Localization of functions in the cerebral cortex. Localization of functions in the cortex Main centers of the cerebral cortex Frontal lobe
The cerebral hemispheres are the most massive part of the brain. They cover the cerebellum and brain stem. The cerebral hemispheres make up approximately 78% of the total brain mass. During the ontogenetic development of the organism, the cerebral hemispheres develop from the cerebral vesicle of the neural tube, therefore this part of the brain is also called the telencephalon.
The cerebral hemispheres are divided along the midline by a deep vertical fissure into the right and left hemispheres.
In the depths of the middle part, both hemispheres are connected to each other by a large commissure - the corpus callosum. Each hemisphere has lobes; frontal, parietal, temporal, occipital and insula.
The lobes of the cerebral hemispheres are separated from one another by deep grooves. The most important are three deep grooves: the central (Rolandian) separating the frontal lobe from the parietal, the lateral (Sylvian) separating the temporal lobe from the parietal, the parieto-occipital separating the parietal lobe from the occipital on the inner surface of the hemisphere.
Each hemisphere has a superolateral (convex), inferior and internal surface.
Each lobe of the hemisphere has cerebral convolutions separated from each other by grooves. The top of the hemisphere is covered with a cortex ~ a thin layer of gray matter, which consists of nerve cells.
The cerebral cortex is the youngest formation of the central nervous system in evolutionary terms. In humans it reaches its highest development. The cerebral cortex is of great importance in the regulation of the body’s vital functions, in the implementation of complex forms of behavior and the development of neuropsychic functions.
Under the cortex is the white matter of the hemispheres; it consists of processes of nerve cells - conductors. Due to the formation of cerebral convolutions, the total surface of the cerebral cortex increases significantly. The total area of the cerebral cortex is 1200 cm2, with 2/3 of its surface located deep in the grooves, and 1/3 on the visible surface of the hemispheres. Each lobe of the brain has a different functional significance.
The cerebral cortex is divided into sensory, motor and associative areas.
The sensory areas of the cortical ends of the analyzers have their own topography and certain afferents of the conducting systems are projected onto them. The cortical ends of the analyzers of different sensory systems overlap. In addition, in each sensory system of the cortex there are polysensory neurons that respond not only to “their” adequate stimulus, but also to signals from other sensory systems.
The cutaneous receptive system, thalamocortical pathways, project to the posterior central gyrus. There is a strict somatotopic division here. The receptive fields of the skin of the lower extremities are projected onto the upper sections of this gyrus, the torso onto the middle sections, and the arms and head onto the lower sections.
Pain and temperature sensitivity are mainly projected onto the posterior central gyrus. In the cortex of the parietal lobe (fields 5 and 7), where the sensitivity pathways also end, a more complex analysis is carried out: localization of irritation, discrimination, stereognosis. When the cortex is damaged, the functions of the distal parts of the extremities, especially the hands, are more severely affected. The visual system is represented in the occipital lobe of the brain: fields 17, 18, 19. The central visual pathway ends in field 17; it informs about the presence and intensity of the visual signal. In fields 18 and 19, the color, shape, size, and quality of objects are analyzed. Damage to field 19 of the cerebral cortex leads to the fact that the patient sees, but does not recognize the object (visual agnosia, and color memory is also lost).
The auditory system is projected in the transverse temporal gyri (Heschl's gyrus), in the depths of the posterior sections of the lateral (Sylvian) fissure (fields 41, 42, 52). It is here that the axons of the posterior colliculi and lateral geniculate bodies end. The olfactory system projects to the region of the anterior end of the hippocampal gyrus (field 34). The bark of this area has not a six-layer, but a three-layer structure. When this area is irritated, olfactory hallucinations are observed; damage to it leads to anosmia (loss of smell). The taste system is projected in the hippocampal gyrus adjacent to the olfactory area of the cortex.
Motor areas
For the first time, Fritsch and Gitzig (1870) showed that stimulation of the anterior central gyrus of the brain (field 4) causes a motor response. At the same time, it is recognized that the motor area is an analytical one. In the anterior central gyrus, the zones, the irritation of which causes movement, are presented according to the somatotopic type, but upside down: in the upper parts of the gyrus - the lower limbs, in the lower - the upper. In front of the anterior central gyrus lie premotor fields 6 and 8. They organize not isolated, but complex, coordinated, stereotyped movements. These fields also provide regulation of smooth muscle tone, plastic muscle tone through subcortical structures. The second frontal gyrus, occipital, and superior parietal regions also take part in the implementation of motor functions. The motor area of the cortex, like no other, has a large number of connections with other analyzers, which apparently determines the presence of a significant number of polysensory neurons in it.
Architectonics of the cortex cerebral hemispheres brain
The study of the structural features of the structure of the cortex is called architectonics. Cells of the cerebral cortex are less specialized than neurons in other parts of the brain; nevertheless, certain groups of them are anatomically and physiologically closely related to certain specialized parts of the brain.
The microscopic structure of the cerebral cortex is different in its different parts. These morphological differences in the cortex allowed us to identify separate cortical cytoarchitectonic fields. There are several options for classification of cortical fields. Most researchers identify 50 cytoarchitectonic fields. Their microscopic structure is quite complex.
The cortex consists of 6 layers of cells and their fibers. The main type of structure of the bark is six-layered, however, it is not uniform everywhere. There are areas of the cortex where one of the layers is significantly expressed and the other is weakly expressed. In other areas of the cortex, some layers are subdivided into sublayers, etc.
It has been established that areas of the cortex associated with a specific function have a similar structure. Areas of the cortex that are close in their functional significance in animals and humans have a certain similarity in structure. Those parts of the brain that perform purely human functions (speech) are present only in the human cortex, and are absent in animals, even monkeys.
