' reports about his behavior at home, at school, and school characteristics.
In the study of cortical functions, a psychological experiment is of great importance, the essence of which is the presentation of standardized goal-oriented tasks. Certain psychological techniques make it possible to assess certain aspects of mental activity in isolation, others - in a more comprehensive way. These include the so-called personality tests.
Gnosis and its disorders... Gnosis literally means recognition. Our orientation in the world around us is associated with recognizing the shape, size, spatial relationship of objects and, finally, with understanding their meaning, which is contained in the name of the object. This store of information about the world around us consists of the analysis and synthesis of streams of sensory impulses and is deposited in memory systems. The receptor apparatus and the transmission of sensory impulses with lesions of the higher gnostic mechanisms are preserved, but the interpretation of these impulses, the comparison of the received data with the images stored in the memory, are violated. As a result, there is a disorder of gnosis - agnosia, the essence of which is that while the perception of objects is preserved, the feeling of their "familiarity" is lost and the surrounding world, previously so familiar in details, becomes alien, incomprehensible, devoid of meaning.
But gnosis cannot be imagined as a simple comparison, image recognition. Gnosis is a process of continuous updating, clarification, concretization of the image stored in the memory matrix, under the influence of re-matching it with the received information.
Total agnosia in which there is complete disorientation, it is rare. Much more often gnosis is disturbed in any one analytic system, and, depending on the degree of damage, the severity of agnosia is different.
Visual agnosias occur when the occipital cortex is affected. The patient sees the object, but does not recognize it. There may be various options here. In some cases, the patient correctly describes the external properties of the object (color, shape, size), but cannot recognize the object. For example, the patient describes an apple as “something round, pink”, not recognizing an apple in an apple. But if you give the patient this object in hand, then he recognizes it by feeling. There are times when the patient does not recognize familiar faces. Some patients with a similar disorder are forced to remember people for some other reason (clothing, birthmark, etc.). In other cases, the agnosium patient recognizes the object, names its properties and function, but cannot remember what it is called. These cases belong to the group of speech disorders.
In some forms of visual agnosia, spatial orientation and visual memory are impaired. In practice, even when the object is not recognized, one can speak of violations of memory mechanisms, since the perceived object cannot be compared with its image in the gnostic matrix. But there are also cases when, upon re-presentation of the object, the patient says that he has already seen it, although he still cannot recognize it. In case of violations of the same spatial orientation, the patient not only does not recognize previously familiar faces, houses, etc., but can also walk in the same place many times without knowing it.
Often, with visual agnosia, the recognition of letters and numbers also suffers, and there is a loss of the ability to read. An isolated type of this disorder will be analyzed in the analysis of speech function.
A set of objects is used to study visual gnosis. Presenting them to the examinee, they are asked to determine, describe their appearance, compare which objects are larger and which are smaller. A set of pictures, color, solid and contour, is also used. They evaluate not only the recognition of objects, faces, but also plots. Along the way, you can check the visual memory: present several pictures, then mix them with previously not shown and ask the child to choose familiar pictures. At the same time, work time, persistence, fatigue are also taken into account.
It should be borne in mind that children recognize outline pictures worse than color and solid ones. Understanding the plot is related to the age of the child and the degree of mental development. At the same time, agnosias in the classical form in children are rare due to incomplete differentiation of cortical centers.
Auditory agnosias. They arise when the temporal lobe is affected in the area of the Heshl gyrus. The patient cannot recognize previously familiar sounds: the ticking of a clock, the ringing of a bell, the noise of pouring water. Possible violations of the recognition of musical melodies - amusia. In some cases, the definition of the direction of sound is violated. With some types of auditory agnosia, the patient is not able to distinguish the frequency of sounds, for example, the beat of a metronome.
Sensitive agnosias are caused by impaired recognition of tactile, painful, temperature, proprioceptive images or their combinations. They occur when the parietal region is affected. This includes astereognosis, body schema disorders. In some variants of astereognosis, the patient not only cannot determine the object by touch, but also cannot determine the shape of the object, the peculiarity of its surface. Sensitive agnosia also includes anosognosia, in which the patient is not aware of his defect, such as paralysis. Phantom sensations can be attributed to disturbances in sensitive gnosis.
When examining children, it should be borne in mind that a small child cannot always correctly show parts of his body; the same applies to patients suffering from dementia. In such cases, of course, it is not necessary to talk about a disorder of the body scheme.
