Localization of functions in the cerebral cortex
General characteristics. In certain areas of the cerebral cortex, neurons are predominantly concentrated that perceive one type of stimulus: the occipital region - light, the temporal lobe - sound, etc. However, after the removal of the classical projection zones (auditory, visual), conditioned reflexes to the corresponding stimuli are partially preserved. According to the theory of I.P. Pavlov, in the cerebral cortex there is a “core” of the analyzer (cortical end) and “scattered” neurons throughout the cortex. The modern concept of function localization 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 (O.S. Adrianov). The degree of multifunctionality of different cortical structures varies. In the fields of the associative cortex, it is higher. The multifunctionality is based on the multichannel input of afferent excitation into the cerebral cortex, the overlap of afferent excitations, especially at the thalamic and cortical levels, the modulating influence of various structures, for example, nonspecific nuclei of the thalamus, basal ganglia, on cortical functions, the interaction of cortical-subcortical and intercortical pathways for conducting excitation. With the help of microelectrode technology, it was possible to register in various areas of the cerebral cortex the activity of specific neurons that respond to stimuli of only one type of stimulus (only to light, only to sound, etc.), i.e. there is a multiple representation of functions in the cerebral cortex .
At present, the division of the cortex into sensory, motor and associative (non-specific) zones (areas) is accepted.
Sensory areas of the cortex. Sensory information enters the projection cortex, the cortical sections of the analyzers (I.P. Pavlov). These zones are located mainly in the parietal, temporal and occipital lobes. The ascending pathways to the sensory cortex come mainly from the relay sensory nuclei of the thalamus.
Primary sensory areas - these are zones of the sensory cortex, irritation or destruction of which causes clear and permanent changes in the sensitivity of the body (the core of the analyzers according to I.P. Pavlov). They consist of monomodal neurons and form sensations of the same quality. Primary sensory areas usually have a clear spatial (topographic) representation of body parts, their receptor fields.
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 part of these neurons has the highest specificity. 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, others - to the nature of the lines (edge, stripe, slope of the line), etc. However, it should be noted that the primary zones of certain areas of the cortex also include multimodal neurons that respond to several types of stimuli. In addition, there are neurons there, the reaction of which reflects the impact of non-specific (limbic-reticular, or modulating) systems.
Secondary sensory areas located around the primary sensory areas, 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 its corresponding part of the paracentral lobule on the medial surface of the hemispheres. This zone is referred to as somatosensory areaI. Here there is a projection of 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. Scheme of sensitive and motor homunculi
(according to W. Penfield, T. Rasmussen). Section of the hemispheres in the frontal plane:
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 somatosensory area I, there are somatosensory area II smaller, located on the border of the intersection of the central sulcus with the upper edge temporal lobe, deep in the lateral groove. The accuracy of localization of body parts is expressed to a lesser extent here. A well-studied primary projection zone is auditory cortex(fields 41, 42), which is located in the depth of the lateral sulcus (the 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.
AT occipital lobe situated primary visual area(cortex of part of the sphenoid gyrus and lingular lobule, field 17). There is a topical representation of retinal receptors here. Each point of the retina corresponds to its own area of the visual cortex, while the zone of the macula has a relatively large zone of representation. In connection with the incomplete decussation of the visual pathways, the same halves of the retina are projected into the visual region 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 arise.
In the secondary zones, the leading ones are the 2nd and 3rd layers of neurons, for which the main part of the information about the environment and the internal environment of the body, received by the sensory cortex, is transmitted for further processing to the associative cortex, after which it is initiated (if necessary) behavioral response with the obligatory participation of the motor cortex.
motor areas of the cortex. Distinguish between primary and secondary motor areas.
AT primary motor area (precentral gyrus, field 4) there are neurons that innervate the motor neurons of the muscles of the face, trunk and limbs. It has a clear topographic projection of the muscles of the body (see Fig. 2). The main pattern of topographic representation is that the regulation of the activity of muscles that provide the most accurate and diverse 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 of the opposite side of the body (for the muscles of the head, the 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). In functional terms, the secondary motor cortex is of paramount importance in relation to the primary motor cortex, carrying out higher motor functions associated with planning and coordinating voluntary movements. Here, the slowly increasing negative readiness potential, occurring approximately 1 s before the start of movement. The cortex of field 6 receives the bulk of the impulses from the basal ganglia and the cerebellum, and is involved in recoding information about the plan of complex movements.
Irritation of the cortex of field 6 causes complex coordinated movements, such as turning the head, eyes and torso in the opposite direction, friendly contractions of the flexors or extensors on the opposite side. The premotor cortex contains motor centers associated with human social functions: the center of written speech in the posterior part of the middle frontal gyrus (field 6), the center of Broca's motor speech in the posterior part of the inferior frontal gyrus (field 44), which provide speech praxis, as well as musical motor center (field 45), providing the tone of speech, the ability to sing. Motor cortex neurons receive afferent inputs through the thalamus from muscle, joint, and skin receptors, from the basal ganglia, and the cerebellum. The main efferent output of the motor cortex to the stem and spinal motor centers are the pyramidal cells of layer V. The main lobes of the cerebral cortex are shown in Fig. 3.
Rice. 3. Four main lobes of the cerebral cortex (frontal, temporal, parietal and occipital); side view. They contain the primary motor and sensory areas, higher-order motor and sensory areas (second, third, etc.) and the associative (non-specific) cortex
Association areas of the cortex(nonspecific, intersensory, interanalyzer cortex) include areas of the new cerebral cortex, which are located around the projection zones and next to the motor zones, but do not directly perform sensory or motor functions, therefore they cannot be attributed primarily to sensory or motor functions, the neurons of these zones have large learning abilities. The boundaries of these areas are not clearly marked. The associative cortex is phylogenetically the youngest part of the neocortex, which has received the greatest development in primates and in 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 motor zones and at the same time serve as a substrate for higher mental functions. Main association areas of the cortex are: parietal-temporal-occipital, prefrontal cortex of the frontal lobes and limbic association zone.
The neurons of the associative cortex are polysensory (polymodal): they respond, as a rule, not to one (like the neurons of the primary sensory zones), but to several stimuli, i.e., the same neuron can be excited when stimulated by auditory, visual, skin and other receptors. Polysensory neurons of the associative cortex are created by cortico-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 excitations and is involved in the integration of sensory information and in ensuring the interaction of sensory and motor areas of the cortex.
Associative areas occupy the 2nd and 3rd cell layers of the associative cortex, where powerful unimodal, multimodal, and nonspecific afferent flows 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 postsynaptic neuron as a condition for synaptic modification, since not all synaptic activity leads to excitation of a postsynaptic neuron. On the basis of D. Hebb's hypothesis, it can be assumed that individual neurons of the associative zones of the cortex are connected in various ways and form cell ensembles that distinguish "subimages", i.e. corresponding to unitary forms of perception. These connections, as noted by D. Hebb, are so well developed that it is enough to activate one neuron, and the entire ensemble is excited.