The morphological and functional heterogeneity of the cerebral cortex made it possible to identify the centers of vision, hearing, smell, etc., which have their own specific localization. However, it is incorrect to talk about the cortical center as a strictly limited group of neurons. The specialization of areas of the cortex is formed in the process of life. In early childhood, the functional zones of the cortex overlap each other, so their boundaries are vague and indistinct. Only in the process of learning, gaining personal experience practical activities there is a gradual concentration of functional zones into centers separated from each other. The white matter of the cerebral hemispheres consists of nerve conductors. In accordance with the anatomical and functional features white matter fibers are divided into associative, commissural and projection. Association fibers unite different areas of the cortex within one hemisphere. These fibers are short and long. Short fibers usually have an arcuate shape and connect adjacent gyri. Long fibers connect distant areas of the cortex. Commissal fibers are usually called those fibers that connect topographically identical areas of the right and left hemispheres. Commissural fibers form three commissures: the anterior white commissure, the fornix commissure, and the corpus callosum. The anterior white commissure connects the olfactory areas of the right and left hemispheres. The fornix commissure connects the hippocampal gyri of the right and left hemispheres. The bulk of the commissural fibers passes through the corpus callosum, connecting symmetrical areas of both hemispheres of the brain.
Projection fibers are those that connect the cerebral hemispheres with the underlying parts of the brain - the brainstem and spinal cord. The projection fibers contain pathways carrying afferent (sensitive) and efferent (motor) information.
The cerebral cortex is the evolutionarily youngest formation, which in humans has reached its greatest values 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 body’s vital functions, the implementation of complex forms of behavior and 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, we should not forget that this higher department can function normally only in close interaction with subcortical formations. The contrast between the cortex and underlying parts of the brain is largely schematic and conditional. In recent years, ideas about the vertical organization of the functions of the nervous system and about circular cortical-subcortical connections have been developing.
The cells of the cortex 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; damage to fairly large areas of the cortex can clinically appear very blurred (the so-called clinical silent zones). The absence of narrow specialization of cortical neurons creates conditions for the emergence of a wide variety of interneuron connections, the formation of complex “ensembles” of neurons that regulate various functions. This is the most important basis of learning ability. The theoretically possible number of connections between the 14 billion cells of the cerebral cortex is so large 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 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 different areas of the cortex allows us to speak about the cortical centers of vision, hearing, touch, etc., which have a specific localization. In the works of researchers of the 19th century, this principle of localization was taken to the extreme: attempts were made to identify centers of will, thinking, the ability to understand art, etc. At present, it would be incorrect to talk about 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 part of the analyzer, consists of a “core” and “scattered elements.” The “nucleus” is a relatively morphologically homogeneous group of cells with a precise 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 compared to 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 are built systems of “secondary” zones (layers II and III), in which associative connections with other parts of the cortex predominate, therefore they are also called projection-associative.
Thus, two groups of cellular zones are identified in the cortical representations of the analyzers. 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 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 have shown that stimulation 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 flickering light points, lines, etc. With irritation of the secondary zones, 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 overlap of cortical representations of individual analyzers, are distinguished in the cortex. In humans, they occupy a very significant place and are located primarily in the parieto-temporo-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, 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 does a constant concentration of functional zones occur into delineated centers separated from each other. In the clinic, adult patients experience very constant symptom complexes when certain areas of the cortex and associated nerve pathways are affected.
In childhood, due to incomplete differentiation of functional zones, focal damage to 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, we can distinguish the main integrative levels of cortical activity.
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 arriving 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 concentration of attention on certain of its details, voluntary movements with active strengthening or inhibition of them.
More difficult functional level cortical activity unites the systems of various analyzers, includes a second signaling system)", unites the systems of various analyzers, making it possible for a meaningful perception of the environment, an attitude towards the surrounding world “with knowledge and understanding.” This level of integration is closely related to speech activity, and understanding speech (speech gnosis) and the use of speech as a means of address and thinking (speech praxis) are not only interrelated, but also determined by various neurophysiological mechanisms, which is of great clinical importance.
Highest level 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 currently have highest value, from secondary signals, the implementation of probabilistic forecasting of the future and the formation of long-term 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 recording information (memorization), but also the functions of obtaining the necessary information from memory “storages” (memory), as well as the functions of transferring information flows from blocks of RAM (what is needed at the moment) into long-term memory blocks and vice versa. Otherwise, it would be impossible to learn 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's gyrus), taste analyzer, the anterior central gyrus - with the motor, and the posterior central gyrus - with the musculocutaneous analyzer. We can conditionally assume that these departments are associated with the first type of cortical activity and provide the simplest forms of gnosis and praxis.
Parts of the cortex located in the parietotemporal-occipital region take an active part in the formation of more complex gnostic-praxic functions. Damage to these areas leads to more complex forms of disorders. Wernicke's Gnostic speech center is located in the temporal lobe of the left hemisphere. The motor speech center is located somewhat anterior to the lower third of the anterior central gyrus (Broca's center). Besides the centers oral speech, distinguish between sensory and motor centers of written speech and a number of other formations, one way or another related to speech. The parieto-temporo-occipital region, where the pathways coming from various analyzers close, is of utmost importance for the formation of higher mental functions. The famous neurophysiologist and neurosurgeon W. Penfield called this area the interpretive cortex. In this area there are also formations involved in memory mechanisms.
Particular importance is attached to the frontal region. According to modern concepts, it is this section of the cerebral cortex that takes an active part in organizing purposeful activity, in long-term planning and determination, i.e. 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 (Brodmann's areas 4, 6 and 6a). In the middle layers there is an analyzer of kinesthetic stimuli coming from skeletal muscles, tendons, joints and bones. In layer V and partly VI, giant pyramidal cells of Betz are located, the fibers of which form the pyramidal path. The anterior central gyrus has a certain somatotopic projection and is connected with the opposite half of the body. The muscles of the lower extremities are projected in the upper parts of the gyrus, and the muscles of the face in the lower parts. The trunk, larynx, and 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 area (fields 8, 9). The work of this center is closely connected with the system of the posterior longitudinal fasciculus, the vestibular nuclei, formations of the striopallidal system, which is 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 there is a center that gives rise to the fronto-pontocerebellar 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 and sitting, and regulates the work of the opposite hemisphere of the cerebellum.