Taste and olfactory agnosias are rare. In addition, the recognition of smells is very individual, in many respects related to the personal experience of a person.
Praxis and his disorders... Praxis is understood as purposeful action. A person learns in the process of life a lot of special motor acts. Many of these skills, being formed with the participation of higher cortical mechanisms, are automated and become the same inherent human ability as simple movements. But when the cortical mechanisms involved in the implementation of these acts are damaged, peculiar movement disorders arise - apraxia, in which there is no paralysis, no disturbances in tone or coordination, and even simple voluntary movements are possible, but more complex, purely human motor acts are disturbed. The patient suddenly turns out to be unable to perform such seemingly simple actions as shaking hands, buttoning buttons, combing, lighting a match, etc. Apraxia occurs primarily when the parieto-temporal-occipital region of the dominant hemisphere is affected. In this case, both halves of the body are affected. Apraxia can also occur with lesions of the subdominant right hemisphere (in right-handers) and the corpus callosum, which connects both hemispheres. In this case, apraxia is determined only on the left. With apraxia, the plan of action suffers, that is, the compilation of a continuous chain of motor automatisms. Here it is appropriate to quote the words of K. Marx: “Human action differs from the work of the“ best bee ”in that, before building, a person has already built in his head. At the end of the labor process, a result is obtained that already before the beginning of this process was ideally available, that is, in the employee's mind ”.
Due to the violation of the plan of action, when trying to complete the task, the patient makes many unnecessary movements. In some cases, parapraxia is observed when an action is performed that only vaguely resembles the given task. Sometimes there are also perseverations, that is, getting stuck on any actions. For example, a patient is asked to make a beckoning hand motion. After completing this task, they offer to shake a finger, but the patient still performs the first action.
In some cases, with apraxia, ordinary, everyday actions are preserved, but professional skills are lost (for example, the ability to use a plane, a screwdriver, etc.).
According to clinical manifestations, there are several types of apraxia: motor, ideator and constructive.
Motor apraxia. The patient cannot perform actions on a task and even on imitation. He is asked to cut the paper with scissors, lace up a shoe, line the paper with a pencil and a ruler, etc., but the patient, although he understands the task, cannot complete it, showing complete helplessness. Even if you show how this is done, the patient still cannot repeat the movement. In some cases, it turns out to be impossible to perform such simple actions as squatting, turning, clapping your hands.
Ideatorial apraxia. The patient cannot perform actions on the assignment with real and imaginary objects (for example, to show how they comb their hair, stir the sugar in a glass, etc.), at the same time, the actions to imitate are saved. In some cases, the patient can automatically, without hesitation, perform certain actions. For example, on purpose, he cannot fasten a button, but performs this action automatically.
Constructive apraxia. The patient can perform various actions by imitation and by verbal order, but is unable to create a qualitatively new motor act, to put together a whole from parts, for example, to make a certain figure out of matches, to fold a pyramid, etc.
Some variants of apraxia are associated with a violation of gnosis. The patient does not recognize the object or his body scheme is disturbed, therefore he is not able to perform tasks or performs them uncertainly and not quite correctly.
For the study of praxis, a number of tasks are offered (sit down, shake your finger, comb your hair, etc.). They also present tasks for actions with imaginary objects (they are asked to show how they eat, how they call on the phone, how they saw wood, etc.). Evaluate how the patient can mimic the displayed actions.
For the study of gnosis and praxis, special psychological techniques are also used. Among them, an important place is occupied by Séguin boards with depressions of various shapes, into which figures corresponding to the depressions must be inserted. This method allows you to assess the degree of mental development. The Koss method is also used: a set of cubes of different colors. From these cubes, you need to add a pattern that matches the one shown in the picture. Older children are also offered a Link's cube: you need to fold a cube out of 27 differently colored cubes so that all its sides are the same color. The patient is shown the assembled cube, then they destroy it and ask to fold it again.
In these techniques, how the child performs the task is of great importance: whether he acts according to the trial and error method or according to a specific plan.
Rice. 56. Scheme of connections of speech centers and regulation of speech activity.
1 - letter center; 2 - Broca's center; 3 - center of praxis; 4 - center of proprioceptive gnosis; 5 - reading center; 6 - center of Wernicke; 7 - the center of auditory gnosis; 8 - the center of visual gnosis.