The apparatus that acts as a regulator of the level of wakefulness, as well as selective modulation and actualization of 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 nervous formations of this apparatus include the limbic and nonspecific systems of the brain with activating and inactivating structures. Among the activating formations, first of all, the reticular formation of the midbrain, the posterior hypothalamus, and the blue spot in the lower parts of the brain stem are distinguished. The inactivating structures include the preoptic area of the hypothalamus, the raphe nucleus in the brainstem, and the frontal cortex.
Currently, according to thalamocortical projections, it is proposed to distinguish three main associative systems of the brain: thalamo-temporal, thalamolobic and thalamic temporal.
thalamotenal system It is represented by associative zones of the parietal cortex, which receive 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 nuclei of the extrapyramidal system. The main functions of the thalamo-temporal system are gnosis and praxis. Under gnosis understand the function of various types of recognition: shapes, sizes, meanings of objects, understanding of speech, knowledge of processes, patterns, etc. Gnostic functions include the assessment of spatial relationships, for example, the relative position of objects. In the parietal cortex, a 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.
Thalamolobic system It is represented by 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 region plays a major role in the development of a behavioral strategy. The violation of this function is especially noticeable when it is necessary to quickly change the action and when some time elapses between the formulation of the problem and the beginning of its solution, i.e. stimuli that require correct inclusion in a holistic behavioral response have time to accumulate.
The thalamotemporal system. Some associative centers, for example, stereognosis, praxis, also include areas of the temporal cortex. The auditory center of Wernicke's speech is located in the temporal cortex, located in the posterior regions 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 center for recognizing musical sounds and their combinations. On the border of the temporal, parietal and occipital lobes there is a reading center that provides recognition and storage of images.
An essential role in the formation of behavioral acts is played by the biological quality of the 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 a person form the basis of his subjective experiences - pleasure and displeasure, joy and sadness. In all cases, goal-directed behavior is built in accordance with the emotional state that arose under the action of a stimulus. During behavioral reactions of a negative nature, the tension of the vegetative 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 (vegetative neuroses).
In this part of the book, the main general questions of the analytical and synthetic activity of the brain are considered, which will make it possible to proceed in subsequent chapters to the presentation of particular questions of the physiology of sensory systems and higher nervous activity.
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This question is extremely important theoretically and especially practically. Hippocrates already knew that brain injuries lead to paralysis and convulsions on the opposite side of the body, and sometimes are accompanied by loss of speech.
In 1861, the French anatomist and surgeon Broca, on autopsy of the corpses of several patients suffering from a speech disorder in the form of motor aphasia, discovered profound changes in the pars opercularis of the third frontal gyrus of the left hemisphere or in the white matter under this area of the cortex. Based on his observations, Broca established in the cerebral cortex the motor center of speech, later named after him.
The English neuropathologist Jackson (1864) spoke in favor of the functional specialization of individual sections of the hemispheres on the basis of clinical data. Somewhat later (1870), the German researchers Fritsch and Gitzig proved the existence of special areas in the dog's cerebral cortex, the stimulation of which by a weak electric current is accompanied by a contraction of individual muscle groups. This discovery caused a large number of experiments, basically confirming the existence of certain motor and sensory areas in the cerebral cortex of higher animals and humans.
On the issue of localization (representation) of function in the cerebral cortex, two diametrically opposed points of view competed with each other: localizationists and antilocalizationists (equipotentialists).
Localizationists were supporters of narrow localization of various functions, both simple and complex.
The anti-localizationists took a completely different view. They denied any localization of functions in the brain. The whole bark for them was equivalent and homogeneous. All its structures, they believed, have the same possibilities for performing various functions (equipotential).
The problem of localization can be correctly resolved only with a dialectical approach to it, which takes into account both the integral activity of the entire brain and the different physiological significance of its individual parts. It was in this way that IP Pavlov approached the problem of localization. In favor of the localization of functions in the cortex, numerous experiments by IP Pavlov and his colleagues with the extirpation of certain areas of the brain convincingly speak. Resection of the occipital lobes of the cerebral hemispheres (centers of vision) in a dog causes enormous damage to the conditioned reflexes developed in it to visual signals and leaves intact all conditioned reflexes to sound, tactile, olfactory and other stimuli. On the contrary, resection of the temporal lobes (hearing centers) leads to the disappearance of conditioned reflexes to sound signals and does not affect the reflexes associated with optical signals, etc. Against equipotentialism, in favor of the representation of the function in certain areas of the cerebral hemispheres, the latest data from electroencephalography also speak . Irritation of a certain area of the body leads to the appearance of reactive (evoked) potentials in the cortex in the "center" of this area.
IP Pavlov was a staunch supporter of localization of functions in the cerebral cortex, but only relative and dynamic localization. The relativity of localization is manifested in the fact that each section of the cerebral cortex, being the carrier of a certain special function, the "center" of this function, responsible for it, participates in many other functions of the cortex, but not as the main link, not in the role of the "center ”, but on a par with many other areas.
The functional plasticity of the cortex, its ability to restore the lost function by establishing new combinations speak not only of the relativity of the localization of functions, but also of its dynamism.
The basis of any more or less complex function is the coordinated activity of many areas of the cerebral cortex, but each of these areas participates in this function in its own way.
The basis of modern ideas about the "systemic localization of functions" is the teaching of I. P. Pavlov about the dynamic stereotype. Thus, the higher mental functions (speech, writing, reading, counting, gnosis, praxis) have a complex organization. They are never carried out by some isolated centers, but are always processes "placed in a complex system of zones of the cerebral cortex" (AR Luria, 1969). These "functional systems" are mobile; in other words, the system of means by which this or that task can be solved changes, which, of course, does not reduce the importance for them of the well-studied “fixed” cortical areas of Broca, Wernicke, and others.
The centers of the cerebral cortex of a person are divided into symmetrical, presented in both hemispheres, and asymmetric, present in only one hemisphere. The latter include the centers of speech and functions associated with the act of speech (writing, reading, etc.), which exist only in one hemisphere: in the left - in right-handers, in the right - in left-handers.
Modern ideas about the structural and functional organization of the cerebral cortex come from the classical Pavlovian concept of analyzers, refined and supplemented by subsequent studies. There are three types of cortical fields (G. I. Polyakov, 1969). The primary fields (analyzer cores) correspond to the architectonic zones of the cortex, where sensory pathways end (projection zones). Secondary fields (peripheral sections of the analyzer nuclei) are located around the primary fields. These zones are connected with receptors indirectly, in them a more detailed processing of incoming signals takes place. Tertiary, or associative, fields are located in zones of mutual overlap of the cortical systems of analyzers and occupy more than half of the entire surface of the cortex in humans. In these zones, inter-analyzer connections are established that provide a generalized form of a generalized action (V. M. Smirnov, 1972). The defeat of these zones is accompanied by violations of gnosis, praxis, speech, purposeful behavior.