The motor speech center (speech praxis center) is located in the posterior part of the inferior frontal gyrus - Broca's gyrus (area 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, and is closely connected with the location posterior to it of the lower part of the anterior central gyrus (projection zone of the lips, tongue and larynx) and with that located in front of it 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 area of the hand (field 6). The center ensures the automaticity 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 superior parietal region (fields 5 and 7). In the posterior central gyrus, tactile, pain, and temperature sensitivity of the opposite half of the body is projected. The sensitivity of the leg is projected in the upper sections, and the sensitivity of the face is projected in the lower sections. Boxes 5 and 7 represent elements of deep sensitivity. Posterior to 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.
Posterior to the upper parts of the posterior central gyrus is a center that provides the ability to recognize one’s own body, its parts, their proportions and relative positions (field 7).
The center of praxis is localized in the inferior parietal lobule on the left, the supramarginal gyrus (fields 40 and 39). The center provides storage and implementation of images of motor automatisms (praxis functions).
In the lower parts of the anterior and posterior central gyri there is the center of the analyzer of interoceptive impulses of internal organs and blood vessels. The center has close connections with subcortical vegetative formations.
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's gyrus, areas 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, and is in close connection with the lower basal parts of the temporal lobes, giving rise to the occipitotemporal cortical-pontine-cerebellar pathway.
Rice. 55. Scheme of localization of functions in the cerebral cortex (A - D). I - projection motor zone; II - center of rotation of 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 diagram; IX - stereognosis zone; X - gnostic visual zone; XI - Gnostic reading zone; XII - gnostic speech zone; XIII - praxis zone; XIV - praxic speech zone; XV - practical 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 ammon's horn (field 11a, e) and provides projection function, as well as 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's horn, but, in addition, in the lowest part of the posterior central gyrus (area 43), as well as in the insula. Like the olfactory analyzer, the center provides projection function, storage and recognition of taste images.
The acoustic-gnostic sensory speech center (Wernicke's center) is localized in the posterior parts of the superior temporal gyrus on the left, in the depth of the lateral sulcus (area 42, as well as areas 22 and 37). The center provides recognition and storage of sound images of oral speech, both one’s own and others’.
In the immediate vicinity of Wernicke's center (the middle third of the superior temporal gyrus - area 22) there is a center that ensures the 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 written speech analyzer (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 language images.
Data on the localization of functions were obtained either as a result of irritation of various parts of the cortex in an experiment, or as a result of the analysis of disturbances arising as a result of 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 or 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, in childhood, phenomena of delayed or impaired development of cortical functions are observed, which significantly modifies the “classical” 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 location.
Depending on the types of cortical activity, it is possible to distinguish among cortical lesions disturbances of gnosis and praxis on different levels integration; speech disorders due to their practical importance; disorders of regulation of purposefulness, purposefulness of neurophysiological functions. With each type of disorder, the memory mechanisms involved in a given functional system may also be disrupted. In addition, more total memory impairment is possible. In addition to relatively local cortical symptoms, more diffuse symptoms are also observed in the clinic, manifesting primarily in intellectual disability and behavioral disorders. Both of these disorders are of particular importance in child psychiatry, although in essence 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 and maintain a relaxed tone of conversation with him. Since many diagnostic tasks presented to a child are very complex, one must strive to ensure that he not only understands the task, but also becomes interested in it. Sometimes when examining children who are overly distracted, motorically disinhibited, or mentally retarded, a lot of patience and ingenuity must be applied to identify existing abnormalities. In many cases, the analysis of a child’s cortical functions is helped by parents’ reports about his behavior at home, at school, and school characteristics.
When studying cortical functions, it is important psychological experiment, the essence of which is the presentation of standardized, targeted tasks. Certain psychological methods allow one to evaluate certain aspects of mental activity in isolation, while others allow them to be assessed more comprehensively. These include so-called personality tests.
Gnosis and its disorders. Gnosis literally means recognition. Our orientation in the surrounding world is associated with recognizing the shape, size, spatial relationship of objects and, finally, understanding their meaning, which is contained in the name of the object. This stock of information about the surrounding world consists of the analysis and synthesis of sensory impulse flows and is stored in memory systems. The receptor apparatus and the transmission of sensory impulses with lesions of higher gnostic mechanisms are preserved, but the interpretation of these impulses and the comparison of the received data with images stored in memory are disrupted. As a result, a disorder of gnosis occurs - agnosia, the essence of which is that while the perception of objects is preserved, the feeling of their “familiarity” is lost and the world, previously so familiar in detail, becomes alien, incomprehensible, devoid of meaning.
But gnosis cannot be imagined as a simple comparison, recognition of an image. Gnosis is a process of continuous updating, clarification, concretization of the image stored in the memory matrix, under the influence of its repeated comparison with the received information.
Total agnosia, in which complete disorientation is observed, is rare. Much more often, gnosis is disrupted in any one analytical system, and depending on the degree of damage, the severity of agnosia varies.
Visual agnosia occur when the occipital cortex is damaged. 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 an object (color, shape, size), but cannot recognize the object. For example, a patient describes an apple as “something round and pink,” without recognizing the apple as an apple. But if you give this object to the patient, 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 based on some other characteristics (clothing, mole, etc.). In other cases of agnosia, the patient 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 impaired. In practice, even if an object is not recognized, we can talk about violations of memory mechanisms, since the perceived object cannot be compared with its image in the Gnostic matrix. But there are also cases when, when an object is presented again, the patient says that he has already seen it, although he still cannot recognize it. If spatial orientation is impaired, 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, recognition of letters and numbers also suffers, and loss of reading ability occurs. The isolated type of this disorder will be analyzed in the analysis of speech function.
To study visual gnosis, a set of objects is used. Presenting them to the subject, they are asked to identify and describe them. appearance, compare which objects are larger and which are smaller. They also use a set of pictures, color, plain and outline. They evaluate not only the recognition of objects, faces, but also plots. At the same time, you can test 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, persistence, and fatigue are also taken into account.