It is important to remember that praxis is formed as the child matures, so young children cannot yet perform such simple actions as combing, buttoning, etc. Apraxia in their classical form, like agnosia, is found mainly in adults.
Speech and its violations. V the implementation of the speech function, as well as writing and reading, involves visual, auditory, motor and kinesthetic analyzers. Of great importance are the safety of the innervation of the muscles of the tongue, larynx, soft palate, the condition of the paranasal sinuses and the oral cavity, which play the role of resonator cavities. In addition, coordination of breathing and pronunciation of sounds is important.
For normal speech activity, the coordinated functioning of the entire brain and other parts of the nervous system is necessary. Speech mechanisms have a complex and multistage organization (Fig. 56).
Speech is the most important function of a person, therefore, cortical speech zones located in the dominant hemisphere (Broca's and Wernicke's centers), motor, kinetic, auditory and visual areas, as well as conducting afferent and efferent pathways related to the pyramidal and extrapyramidal systems, take part in its implementation. , analyzers of sensitivity, hearing, vision, bulbar parts of the brain, visual, oculomotor, facial, auditory, glossopharyngeal, vagus and hypoglossal nerves.
The complexity, multistage nature of speech mechanisms also determines the variety of speech disorders. If the innervation of the speech apparatus is disturbed, dysarthria- violation of articulation, which can be caused by central or peripheral paralysis of the speech motor apparatus, damage to the cerebellum, striopallidal system.
Distinguish also dislalia- phonetically incorrect pronunciation of certain sounds. Dislalia can be of a functional nature and is quite successfully eliminated during speech therapy classes. Under alalia understand speech retardation. Usually to VA At the age of years the child begins to speak, but sometimes this happens much later, although the child understands well the speech addressed to him. Delayed speech development also affects mental development, since speech is the most important means of information for a child. However, there are also cases of alalia associated with dementia. The child lags behind in mental development, and therefore his speech is not formed. These different cases of alalia need to be differentiated as they have a different prognosis.
With the development of speech function in the dominant hemisphere (for right-handers - in the left, for left-handers - in the right), gnostic and practical speech centers are formed, and subsequently - the centers of writing and reading.
Cortical speech disorders are variants of agnosia and apraxia. Distinguish between expressive (motor) and impressive (sensory) speech. Cortical impairment of motor speech is speech apraxia, sensory speech - speech agnosia. In some cases, the recollection of the necessary words is impaired, that is, the memory mechanisms suffer. Speech agnosias and apraxias are called aphasias.
It should be remembered that speech disorders can be the result of general apraxia (apraxia of the trunk, limbs) or oral apraxia, in which the patient loses the skill to open his mouth, puff out his cheeks, and stick out his tongue. These cases do not apply to aphasias; speech apraxia arises here a second time as a manifestation of general praxical disorders.
Speech disorders in childhood, depending on the causes of their occurrence, can be divided into the following groups:
I. Speech disorders associated with organic damage to the central nervous system. Depending on the level of damage to the speech system, they are divided into:
1) aphasia - the decay of all components of speech as a result of damage to the cortical speech zones;
2) alalia - systemic speech underdevelopment due to lesions of cortical speech zones in the pre-speech period;
3) dysarthria - a violation of the sound-pronunciation side of speech as a result of a violation of the innervation of the speech muscles.
Depending on the localization of the lesion, several forms of dysarthria are distinguished.
II. Speech disorders associated with functional changes
central nervous system:
1) stuttering;
2) mutism and deaf-mutism.
III. Speech disorders associated with defects in the structure of the articulatory apparatus (mechanical dyslalia, rhinolalia).
IV. Delays in speech development of various origins (with prematurity, somatic weakness, pedagogical neglect, etc.).
Sensory aphasia(Wernicke's aphasia), or verbal "deafness", occurs when the left temporal region (middle and posterior parts of the superior temporal gyrus) is affected. A.R. Luria distinguishes two forms of sensory aphasia: acoustic-gnostic and acoustic-mnestic.
The basis of the defect in acoustic-gnostic form constitutes a violation of auditory gnosis. The patient does not differentiate sounding phonemes by ear in the absence of deafness (phonemic analysis is considered), as a result of which the understanding of the meaning of individual words and sentences is distorted and impaired. The severity of these violations can be different. In the most severe cases, the addressed speech is not perceived at all and seems to be speech in a foreign language. This form occurs when the posterior part of the superior temporal gyrus of the left hemisphere is affected - Brodmann's field 22.
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