At present, it is customary to divide the bark into sensory, motor, or motor, and association areas. Such a division was obtained through animal experiments with the removal of various parts of the cortex, observations of patients with a pathological focus in the brain, as well as with the help of direct electrical stimulation of the cortex and peripheral structures by recording electrical activity in the cortex.
The cortical ends of all analyzers are represented in the sensory zones. For visual it is located in the occipital lobe of the brain (fields 17, 18, 19). In field 17, the central visual pathway ends, informing about the presence and intensity of the visual signal. Fields 18 and 19 analyze the color, shape, size and quality of the item. If field 18 is affected, the patient sees, but does not recognize the object and does not distinguish its color (visual agnosia).
Cortical end auditory analyzer localized in the temporal lobe of the cortex (Geshl's gyrus), fields 41, 42, 22. They are involved in the perception and analysis of auditory stimuli, the organization of auditory control of speech. A patient with damage to field 22 loses the ability to understand the meaning of spoken words.
The cortical end is also located in the temporal lobe leadbular analyzer.
Skin analyzer, as well as pain and temperatureChuvvalidity are projected onto the posterior central gyrus, in the upper part of which the lower limbs are represented, in the middle part - the torso, in the lower part - the arms and head.
Paths end in the parietal cortex somatic feelingrelated to speech functions, associated with the assessment of the impact on the skin receptors, the weight and properties of the surface, the shape and size of the object.
The cortical end of the olfactory and gustatory analyzers is located in the hippocampal gyrus. When this area is irritated, olfactory hallucinations occur, and damage to it leads to anosmia(loss of the ability to smell).
motor zones located in the frontal lobes in the region of the anterior central gyrus of the brain, the irritation of which causes a motor reaction. The cortex of the precentral gyrus (field 4) represents the primary motor zone. In the fifth layer of this field are very large pyramidal cells (giant Betz cells). The face is projected onto the lower third of the precentral gyrus, the hand occupies its middle third, the trunk and pelvis - the upper third of the gyrus. The motor cortex for the lower extremities is located on the medial surface of the hemisphere in the region of the anterior part of the paracentral lobule.
The premotor area of the cortex (field 6) is located anterior to the primary motor area. Field 6 is called secondary mothorny area. Her irritation causes rotation of the trunk and eyes with the raising of the contralateral arm. Similar movements are observed in patients during an epileptic attack, if the epileptic focus is localized in this area. Recently, the leading role of field 6 in the implementation of motor functions has been proven. The defeat of field 6 in a person causes a sharp restriction of motor activity, complex sets of movements are difficult to perform, spontaneous speech suffers.
Field 6 is adjacent to field 8 (frontal oculomotor), the irritation of which is accompanied by a turn of the head and eyes in the opposite direction to the irritated one. Stimulation of different parts of the motor cortex causes contraction of the corresponding muscles on the opposite side.
Anterior frontal cortex associated with creative thinking. From a clinical and functional point of view, the region of interest is the inferior frontal gyrus (field 44). In the left hemisphere, it is associated with the organization of the motor mechanisms of speech. Irritation of this area can cause vocalization, but not articulate speech, as well as cessation of speech if the person has spoken. The defeat of this area leads to motor aphasia - the patient understands speech, but he cannot speak.
The association cortex includes the parietal-temporal-occipital, prefrontal, and limbic regions. It occupies about 80% of the entire surface of the cerebral cortex. Its neurons have multisensory functions. In the associative cortex, various sensory information is integrated and a program of purposeful behavior is formed, the associative cortex surrounds each projection zone, providing a relationship, for example, between sensory and motor areas of the cortex. The neurons located in these areas have polysensory, those. the ability to respond to both sensory and motor input.
Parietal association area the cerebral cortex is involved in the formation of a subjective idea of the surrounding space, of our body.
Temporal cortex participates in speech function through auditory control of speech. With the defeat of the auditory center of speech, the patient can speak, correctly express his thoughts, but does not understand someone else's speech (sensory auditory aphasia). This area of the cortex plays a role in the evaluation of space. The defeat of the visual center of speech leads to the loss of the ability to read and write. The function of memory and dreams is associated with the temporal cortex.
Frontal association fields are directly related to the limbic parts of the brain, they take part in the formation of a program of complex behavioral acts in response to the influence of the external environment based on sensory signals of all modalities.
A feature of the associative cortex is the plasticity of neurons capable of restructuring depending on the incoming information. After an operation to remove any area of the cortex in early childhood, the lost functions of this area are completely restored.
The cerebral cortex is capable, in contrast to the underlying structures of the brain, for a long time, throughout life, to preserve traces of incoming information, i.e. participate in the mechanisms of long-term memory.
The cerebral cortex is a regulator of the autonomic functions of the body (“corticolization of functions”). It presents all unconditioned reflexes, as well as internal organs. Without the cortex, it is impossible to develop conditioned reflexes to internal organs. When stimulating interoreceptors by the method of evoked potentials, electrical stimulation and destruction of certain areas of the cortex, its effect on the activity of various organs has been proven. Thus, the destruction of the cingulate gyrus changes the act of breathing, the functions of the cardiovascular system, and the gastrointestinal tract. The bark inhibits emotions - "know how to rule yourself."
The cerebral cortex is the evolutionarily youngest formation that has reached the largest values in humans in relation to the rest of the brain mass. In humans, the mass of the cerebral cortex is on average 78% of the total mass of the brain. The cerebral cortex is extremely important in the regulation of the vital activity of the organism, the implementation of complex forms of behavior and in the development 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 department can function normally only in close interaction with subcortical formations. The contrast between the cortex and the underlying parts of the brain is largely schematic and conditional. In recent years, ideas have been developed about the vertical organization of the functions of the nervous system, about circular cortical-subcortical connections.
The cells of the cortical substance are specialized to a much lesser extent 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 fairly significant areas of the cortical substance can be clinically very blurred (the so-called clinical silent zones). The absence of a narrow specialization of cortical neurons creates the 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 basis for the ability to learn. The theoretically possible number of connections between the 14 billion cells of the cerebral cortex is so great that during a person's life a significant part of them remains unused. This once again confirms the unlimited possibilities of human learning.
Despite the well-known non-specificity 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 speak of 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 centers of will, thinking, the ability to understand art, etc. At present, it would be wrong 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 I.P. Pavlov, the brain center, or the cortical section of the analyzer, consists of a “core” and “scattered elements”. The "nucleus" is a relatively morphologically homogeneous group of cells with an accurate projection of receptor fields. "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 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 (layer IV) and with muscles (layer V) 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 predominate, therefore they are also called projection-associative.