It should be borne in mind that children recognize contour pictures worse than colored and monochromatic ones. Understanding the plot is related to the child’s age and degree of mental development. At the same time, agnosia in the classical form is rare in children due to incomplete differentiation of cortical centers.
Auditory agnosia. They occur when the temporal lobe is damaged in the area of Heschl’s gyrus. The patient cannot recognize previously familiar sounds: the ticking of a clock, the ringing of a bell, the sound of flowing water. Possible impairment of recognition of musical melodies - amusia. In some cases, the determination of the direction of sound is disrupted. In some types of auditory agnosia, the patient is unable to distinguish the frequency of sounds, such as metronome beats.
Sensitive agnosia are caused by impaired recognition of tactile, pain, temperature, proprioceptive images or their combinations. They occur when the parietal region is damaged. This includes astereognosis, body diagram disorders. In some variants of astereognosis, the patient not only cannot identify an object by touch, but is also unable to determine the shape of the object or the features of its surface. Sensitive agnosia also includes anosognosia, in which the patient is not aware of his defect, for example, paralysis. Phantom sensations can be attributed to disorders of sensitive gnosis.
When examining children, it should be borne in mind that a small child cannot always show parts of his body correctly; The same applies to patients suffering from dementia. In such cases, there is, of course, no need to talk about a disorder of the body diagram.
Taste and olfactory agnosia are rare. In addition, recognition of odors is very individual and is largely related to personal experience person.
Praxis and its disorders. Praxis refers to purposeful action. A person learns a lot of special motor acts in the course of life. Many of these skills, being formed with the participation of higher cortical mechanisms, are automated and become the same integral 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 of tone or coordination, and even simple voluntary movements are possible, but more complex, purely human motor acts are disrupted. 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 when the parieto-temporo-occipital region of the dominant hemisphere is affected. 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 detected only on the left. With apraxia, the plan of action suffers, i.e., the formation 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 was already ideal before the start of this process, that is, in the mind of the worker.”
Due to a violation of the action plan, when trying to complete a task, the patient makes many unnecessary movements. In some cases, parapraxia is observed when an action is performed that is only vaguely reminiscent of the given task. Sometimes perseverations are also observed, i.e. getting stuck on some actions. For example, the patient is asked to make an inviting movement with his hand. After completing this task, they offer to wag their 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, screwdriver, etc.).
According to clinical manifestations, several types of apraxia are distinguished: motor, ideational and constructive.
Motor apraxia. The patient cannot perform actions according to instructions or even imitation. He is asked to cut paper with scissors, lace a shoe, line 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 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 a task with real and imaginary objects (for example, show how to comb one's hair, stir sugar in a glass, etc.), while at the same time the actions of imitation are preserved. In some cases, the patient can automatically perform certain actions without thinking. For example, he purposefully cannot fasten a button, but performs this action automatically.
Constructive apraxia. The patient can perform various actions by imitation and by verbal orders, but is unable to create a qualitatively new motor act, put together a whole from parts, for example, make a certain figure out of matches, put together a pyramid, etc.
Some variants of apraxia are associated with impaired gnosis. The patient does not recognize the object or his body diagram is disturbed, so he is unable to perform tasks or performs them uncertainly and not entirely correctly.
To study praxis, a number of tasks are offered (sit down, shake a finger, comb your hair, etc.). They are also presented with tasks for actions with imaginary objects (they are asked to show how they eat, how they make phone calls, how they cut wood, etc.). Assess 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 Seguin boards with recesses different shapes, into which you need to insert the shapes corresponding to the recesses. This method also allows you to assess the degree of mental development. The Koss technique is also used: a set of cubes of different colors. From these cubes you need to put together a pattern that matches the one shown in the picture. Older children are also offered a Link cube: they 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 him to put it back together.
In these methods, how the child performs the task is of great importance: whether he acts by trial and error or according to a specific plan.
Rice. 56. Diagram of connections of speech centers and regulation of speech activity.
1 - writing center; 2 - Broca's center; 3 - center of praxis; 4 - center of proprioceptive gnosis; 5 - reading center; 6 - Wernicke center; 7 - center of auditory gnosis; 8 - center of visual gnosis.
It is important to remember that praxis develops as the child matures, so young children cannot yet perform such simple actions as combing their hair, fastening buttons, etc. Apraxia in its classic form, like agnosia, occurs mainly in adults.
Speech and its disorders. IN Visual, auditory, motor and kinesthetic analyzers take part in the implementation of speech functions, 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 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 multi-stage organization (Fig. 56).
Speech is the most important human function, therefore, cortical speech zones located in the dominant hemisphere (Broca's and Wernicke's centers), motor, kinetic, auditory and visual areas, as well as 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 and multi-stage nature of speech mechanisms also determines the variety of speech disorders. When the innervation of the speech apparatus is disrupted, dysarthria- articulation disorder, which may be caused by central or peripheral paralysis of the speech-motor apparatus, damage to the cerebellum, or striopallidal system.
There are also dyslalia- phonetically incorrect pronunciation individual sounds. Dyslalia can be functional in nature and can be quite successfully eliminated with speech therapy sessions. Under alalia understand the delay speech development. Usually to V.A. At the age of 10 years, the child begins to speak, but sometimes this happens much later, although the child understands speech addressed to him well. 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 is lagging behind in mental development, and therefore his speech is not formed. These different cases of alalia need to be differentiated, as they have different prognoses.
With the development of speech function in the dominant hemisphere (in the left for right-handers, in the right for left-handers), gnostic and practical speech centers are formed, and subsequently - writing and reading centers.
Cortical speech disorders are variants of agnosia and apraxia. There are expressive (motor) and impressive (sensory) speech. Cortical motor speech disorder is apraxia of speech, sensory speech - speech agnosia. In some cases, the recall of the necessary words is impaired, i.e., memory mechanisms suffer. Speech agnosia and apraxia are called aphasia.
It should be remembered that speech disorders can be a consequence 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, and stick out his tongue. These cases are not aphasias; speech apraxia here arises secondarily 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—decay of all components of speech as a result of damage to cortical speech areas;
2) alalia - systemic underdevelopment of speech due to lesions of cortical speech zones in the pre-speech period;
3) dysarthria - a violation of the sound-pronunciation aspect of speech as a result of a violation of the innervation of the speech muscles.
Depending on the location of the lesion, several forms of dysarthria are distinguished.
II. Speech disorders associated with functional changes
central nervous system:
1) stuttering;
2) mutism and surdomutism.
III. Speech disorders associated with defects in the structure of the articulatory apparatus (mechanical dyslalia, rhinolalia).
IV. Delays in speech development of various origins (due to prematurity, somatic weakness, pedagogical neglect, etc.).
Sensory aphasia(Wernicke's aphasia), or verbal “deafness,” occurs when the left temporal region is damaged (the middle and posterior parts 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 hearing phonemes that are 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 impaired. The severity of these disorders may vary. In the most severe cases, the addressed speech is not perceived at all and seems to be speech in foreign language. This form occurs when the posterior part of the superior temporal gyrus of the left hemisphere is damaged - Brodmann area 22.
Motor cortex areas. Movements occur when the cortex is stimulated in the area of the precentral gyrus. The area that controls the movements of the hand, tongue, and facial muscles is especially large.
Sensory cortex: somatic (skin) Human sensitivity, feelings of touch, pressure, cold and heat are projected into the postcentral gyrus. In the upper part there is a projection of the skin sensitivity of the legs and torso, lower - the arms and even lower - the head. Proprioceptive sensitivity (muscle feeling) projects to the postcentral and precentral gyri . Visual area cortex is located in the occipital lobe. Auditory zone The cortex is located in the temporal lobes of the cerebral hemispheres. Olfactory zone The cortex is located at the base of the brain. Projection taste analyzer , localized in the area of the mouth and tongue of the postcentral gyrus .
Association areas of the cortex. The neurons of these areas are not connected either to the sense organs or to the muscles; they communicate between different areas of the cortex, integrating, combining all impulses entering the cortex into integral acts of learning (reading, speech, writing), logical thinking, memory and providing the possibility of expedient behavior reactions. These areas include the frontal and parietal lobes of the cerebral cortex, which receive information from the association nuclei of the thalamus.
Lateral ventricles(right and left) are cavities of the telencephalon, lie below the level of the corpus callosum in both hemispheres and communicate through the interventricular foramina with the third ventricle. They are irregular in shape and consist of anterior, posterior and lower horns and a central part connecting them.
Topic 17. Basal ganglia
The basal ganglia of the telencephalon are accumulations of gray matter within the hemispheres. These include striatum (striatum), consisting of caudate and lenticular nuclei interconnected. The lentiform nucleus is divided into two parts: located outside shell and lying inside pale ball. The caudate nucleus and putamen are united into neostriatum. They are subcortical motor centers. Outside the lenticular nucleus there is a thin plate of gray matter - the fence. In the anterior part of the temporal lobe lies amygdala. Between the basal ganglia and the thalamus there are layers of white matter, the internal, external and outermost capsules. Conducting pathways pass through the internal capsule.
Topic 1. Limbic system
The telencephalon contains the formations that make up the limbic system: the cingulate gyrus, hippocampus, mammillary bodies, anterior thalamus, amygdala, fornix, septum pellucida, hypothalamus. They are involved in maintaining the constancy of the internal environment of the body, regulating autonomic function and forming emotions and motivations. This system is otherwise called the “visceral brain.” Information from internal organs comes here. When the limbic cortex is irritated, autonomic functions change: blood pressure, breathing, movements of the digestive tract, tone of the uterus and bladder.
Topic 19. Liquid media of the central nervous system: circulatory and liquor systems.Blood-brain barrier.
Blood supply The brain is carried out by the left and right internal carotid and branches of the vertebral arteries. Formed at the base of the brain arterial circle(Circle of Willis), which provides favorable conditions for blood circulation in the brain. The left and right anterior, middle and posterior cerebral arteries pass from the arterial circle to the hemispheres. Blood from the capillaries collects in the venous vessels and flows from the brain into the sinuses of the dura mater.
Liquor system of the brain. The brain and spinal cord are washed by cerebrospinal fluid (CSF), which protects the brain from mechanical damage, maintains intracranial pressure, and takes part in the transport of substances from the blood to brain tissue. From the lateral ventricles, cerebrospinal fluid flows through the foramen of Monro into the third ventricle and then through the aqueduct into the fourth ventricle. From it, the cerebrospinal fluid passes into the spinal canal and into the subarachnoid space.
Blood-brain barrier. Between neurons and blood in the brain there is a so-called blood-brain barrier, which ensures the selective flow of substances from the blood to nerve cells. This barrier performs a protective function, as it ensures the constancy of the cerebrospinal fluid. It consists of astrocytes, endothelial cells of capillaries, epithelial cells of the choroid plexuses of the brain.
Seminar topics
1. The role of spinal and cranial nerves in the perception of sensory information
2. The role of the telencephalon in the perception of signals from the external and internal environment
3. The main stages of the evolution of the central nervous system and ontogenesis of the nervous system
4. Brain diseases
5. Brain aging
Tasks for independent work
1. Draw a frontal section of the spinal cord with all the symbols known to you.
2. Draw a sagittal section of the brain indicating all its parts.
3. Draw a sagittal section of the spinal cord and brain, indicating all the cavities of the brain.
4. Draw a sagittal section of the brain with all the structures known to you.
Questions for self-control
1. Define the basic concepts of the anatomy of the central nervous system:
The concept of the nervous system;
Central and peripheral nervous system;
Somatic and autonomic nervous system;
Axes and planes in anatomy.