In the cortical representations of the analyzers, thus, 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, where the auditory pathways end, in the posterior central gyrus - the cortical section 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 stimulation of the cortex showed that excitation of the primary zones of the sensory regions leads to the emergence of elementary sensations. For example, irritation of the occipital regions causes a sensation of flashing points of light, dashes, etc. When the 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 are distinguished in the cortical substance, or zones of overlap of the cortical representations of individual analyzers. In humans, they occupy a very significant place and are located primarily in the parietal-temporal-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 occupy the first place in humans. In the tertiary zones, therefore, operations of planning and control 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 does a constant concentration of functional zones occur in outlined centers separated from each other. In the clinic, in adult patients, very constant symptom complexes are observed when certain areas of the cortical substance and the nerve pathways associated with them are affected.
In childhood, due to incomplete differentiation of functional areas, 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.
Functionally, the main integrative levels of cortical activity can be distinguished.
The first signaling system is associated with the activities of individual analyzers and carries out the primary stages of gnosis and praxis, i.e., the integration of signals coming through the channels of individual analyzers and the formation of response actions, taking into account the state of the external and internal environment, as well as past experience. This first level includes visual perception of objects with a concentration of attention on certain details of it, voluntary movements with active amplification or inhibition of them.
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 world around us “with knowledge and understanding.” This level of integration is closely connected with the speech activities, and the understanding of speech (speech gnosis) and the use of speech as a means of communication and thinking (speech praxis) are not only interconnected, 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" the signals that are of the greatest importance at the moment, from secondary signals, the implementation of probabilistic forecasting of the future and the formation of promising tasks.
Of course, complex cortical activity could not be carried out without the participation of the 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 essential, but also the functions of obtaining the necessary information from memory “stores” (recollection), as well as the functions of transferring information flows from RAM blocks (what is needed at the moment) to blocks of long-term memory and vice versa. Otherwise, the assimilation of the new would be impossible, since the old skills and knowledge would interfere with this.
Recent neurophysiological studies have made it possible to establish which functions are predominantly characteristic of certain sections 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 (Geshl's convolutions), the taste analyzer, the anterior central gyrus with the motor, the posterior central gyrus with the musculoskeletal 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-practical functions, the cortical regions lying in the parietal-temporal-occipital region take an active part. The defeat of these areas leads to more complex forms of disorders. The gnostic speech center of Wernicke is located in the temporal lobe of the left hemisphere. The motor center of speech is located somewhat anterior to the lower third of the anterior central gyrus (Broc's center). In addition to the centers of oral speech, there are sensory and motor centers of written speech and a number of other formations, one way or another connected with speech. The parietal-temporal-occipital region, where the paths coming from various analyzers are closed, is of great importance for the formation of higher mental functions. The well-known 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 area. According to modern concepts, it is this section 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 stimuli coming from skeletal muscles, tendons, joints and bones. In the V and partly VI layer there are Betz's giant pyramidal cells, the fibers of which form the pyramidal pathway. The anterior central gyrus has a certain somatotopic projection and is associated with the opposite half of the body. In the upper sections of the gyrus, the muscles of the lower extremities are projected, in the lower - of the face. The trunk, larynx, pharynx are presented 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, the vestibular nuclei, formations of the striopallidar system involved in the regulation of torsion, as well as with the cortical section of the visual analyzer (field 17).
In the posterior sections of the superior frontal gyrus, a center is present that gives rise to the fronto-cerebellopontine pathway (field 8). This area of the cerebral cortex is involved in ensuring the coordination of movements associated with bipedalism, 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 back 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 posterior to it by the lower section of the anterior central gyrus (the projection zone of the lips, tongue and larynx) and to the anterior musical motor center.
The musical motor center (field 45) provides a certain tonality, modulation of speech, 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 close proximity to the projection cortical zone of the hand (field 6). The center provides automatism of writing and is functionally connected with 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 upper parietal region (fields 5 and 7). Tactile, pain, temperature sensitivity of the opposite half of the body is projected in the posterior central gyrus. In the upper sections, the sensitivity of the leg is projected, in the lower sections - the sensitivity of the face. Boxes 5 and 7 represent elements of deep sensitivity. 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.
Behind the upper sections of the posterior central gyrus, there is a center that 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 lower parietal lobule on the left, supramarginal gyrus (fields 40 and 39). The center ensures the storage and implementation of images of motor automatisms (praxis functions).
In the lower sections of the anterior and posterior central gyri, there is a center for the analyzer of interoceptive impulses of internal organs and blood vessels. The center has close ties with subcortical vegetative formations.
The temporal share. The center of the auditory analyzer is located in the middle part of the superior temporal gyrus, on the surface facing the insula (Geshl's 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 sections of the outer surface of the temporal lobe, is projective, is in close connection with the lower basal sections of the temporal lobes, giving rise to the occipital-temporal cortical-pontocerebellar tract.
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 zone of sensitivity; IV - projection visual zone; projection gnostic zones: V - hearing; VI - smell, VII - taste, VIII - gnostic zone of the body scheme; IX - zone of stereognosis; X - gnostic visual zone; XI - Gnostic reading zone; XII - Gnostic speech zone; XIII - praxis zone; XIV - praxic speech zone; XV - praxic zone of writing; 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 the ammon horn (field 11a, e) and provides the projection function, as well as the storage and recognition of olfactory images.
The center of the taste analyzer is located in the immediate vicinity of the center of the olfactory analyzer, i.e., in the hook and ammon horn, 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 a projection function, storage and recognition of taste patterns.
The acoustic-gnostic sensory center of speech (Wernicke's center) is localized in the posterior sections of the superior temporal gyrus on the left, in the depth of the lateral sulcus (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 Wernicke's center (the 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 zone, fields 18 and 19 provide storage and recognition of visual images, visual orientation in an unusual 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's center of the temporal lobe, with the center of the visual analyzer of the occipital lobe, and also with the centers of the parietal lobe. The Reading Center provides recognition and storage of images of written speech.
Data on the localization of functions were obtained either as a result of stimulation of various sections of the cortex in the experiment, or as a result of an analysis of disturbances resulting from damage to certain areas 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, unambiguous connection with strictly defined functions.
In the 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, phenomena of delayed or disturbed development of cortical functions are observed in childhood, which largely modifies the "classic" symptoms. The existence of different functional types of cortical activity causes different symptoms of cortical lesions. Analysis of these symptoms 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 violations of gnosis and praxis at different levels of integration; speech disorders due to their practical importance; disorders of regulation of purposefulness, purposefulness of neurophysiological functions. With each type of disorder, the mechanisms of memory involved in this functional system can also be disturbed. In addition, more total memory impairments are possible. In addition to relatively local cortical symptoms, more diffuse symptoms are also observed in the clinic, manifested primarily in intellectual insufficiency and 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, to maintain a relaxed tone of conversation with him. Since many of the diagnostic tasks presented to the child are very complex, it is necessary to strive so that he not only understands the task, but also becomes interested in it. Sometimes, when examining excessively distracted, motor-disinhibited, or mentally retarded children, much patience and ingenuity must be applied in order to identify the existing deviations. In many cases, the analysis of the child's cortical functions is aided by reports from parents 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 purposeful tasks. Separate psychological techniques make it possible to evaluate certain aspects of mental activity in isolation, others more comprehensively. These include the so-called personality tests.