2. What is the main structural unit of the nervous system?
3. Name the main structural elements of a nerve cell.
4. Give a classification of nerve cell processes.
5. List the sizes and shapes of neurons. Tell us about the use of microscopic technology.
6. Tell us about the nucleus of a nerve cell.
7. What are the main structural elements of neuroplasm?
8. Tell us about the nerve cell membrane.
9. What are the main structural elements of a synapse?
10. What is the importance of mediators in the nervous system?
11. What are the main types of glia in the nervous system?
12. What is the role of the myelin sheath of the nerve fiber for conducting nerve impulses?
13. Name the types of nervous system in phylogeny.
14. List the structural features of the reticular nervous system.
15. List the structural features of the nodal nervous system.
16. List the structural features of the tubular nervous system.
17. Expand the principle of bilateral symmetry in the structure of the nervous system.
18. Expand the principle of cephalization in the development of the nervous system.
19. Describe the structure of the nervous system of coelenterates.
20. What is the structure of the nervous system of annelids?
21. What is the structure of the nervous system of mollusks?
22. What is the structure of the nervous system of insects?
23. What is the structure of the nervous system of vertebrates?
24. Give a comparative description of the structure of the nervous system of lower and higher vertebrates.
25. Describe the formation of the neural tube from the ectoderm.
26. Describe the stage of three brain vesicles.
27. Describe the stage of five brain vesicles.
28. The main parts of the central nervous system in a newborn.
29. Reflex principle of the structure of the nervous system.
30. What is the general structure of the spinal cord?
31. Describe the segments of the spinal cord.
32. What is the purpose of the anterior and posterior roots of the spinal cord?
33. Segmental apparatus of the spinal cord. What is the organization of the spinal reflex?
34. What is the structure of the gray matter of the spinal cord?
35. What is the structure of the white matter of the spinal cord?
36. Describe the commissural and suprasegmental apparatus of the spinal cord.
37. What is the role of the ascending tracts of the spinal cord in the central nervous system?
38. What is the role of the descending tracts of the spinal cord in the central nervous system?
39. What are spinal nodes?
40. What are the consequences of spinal cord injuries?
41. Describe the development of the spinal cord in ontogenesis.
42. What are the structural features of the main membranes of the central nervous system?
43. Describe reflex principle CNS organizations.
44. Name the main parts of the rhombencephalon.
45. Describe the dorsal surface of the medulla oblongata.
46. Describe the ventral surface of the medulla oblongata.
47. What are the functions of the main nuclei of the medulla oblongata?
48. What are the functions of the respiratory and vasomotor centers of the medulla oblongata?
49. What is the general structure of the fourth ventricle, the cavity of the rhombencephalon?
50. Name the structural features and functions of the cranial nerves.
51. List the characteristics of the sensory, motor and autonomic nuclei of the cranial nerves.
52. What is the purpose of the bulbar parasympathetic center of the brain?
53. What are the consequences of bulbar disorders?
54. What is the general structure of the bridge?
55. List the nuclei of the cranial nerves lying at the level of the pons.
56. What reflexes in the central nervous system correspond to the auditory and vestibular nuclei of the pons?
57. Explain the ascending and descending paths of the bridge.
58. What are the functions of the lateral and medial lemniscal tracts?
59. What is the purpose of the reticular formation of the brain stem in the central nervous system?
60. What is the role of the blue spot in the organization of brain functions. What is the noradrenergic system of the brain?
61. What is the role of the raphe nuclei in the central nervous system. What is the serotonergic system of the brain?
62. What is the general structure of the cerebellum. What are its functions in the central nervous system?
63. List the evolutionary formations of the cerebellum.
64. What are the connections of the cerebellum with other parts of the central nervous system. Anterior, middle and posterior cerebellar peduncles?
65. Cerebellar cortex. Tree of life of the cerebellum.
66. Describe the cellular structure of the cerebellar cortex.
67. What is the role of the subcortical nuclei of the cerebellum in the central nervous system?
68. What are the consequences of cerebellar disorders?
69. What is the role of the cerebellum in organizing movements?
70. Name the main functions in the central nervous system of the midbrain. What is the Sylvian aqueduct?
71. What is the structure of the roof of the midbrain. Anterior and posterior tubercles of the quadrigeminal and their purpose?
72. What is the purpose of the main tire cores?
73. What is the purpose of the mesencephalic parasympathetic center?
74. What is the periaqueductal gray matter needed for? Reveal the features of the organization of the pain system in the central nervous system.
75. What are the red nuclei of the midbrain. Define decerebrate rigidity?
76. Black nucleus and ventral tegmental area. What is the role of the brain's dopaminergic system in the central nervous system?
77. Descending and ascending pathways of the midbrain. Pyramidal and extrapyramidal systems of the central nervous system.
78. What is the structure and purpose of the cerebral peduncles?
79. What is the purpose of the dorsal and ventral chiasm of the midbrain?
80. Describe the general structure of the diencephalon and its main functions. What is the location of the third ventricle?
81. Name the main parts of the thalamic brain.
82. Describe the structure and functions of the thalamus.
83. Describe the structure and functions of the suprathalamic region.
84. Describe the structure and functions of the post-thalamic region.
85. What is the role of the hypothalamus in organizing the functions of the central nervous system?
86. Neurohumoral function of the brain. Epiphysis and pituitary gland, their location and purpose.
87. What is the role of the Peipets circle in the organization of adaptive behavior.
88. Hippocampus, its structure and functions.
89. Cingulate cortex, its structure and functions.
90. The amygdala complex, its structure and functions.
91. Emotional-motivational sphere and its brain support.
92. What are the “reward” and “punishment” systems of the brain? Self-irritation reaction.
93. Neurochemical organization of the brain’s reinforcing systems.
94. What are the consequences of damage to individual formations of the limbic system? Animal studies.
95. Describe the general structure of the telencephalon. What is its role in ensuring adaptive behavior in humans and animals?
96. Name the main functions of the striatum.
97. Evolutionary formations of the striatum.
98. Caudate nucleus, its location and purpose. Nigrostriatal system of the brain.
99. Ventral striatum, its structure and functions. Mesolimbic system of the brain.
100. General structure of the cerebral hemispheres (lobes, sulci, gyri).
101. Dorsolateral surface of the cerebral cortex.
102. Medial and basal surfaces of the cerebral cortex.
103. What is the role of interhemispheric asymmetry in the organization of adaptive behavior. Corpus callosum.
104. Cytoarchitecture of the cerebral cortex (cortical layers and Brodmann areas).
105. Evolutionary formations of the cerebral cortex (new cortex, old cortex, ancient cortex) and their functions.
106. Projection and associative areas of the cerebral cortex and their purpose.
107. Speech-sensory and speech-motor centers of the cerebral cortex.
108. Sensomotor cortex, its localization. Projections of the human body in the sensorimotor cortex.
109. Visual, auditory, olfactory, gustatory cortical projections.
110. Basics of topical diagnostics for damage to areas of the cerebral cortex.
111. Frontal and parietal cortex and their role in ensuring adaptive activity of the brain.
The cerebral cortex is the material basis of human mental activity. The cortex is gray matter with a thickness of 1.5 to 5 mm, contains 14 billion nerve cells and has a six-layer structure. The cortex is a huge nuclear center, a core spread over the surface of the hemispheres.
For more than 130 years, there has been a debate about whether there are centers in the cortex or not and to what extent they influence the “supervised” functions: 1. Are these centers literally responsible for everything (the center of tourism, love of painting, theater, etc.), or their influence is less detailed. 2. The cortex is one continuous screen center responsible for all functions.
Obviously, the truth, as always, is somewhere in the middle.
The founder of a detailed study of the cellular composition of the cortex was a Russian scientist, a resident of Kiev, Vladimir Alekseevich Betz. In 1874, he published the results of his research using his own method of serial sections and carmine staining. Betz identified the different structure of the cortex in its various parts and developed a map of the cytoarchitectonics of the cortex. Subsequently, other maps were created: Brodmann with 52 cytoarchitectonic fields, Vogt with 150 myeloarchitectonic fields, etc. Research is currently ongoing at the Brain Institute in Moscow and in other countries.
Ideas about the localization of functions in the cerebral cortex are of great practical importance for solving problems of the topic of lesions in the cerebral hemispheres. Everyday clinical experience shows that there are certain patterns in the dependence of functional disorders on the location of the pathological focus. Based on this, the clinician solves the problems of topical diagnostics. However, this is the case with simple functions: movement and sensitivity. Functions that are more complex, phylogenetically young, cannot be highly localized; in the implementation complex functions Very large areas of the cortex are involved, even the entire cortex.
Works by V.A. Betz were carefully studied by I.P. Pavlov. Taking these data into account, Ivan Petrovich Pavlov created the foundations of a new and progressive doctrine of the localization of functions in the brain. Pavlov considered the cerebral cortex as a collection of cortical ends of analyzers. Pavlov created the doctrine of analyzers. According to Pavlov, the analyzer is a nervous mechanism that analyzes the phenomena of external and inner world by decomposing a complex set of irritations into individual elements. It begins with the perceptive apparatus and ends in the brain, that is, the analyzer includes the receptor apparatus, the conductor of nerve impulses and the cortical center.
Pavlov proved that cortical end of the analyzer- This is not a strictly defined zone. It has a core and scattered elements. Core- the place of concentration of nerve cells, where higher analysis, synthesis and integration occur. On its periphery, in scattered elements, simple analysis and synthesis. The areas of scattered elements of neighboring analyzers overlap each other (Fig.).
According to Pavlov, the work of the second signaling system is inextricably linked with the functions of all analyzers, therefore it is impossible to imagine the localization of the complex functions of the second signaling system in limited cortical fields. Pavlov laid the foundations of the doctrine of dynamic localization of functions in the cortex. Ideas about the dynamic localization of functions in the cortex suggest the possibility of using the same cortical structures in various combinations to serve various complex cortical functions. Thus, associative pathways unite analyzers, contributing to the higher synthetic activity of the cerebral cortex. Today scientists know that irritation is transformed into excitation, which is transmitted to the cortical end of the analyzer. Another thing is not clear - where and how is arousal transformed into sensation? What structures are responsible for this? Thus, when the visual field is irritated in the area of the calcarine sulcus, “simple” hallucinations appear in the form of light or color spots, sparks, shadows. Irritation of the outer surface of the occipital lobe produces “complex” hallucinations in the form of figures and moving objects.
In the motor zone of the cortex, cells were found that produce a discharge of impulses to visual, auditory, and skin stimuli, and in the visual zone of the cortex, neurons were identified that respond with electrical discharges to tactile, sound, vestibular and olfactory stimuli. In addition, neurons were found that respond not only to “their” stimulus, as they now say, a stimulus of its modality, its own quality, but also to one or two strangers. They were called polysensory neurons.
This section of the anatomy of the NS is divided into the following subcategories
The question regarding the localization of functions in the cerebral cortex arose a long time ago. It was first performed by the Viennese doctor neuromorphologist F.J. Gall (1822). He drew attention to the fact that the configuration of the skull varies from person to person. In his opinion, this depends on the degree of development of certain areas of the cortex, which affect the structure of the skull and lead to the appearance of bulges and depressions on it. From these changes in the skull, Gall tried to determine the mental capabilities, abilities and inclinations of a person.
Gall's teaching was, of course, erroneous. It provided for the rough localization of complex mental processes in the cerebral cortex. After all, it is known that these processes occur diffusely.
The concept of localization psychomorphology by Gall was replaced by the position formulated by the French physiologists F. Magendie and M.Zh.P. Flourens (1825) that the cerebral cortex functions as a single whole and that there is no functional localization within the cortex. This is how the theory of equipotentiality, the equivalence of different parts of the cortex, arose. She not only refuted Gall’s primitive views, but also denied his correct idea about the possibility of localizing functions in the cortex and the need to study it.
Until 1860, it was believed that the cerebral cortex was functionally homogeneous and polyvalent and performed only the function of thinking. Soon, numerous evidence was obtained from both clinicians and physiologists regarding the localization of various functions in the cerebral cortex.