Gnosis and its disorders. Gnosis literally means recognition. Our orientation in the surrounding world is connected with the recognition of the shape, size, spatial correlation of objects and, finally, with the understanding of their meaning, which is contained in the name of the object. This stock of information about the surrounding world is made up of the analysis and synthesis of sensory impulse flows and is deposited in memory systems. The receptor apparatus and the transmission of sensory impulses are preserved in the case of lesions of higher gnostic mechanisms, but the interpretation of these impulses, the comparison of the received data with the images stored in the memory, are violated. As a result, a disorder of gnosis arises - 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 detail, becomes alien, incomprehensible, devoid of meaning.
But gnosis cannot be imagined as a simple juxtaposition, recognition of an image. Gnosis is a process of continuous renewal, clarification, concretization of the image stored in the memory matrix, under the influence of its re-comparison with the received information.
total agnosia, in which there is complete disorientation, occurs infrequently. Significantly more often, gnosis is disturbed in any one analyzer system, and, depending on the degree of damage, the severity of agnosia is different.
Visual agnosia occur with damage to the occipital cortex. 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 his hands, then he will recognize it when he feels it. There are times when the patient does not recognize familiar faces. Some patients with a similar disorder are forced to remember people according to some other signs (clothing, mole, etc.). In other cases, the patient with agnosia recognizes an 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 disturbed. In practice, even when an object is not recognized, one can speak of violations of the mechanisms of memory, since the perceived object cannot be compared with its image in the gnostic matrix. But there are also cases when, upon repeated presentation of an object, the patient says that he has already seen it, although he still cannot recognize it. With violations of the spatial orientation of the patient, not only does he not recognize the faces, houses, etc. familiar to him before, but he can walk many times in the same place without suspecting it.
Often, with visual agnosia, 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 subject, they are asked to determine, describe their appearance, compare which objects are larger, which are smaller. A set of pictures is also used, color, monochrome and contour. Evaluate not only the recognition of objects, faces, but also plots. Along the way, you can also check visual memory: present several pictures, then mix them with previously unseen ones and ask the child to choose familiar pictures. At the same time, work time, perseverance, and fatigue are also taken into account.
It should be borne in mind that children recognize contour pictures worse than color and plain ones. Understanding the plot is related to the age of the child and the degree of mental development. At the same time, classical agnosias in children are rare due to incomplete differentiation of cortical centers.
auditory agnosia. Occur when the temporal lobe is damaged in the region of the Geshl gyrus. The patient cannot recognize previously familiar sounds: the ticking of a clock, the ringing of a bell, the sound of pouring water. There may be violations of recognition of musical melodies - amusia. In some cases, the definition of the direction of sound is violated. In some types of auditory agnosia, the patient is unable to distinguish the frequency of sounds, such as metronome beats.
Sensitive agnosias are caused by impaired recognition of tactile, pain, 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 is also unable to determine the shape of the object, the feature 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 violations of 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 speak of a disorder of the body scheme.
Taste and olfactory agnosia are rare. In addition, the recognition of smells is very individual, largely due to the personal experience of a person.
Praxis and its 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 inalienable human ability as simple movements. But when the cortical mechanisms involved in the implementation of these acts are damaged, peculiar motor disorders arise - apraxia, in which there are no paralysis, no violations of tone or coordination, and even simple voluntary movements are possible, but more complex, purely human motor acts are violated. The patient suddenly finds himself unable to perform such seemingly simple actions as shaking hands, fastening buttons, combing his hair, lighting a match, etc. Apraxia occurs primarily with damage to the parietal-temporal-occipital region of the dominant hemisphere. In this case, both halves of the body are affected. Apraxia can also occur with damage to the subdominant right hemisphere (in right-handed people) 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 start of this process was ideal, that is, in the mind of the worker.
Due to the violation of the action plan, 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 remotely resembles this task. Sometimes there are also perseverations, i.e., getting stuck on any actions. For example, the patient is asked to make an alluring hand movement. After completing this task, they offer to wag a finger, but the patient still performs the first action.
In some cases, with apraxia, ordinary, everyday activities are preserved, but professional skills are lost (for example, the ability to use a planer, screwdriver, etc.).
According to clinical manifestations, several types of apraxia are distinguished: motor, ideational and constructive.
motor apraxia. The patient cannot perform actions on assignment and even on imitation. He is asked to cut the paper with scissors, lace up his shoe, line the paper with a pencil and ruler, etc., but the patient, although he understands the task, cannot complete it, showing complete helplessness. Even if you show how it is done, the patient still cannot repeat the movement. In some cases, it is impossible to perform such simple actions as squatting, turning, clapping.
ideational apraxia. The patient cannot perform actions on the task with real and imaginary objects (for example, show how they comb their hair, stir sugar in a glass, etc.), at the same time, imitation actions are preserved. In some cases, the patient can automatically, without hesitation, perform certain actions. For example, purposefully, 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 put together a pyramid, etc.
Some variants of apraxia are associated with impaired gnosis. The patient does not recognize the subject or his body scheme is disturbed, so he is not able to perform tasks or performs them uncertainly and not quite correctly.
To study praxis, a number of tasks are offered (sit down, wag a finger, comb your hair, etc.). They also present tasks for actions with imaginary objects (they ask to show how they eat, how they call on the phone, how they cut firewood, etc.). Evaluate how the patient can imitate the actions shown.
Special psychological techniques are also used to study gnosis and praxis. Among them, an important place is occupied by Segen boards with recesses of various shapes, in which you need to put figures corresponding to the recesses. This method also allows assessing 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 corresponding to the one shown in the picture. Older children are also offered a Link cube: you need to add a cube from 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 them to fold it again.
In these methods, it is of great importance how the child performs the task: whether he acts according to the trial and error method or according to a certain plan.
Rice. 56. Scheme of connections between speech centers and regulation of speech activity.
1 - the center of the letter; 2 - Broca's center; 3 - center of praxis; 4 - center of proprioceptive gnosis; 5 - reading center; 6 - Wernicke's center; 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 their hair, fastening buttons, etc. Apraxia in their classic form, like agnosia, occurs mainly in adults.
Speech and its disorders. AT the visual, auditory, motor and kinesthetic analyzers take part in the implementation of the speech function, as well as writing and reading. Of great importance are the preservation of the innervation of the muscles of the tongue, larynx, soft palate, the state 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 multi-stage organization (Fig. 56).
Speech is the most important function of a person, therefore, cortical speech zones located in the dominant hemisphere (Brock and Wernicke 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, multi-stage nature of speech mechanisms also determines the diversity of speech disorders. When the innervation of the speech apparatus is disturbed, dysarthria- violation of articulation, which may be due to central or peripheral paralysis of the speech motor apparatus, damage to the cerebellum, striopallidar system.
There are also dyslalia- phonetically incorrect pronunciation of individual sounds. Dyslalia can be functional in nature and is quite successfully eliminated during speech therapy classes. Under alalia understand speech delay. Usually to VA At the age of 18, the child begins to speak, but sometimes this happens much later, although the child understands well the speech addressed to him. The delay in speech development also affects mental development, since speech is the most important means of information for the 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 the 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 - centers of writing and reading.
Cortical speech disorders are variants of agnosia and apraxia. There are expressive (motor) and impressive (sensory) speech. Cortical impairment of motor speech is speech apraxia, sensory speech - speech agnosia. In some cases, the recall of the necessary words is disturbed, i.e., 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 ability to open his mouth, puff out his cheeks, stick out his tongue. These cases do not apply to aphasias; speech apraxia here occurs a second time as a manifestation of general praxic 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 disintegration of all components of speech as a result of damage to the cortical speech zones;
2) alalia - systemic underdevelopment of speech due to lesions of the cortical speech zones in the pre-speech period;
3) dysarthria - a violation of the sound-producing 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 deafness.
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 is affected (middle and posterior sections of the superior temporal gyrus). A. R. Luria distinguishes two forms of sensory aphasia: acoustic-gnostic and acoustic-mnestic.
The basis of the defect acoustic-gnostic form constitutes a violation of auditory gnosis. The patient does not differentiate by ear phonemes similar in sound 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 disrupted. The severity of these disorders may vary. In the most severe cases, the addressed speech is not perceived at all and seems to be a speech in a foreign language. This form occurs when the posterior part of the upper temporal gyrus of the left hemisphere is damaged - Brodmann's field 22.
Morphological bases of dynamic localization of functions in the cortex of the cerebral hemispheres (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 diagnosing lesions in the cerebral hemispheres.
The idea of the localization of a function in the cerebral cortex is associated primarily with the concept of the cortical center. Back in 1874, the Kievan anatomist V. A. Betz made the statement that each section of the cortex differs in structure from other sections of the brain. This was the beginning of the doctrine of the heterogeneity of the cerebral cortex - cytoarchitectonics (cytos - cell, architectones - system). The studies of Brodman, Economo and employees of the Moscow Institute of the Brain, led by S. A. Sarkisov, managed to identify more than 50 different sections of the cortex - cortical cyto-architectonic fields, each of which differs from the others in the structure and location of nerve elements; there is also a division of the cortex into more than 200 fields. From these fields, designated by numbers, a special “map” of the human cerebral cortex was compiled (Fig. 299).
According to IP Pavlov, the center is the brain end of the so-called analyzer. The analyzer is a nervous mechanism whose function is to decompose the known complexity of the external and internal world into separate elements, i.e., to perform analysis. At the same time, thanks to extensive connections with other analyzers, synthesis also takes place here, a combination of analyzers with each other and with various activities of the organism. "The analyzer is a complex nervous mechanism that begins with an external perceiving apparatus and ends in the brain." From the point of view of I. P. Pavlov, the brain center, or the cortical end of the analyzer, does not have strictly defined boundaries, but consists of a nuclear and diffuse part - the theory of the nucleus and scattered elements. The "nucleus" represents a detailed and accurate projection in the cortex of all elements of the peripheral receptor and is necessary for the implementation of higher analysis and synthesis. "Scattered elements" are located on the periphery of the nucleus and can be scattered far from it; they carry out a simpler and more elementary analysis and synthesis. When the nuclear part is damaged, scattered elements can to a certain extent compensate for the lost function of the nucleus, which is of great clinical importance for the restoration of this function.
Before I.P. Pavlov, the cortex distinguished between the motor zone, or motor centers, the anterior central gyrus and the sensory zone, or sensory centers located behind the sulcus centralis Rolandi. IP Pavlov showed that the so-called motor zone, corresponding to the anterior central gyrus, is, like other zones of the cerebral cortex, a perceiving area (the cortical end of the motor analyzer). "The motor area is the receptor area ... This establishes the unity of the entire cortex of the hemispheres."
At present, the entire cerebral cortex is regarded as a continuous perceiving surface. The cortex is a collection of cortical ends of the analyzers. From this point of view, we will consider the topography of the cortical sections of the analyzers, i.e., the main perceiving areas of the cortex of the cerebral hemispheres.
Let us first consider the cortical ends of internal analyzers.
1. The core of the motor analyzer, i.e., the analyzer of proprioceptive (kinesthetic) stimuli emanating from bones, joints, skeletal muscles and their tendons, is located in the anterior central gyrus (fields 4 and 6) and lobulus paracentralis. Here motor conditioned reflexes are closed. I. P. Pavlov explains motor paralysis that occurs when the motor zone is damaged not by damage to motor efferent neurons, but by a violation of the core of the motor analyzer, as a result of which the cortex does not perceive kinesthetic stimuli and movements become impossible. The cells of the nucleus of the motor analyzer are laid down in the middle layers of the cortex of the motor zone. In its deep layers (5th, partly also 6th) lie Betz's giant pyramidal cells, which are efferent neurons, which I.P. Pavlov considers as intercalary neurons connecting the cerebral cortex with subcortical nodes, nuclei of the head nerves and anterior horns spinal cord, i.e. with motor neurons. In the anterior central gyrus, the human body, as well as in the posterior one, is projected upside down. At the same time, the right motor area is connected with the left half of the body and vice versa, because the pyramidal paths starting from it intersect partly in the medulla oblongata, and partly in the spinal cord. .The muscles of the trunk, larynx, pharynx are under the influence of both hemispheres. In addition to the anterior central gyrus, proprioceptive impulses (muscle-articular sensitivity) also come to the cortex of the posterior central gyrus.
2. The core of the motor analyzer, which is 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 when field 17 is stimulated, located in the occipital lobe in the vicinity of the nucleus of the visual analyzer. Since when the muscles of the eye contract, the cerebral cortex (motor analyzer, field 8) always receives not only impulses from the receptors of these muscles, but also impulses from the retina (visual analyzer, field 17), various visual stimuli are always combined with a different position of the eyes, established contraction of the muscles of the eyeball.
3. The core of the motor analyzer, through which the synthesis of purposeful combined movements takes place, is placed in the left (in right-handers) lower parietal lobule, in the gyrus supramarginalis (deep layers of field 40). These coordinated movements, formed on 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 anterior central gyrus. With the defeat of field 40, the ability to move in general is preserved, but there is an inability to make purposeful movements, to act - apraxia (praxia - action, practice).
4. The core of the analyzer of the position and movement of the head - the static analyzer (vestibular apparatus) - has not yet been exactly localized in the cerebral cortex. There is reason to believe that the vestibular apparatus is projected in the same area of the cortex as the cochlea, i.e., in the temporal lobe. So, with the defeat of fields 21 and 20, which lie in the region of the middle and lower temporal gyri, ataxia is observed, that is, an imbalance, 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 rocket aviation, since the sensitivity of the vestibular apparatus is significantly reduced on an airplane.
5. The core of the analyzer of impulses coming from the viscera and blood vessels (vegetative functions) is located in the lower sections of the anterior and posterior central gyri. Centripetal impulses from the viscera, blood vessels, smooth muscles and glands of the skin enter this section of the cortex, from where the centrifugal paths proceed to the subcortical vegetative centers.
In the premotor region (fields 6 and 8), the vegetative and animal functions are combined. However, it should not be considered that only this area of the cortex affects the activity of the viscera. They are influenced by the state of the entire cerebral cortex.
Nerve impulses from the external environment of the organism 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. Damage leads to cortical deafness.
2. The core of the visual analyzer is located in the occipital lobe - fields 17, 18, 19. On the inner surface of the occipital lobe, along the edges of the sulcus calcarinus, the visual path ends in field 17. The retina is projected here, and the visual analyzer of each hemisphere is associated with the fields of view and the corresponding halves of the retina of both eyes (for example, the left hemisphere is associated with the lateral half of the left eye and the medial right). When the nucleus of the visual analyzer is damaged, blindness occurs. Above field 17 is field 18, in case of damage to which vision is preserved and only visual memory is lost. Even higher is field 19, with the defeat of which one loses orientation in an unusual environment.
3. The nucleus of the olfactory analyzer is located in the phylogenetically most ancient part of the cerebral cortex, within the base of the olfactory brain - uncus, partly Ammon's horn (field 11).
4. According to some data, the core of the taste analyzer is located in the lower part of the posterior central gyrus, close to the centers of the muscles of the mouth and tongue, according to others - in the uncus, in the immediate vicinity of the cortical end of the olfactory analyzer, which explains the close connection between olfactory and taste sensations. It has been established that taste disorder occurs when field 43 is affected.
The analyzers of smell, taste and hearing of each hemisphere are connected with the receptors of the corresponding organs of both sides of the body.
5. The core of the skin analyzer (tactile, pain and temperature sensitivity) is located in the posterior central gyrus (fields 1, 2, 3) and in the cortex of the upper parietal region (fields 5 and 7). In this case, the body is projected in the posterior central gyrus upside down, so that in its upper part there is a projection of the receptors of the lower extremities, and in the lower part - the projection of the receptors of the head. Since in animals the receptors of general sensitivity are especially developed at the head end of the body, in the region of the mouth, which plays a huge role in capturing food, a strong development of the mouth receptors has also been preserved in humans. In this regard, the region of the latter occupies an unreasonably large zone in the cortex of the posterior central gyrus. At the same time, in connection with the development of the hand as a labor organ, the tactile receptors in the skin of the hand increased sharply, which also became the organ of touch. Correspondingly, the areas of the cortex related to the receptors of the upper limb sharply outnumber the region of the lower limb. Therefore, if you draw a figure of a person head down (to the base of the skull) and feet up (to the upper edge of the hemisphere) into the posterior central gyrus, then you need to draw a huge face with an incongruously large mouth, a large hand, especially a hand with a thumb that is sharply superior to the rest, small body and small legs. Each posterior central gyrus is connected to the opposite part of the body due to the intersection of sensory conductors in the spinal cord and a part in the medulla oblongata.
A particular type of skin sensitivity - recognition of objects by touch, stereognosia (stereos - spatial, gnosis - knowledge) - is associated with a section of the cortex of the upper parietal lobule (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 damaged, the ability to recognize objects by touch, with eyes closed, is lost.
The described cortical ends of the analyzers are located in certain areas of the cerebral cortex, which is thus "a grandiose mosaic, a grandiose signaling board." Thanks to the analyzers, signals from the external and internal environment of the body fall onto this “board”. These signals, according to I. P. Pavlov, constitute the first signal system of reality, manifested in the form of concrete visual thinking (sensations and complexes of sensations - perceptions). The first signaling system is also found in animals. But “in the developing animal world, an extraordinary addition to the mechanisms of nervous activity took place in the human phase. For an animal, reality is signaled almost exclusively only by stimuli and their traces in the cerebral hemispheres, which directly arrive at special cells of the visual, auditory, and other receptors of the organism. This is what we also have in ourselves as impressions, sensations and ideas from the external environment, both general natural and from our social, excluding the word, audible and visible. This is the first signaling system we have in common with animals. But the word constituted the second, specially our signal system of reality, being the signal of the first signals... it was the word that made us human.”
Thus, I. P. Pavlov distinguishes between two cortical systems: the first and second signal systems of reality, from which the first signal system first arose (it is also found in animals), and then the second - it is only in humans and is a verbal system. The second signal system is human thinking, which is always verbal, because language is the material shell of thinking. Language is "... the immediate reality of thought."
Through a very long repetition, temporary connections were formed between certain signals (audible sounds and visible signs) and movements of the lips, tongue, muscles of the larynx, on the one hand, and with real stimuli or ideas about them, on the other. Thus, on the basis of the first signal system, the second one arose.
Reflecting this process of phylogenesis, in ontogeny, the first signal system is first laid down in a person, and then the second. In order for the second signaling system to start functioning, the child's communication with other people and the acquisition of oral and written language skills are required, which takes a number of years. If a child is born deaf or loses his hearing before he begins to speak, then his inherent ability to speak is not used and the child remains mute, although he can pronounce sounds. In the same way, if a person is not taught to read and write, then he will forever remain illiterate. All this testifies to the decisive influence of the environment for the development of the second signaling system. The latter is associated with the activity of the entire cerebral cortex, but some areas of it play a special role in the implementation of speech. These areas of the cortex are the nuclei of speech analyzers.
Therefore, in order to understand the anatomical substrate of the second signaling system, in addition to knowing the structure of the cerebral cortex as a whole, it is also necessary to take into account the cortical ends of speech analyzers (Fig. 300).
1. Since speech was a means of communication between people in the course of their joint labor activity, motor analyzers of speech developed in the immediate vicinity of the core of the common motor analyzer.
The motor speech articulation analyzer (motor speech analyzer) is located in the posterior part of the inferior frontal gyrus (gyrus Vgoca, field 44), in close proximity to the lower motor zone. It analyzes the stimuli coming from the muscles involved in the creation of oral speech. This function is associated with the motor analyzer of the muscles of the lips, tongue and larynx, located in the lower part of the anterior central gyrus, which explains the proximity of the speech motor analyzer to the motor analyzer of these muscles. With the defeat of field 44, the ability to produce the simplest movements of the speech muscles, to scream and even sing, remains, but the ability to pronounce words is lost - motor aphasia (phasis - speech). In front of field 44 is field 45 related to speech and singing. When it is defeated, vocal amusia arises - the inability to sing, compose musical phrases, as well as agrammatism - the inability to compose sentences from words.
2. Since the development of oral speech is associated with the organ of hearing, an auditory analyzer of oral speech has developed in close proximity to the sound analyzer. Its nucleus is located in the back of the superior temporal gyrus, deep in the lateral sulcus (field 42, or Wernicke's center). Thanks to the auditory analyzer, various combinations of sounds are perceived by a person as words that mean various objects and phenomena and become their signals (second signals). With the help of it, a person controls his speech and understands someone else's. When it is damaged, the ability to hear sounds is preserved, but the ability to understand words is lost - verbal deafness, or sensory aphasia. When field 22 (the middle third of the superior temporal gyrus) is affected, musical deafness occurs: the patient does not know the motives, and musical sounds are perceived by him as chaotic noise.
3. At a higher stage of development, mankind has learned not only to speak, but also to write. Written speech requires certain hand movements when writing letters or other signs, which is associated with a motor analyzer (general). Therefore, the motor analyzer of written speech is placed in the posterior part of the middle frontal gyrus, near the zone of the anterior central gyrus (motor zone). The activity of this analyzer is connected with the analyzer of the learned hand movements necessary for writing (field 40 in the lower parietal lobule). If field 40 is damaged, all types of movement are preserved, but the ability of subtle movements necessary to draw letters, words and other signs (agraphia) is lost.
4. Since the development of written speech is also connected with the organ of vision, a visual analyzer of written speech has developed in close proximity to the visual analyzer, which, naturally, is connected to the sulcus calcarinus, where the general visual analyzer is located. The visual analyzer of written speech is located in the lower parietal lobule, with gyrus angularis (field 39). If field 39 is damaged, vision is preserved, but the ability to read (alexia) is lost, that is, to analyze written letters and compose words and phrases from them.
All speech analyzers are laid down in both hemispheres, but develop only on one side (in right-handers - on the left, in left-handers - on the right) and functionally turn out to be asymmetric. This connection between the motor analyzer of the hand (organ of labor) and speech analyzers is explained by the close connection between labor and speech, which had a decisive influence on the development of the brain.
"... Labor, and then articulate speech along with it ..." led to the development of the brain. This connection is also used for medicinal purposes. With damage to the speech-motor analyzer, the elementary motor ability of the speech muscles is preserved, but the possibility of oral speech is lost (motor aphasia). In these cases, it is sometimes possible to restore speech by a long exercise of the left hand (in right-handed people), the work of which favors the development of the rudimentary right-hand nucleus of the speech-motor analyzer.
Analyzers of oral and written speech perceive verbal signals (as I. P. Pavlov says - signal signals, or second signals), which constitutes the second signal system of reality, manifested in the form of abstract abstract thinking (general ideas, concepts, conclusions, generalizations), which characteristic only of man. However, the morphological basis of the second signaling system is not only these analyzers. Since the function of speech is phylogenetically the youngest, it is also the least localized. It is inherent in the entire cortex. Since the cortex grows along the periphery, the most superficial layers of the cortex are related to the second signaling system. These layers consist of a large number of nerve cells (100 billion) with short processes, which create the possibility of an unlimited closing function, wide associations, which is the essence of the activity of the second signaling system. At the same time, the second signaling system does not function separately from the first, but in close connection with it, more precisely on the basis of it, since the second signals can arise only in the presence of the first. “The basic laws established in the operation of the first signaling system must also govern the second, because this is the work of the same nervous tissue.”
IP Pavlov's doctrine of two signal systems gives a materialistic explanation of human mental activity and constitutes the natural scientific basis of VI Lenin's theory of reflection. According to this theory, the objective real world, which exists independently of our consciousness, is reflected in our consciousness in the form of subjective images.
Feeling is a subjective image of the objective world.
In the receptor, an external stimulus, such as light energy, is converted into a nervous process, which becomes a sensation in the cerebral cortex.
The same quantity and quality of energy, in this case light, in healthy people will cause a sensation of green color in the cerebral cortex (subjective image), and in a patient with color blindness (due to a different structure of the retina) - a sensation of red color.
Consequently, light energy is an objective reality, and color is a subjective image, its reflection in our consciousness, depending on the structure of the sense organ (eye).
Hence, from the point of view of Lenin's theory of reflection, the brain can be characterized as an organ of reflection of reality.
After all that has been said about the structure of the central nervous system, one can note the human signs of the structure of the brain, that is, the specific features of its structure that distinguish man from animals (Fig. 301, 302).
1. The predominance of the brain over the spinal cord. So, in carnivores (for example, in a cat), the brain is 4 times heavier than the spinal cord, in primates (for example, in a macaque) - 8 times, and in humans - 45 times (spinal cord weight 30 g, head - 1500 g) . According to Ranke, the spinal cord by weight in mammals is 22-48% of the weight of the brain, in the gorilla - 5-6%, in humans - only 2%.
2. The weight of the brain. In terms of the absolute weight of the brain, a person does not take first place, since in large animals the brain is heavier than that of a person (1500 g): in a dolphin - 1800 g, in an elephant - 5200 g, in a whale - 7000 g. To reveal the true ratios of brain weight to body weight, recently they began to define the "square index of the brain", that is, the product of the absolute weight of the brain by the relative one. This pointer made it possible to distinguish a person from the entire animal world.
So, in rodents it is 0.19, in carnivores - 1.14, in cetaceans (dolphins) - 6.27, in anthropoids - 7.35, in elephants - 9.82, and, finally, in humans - 32, 0.
3. The predominance of the cloak over the brain stem, i.e., the new brain (neencephalon) over the old (paleencephalon).
4. The highest development of the frontal lobe of the brain. According to Brodman, 8-12% of the entire surface of the hemispheres falls on the frontal lobes in lower monkeys, 16% in anthropoid monkeys, and 30% in humans.
5. The predominance of the new cerebral cortex over the old (see Fig. 301).
6. The predominance of the cortex over the "subcortex", which in humans reaches maximum figures: the cortex, according to Dalgert, makes up 53.7% of the total brain volume, and the basal ganglia - only 3.7%.
7. Furrows and convolutions. Furrows and convolutions increase the area of the cortex of gray matter, therefore, the more developed the cortex of the cerebral hemispheres, the greater the folding of the brain. The increase in folding is achieved by the large development of small furrows of the third category, the depth of the furrows and their asymmetric arrangement. Not a single animal has at the same time such a large number of furrows and convolutions, while being as deep and asymmetrical as in humans.
8. The presence of a second signaling system, the anatomical substrate of which is the most superficial layers of the cerebral cortex.
Summing up the above, we can say that the specific features of the structure of the human brain, which distinguish it from the brain of the most highly developed animals, are the maximum predominance of the young parts of the central nervous system over the old ones: the brain - over the spinal cord, the cloak - over the trunk, the new cortex - over the old, superficial layers of the cerebral cortex - over the deep ones.