The specialized areas of the brain associated with speech function have been studied in most detail. In 1861, the French anatomist P. Broca showed that damage to the posterior third of the inferior frontal gyrus of the left hemisphere of the brain predetermines speech disorders - motor aphasia. This area was later called the Broca center (zone). In 1874, the German researcher K. Wernicke described the second type of aphasia - sensory. It is associated with damage to another area of the cortex, which is also located in the left hemisphere of the brain in the posterior third of the superior temporal gyrus. This area is now called the Wernicke center (zone). Later it was found that Wernicke's and Broca's centers are connected by a group of nerve fibers - an arcuate fascicle.
Of great importance was the discovery by A. Fritsch and E. Hitzig in 1870 of areas of the cortex, the irritation of which in an experiment on animals caused a motor effect, i.e. it was confirmed that motor centers are located in the cerebral cortex. After these works, the messages of G. Munch, V.M. aroused great interest. Bekhterev that the cerebral cortex contains not only motor centers, but also areas associated with vision, hearing, smell, taste, and general skin sensitivity. At the same time, numerous works by clinicians confirmed the existence of a functional localization in the human brain. G. Fleksig noted the leading role of the anterior parts of the frontal lobes and the inferior parietal gyrus in the course of mental processes.
In 1874 prof. V.M. Betz discovered in the motor cortex of monkeys and humans a special group of giant pyramidal neurons that form pathways between the motor cortex and the spinal cord. These giant cells are now called Betz cells.
This is how the doctrine of the narrow localization of functions in the cerebral cortex arose, which received a solid factual basis, a morphological basis.
The concept of localization at a certain stage in the development of science was progressive in comparison with the views of equipotentialists. It provided the ability to localize a significant number of functional disorders in the cerebral cortex. But the hopes associated with these important discoveries in neuroscience were far from being fully realized. Moreover, later this concept began to slow down the development of science, which led to increased criticism of the theory of narrow localization of functions. Further observations showed that higher mental functions are localized in the cerebral cortex, but their localization does not have clear boundaries. They were disrupted when different areas of the cortex were affected, significantly distant from one another.
What point of view should we take on this issue now? Modern concept about the localization of functions in the cerebral cortex is incompatible with both the theory of narrow localizationism and the ideas of equivalence (equipotentiality) different entities brain On the issue of localization of functions in the cerebral cortex, domestic neurology comes from the teachings of I.P. Pavlova on dynamic localization of functions. Based experimental research I.P. Pavlov showed that the cerebral cortex is represented by a set of analyzers, where each of them has a central zone - the analyzer core and a peripheral zone, where the cortical representation is scattered. Due to this structure of the analyzer, its cortical zones seem to overlap one another and form a closely connected morphofunctional association. The dynamic localization of functions in the cortex provides for the possibility of using the same brain structures to provide different functions. This means that different parts of the cerebral cortex take part in performing one or another function. For example, such higher mental processes as speech, writing, reading, counting, etc., are never carried out by one isolated center, but rely on a complex system of jointly functioning areas of the brain. Dynamic localization of functions does not exclude the presence of centers in the cerebral cortex, but their function is determined by connections with other areas of the cortex.
It should be noted that the degree of localization of different functions of the cortex is not the same. Only elementary cortical functions, which are provided by individual analyzers, primary receptor apparatuses, can be associated with the corresponding areas of the cortex. Complex, phylogenetically young functions cannot be narrowly localized; large areas of the cerebral cortex or even the cortex as a whole are involved in their implementation.
The doctrine of dynamic localization of functions in the cortex was further developed in the works of P.K. Anokhin (1955), who formulated the concept of functional systems of higher brain functions. In accordance with modern concepts, the functional system has a complex hierarchical structure. It includes cortical and subcortical centers, pathways, and executive organs in various connections. Moreover, the same nerve formations can be components of different functional systems. This or that higher brain function is directly realized thanks to the complex, ordered, dynamic interaction of different brain systems.
A significant contribution to the understanding of the functional organization of the cerebral cortex was made by the studies of the Canadian neurosurgeon W. Penfield (1964), conducted during surgery on the human brain. The main principle of the functional organization of projection systems in the cortex is the principle of topical localization, which is based on clear anatomical connections between individual perceptive elements of the periphery and the cortical cells of the projection zones. In each of these analyzer systems, depending on the relationship of different parts of the cortex to other brain formations, three types of cortical zeros are distinguished (G.I. Polyakov, 1973).
Primary projection fields correspond to those architectural areas in which the cortical sections of the analyzers are localized: the analyzer of general sensitivity - in the postcentral gyrus, the olfactory and auditory in the temporal lobe, the visual in the occipital lobe. Simple, elementary functions are associated with these fields: general skin sensitivity, hearing, smell, vision. These are fields that cannot provide an integrative function of perception; they only respond to certain stimulation of one modality and do not respond to stimulation of another. In the primary projection fields, the most developed neurons are the IV afferent layer. Primary projection fields are characterized by a somatotopic principle of structure, i.e., representation of sensitive functions in certain areas of the cortex.
Secondary projection fields are located around the primary ones. They are not directly related to specific pathways. In the secondary cortical fields, neurons of the second and third layers of the cortex predominate; there are a large number of multisensory neurons here, which provide, in comparison with the primary fields, a different response pattern. Electrical stimulation of the secondary projection fields causes complex visual images and melodies in a person, in contrast to the elementary sensations (flash, sound) that arise in the case of stimulation of the primary fields. In the secondary projection fields, higher analysis and synthesis, more detailed processing of information, and awareness of it occur.
Secondary projection fields, together with the primary ones, make up the central part of the analyzer, or its core. The interaction of neurons in these zones is complex and ambiguous, and under conditions of normal brain activity it is based on a sequential change in excitatory and inhibitory processes in accordance with the nature of the final result. This provides dynamic localization properties.
Described functional organization The cortex in the form of fields clearly separated according to the principle of modal specificity is most pronounced in humans and higher representatives of the animal world. In particular, in humans, secondary projection fields make up about 50% of the entire cerebral cortex (in monkeys - about 20%).
Tertiary projection fields are associative zones that are located in areas where individual analyzers overlap. There are two main association zones: in the frontal lobe in front of the precentral gyrus and on the border between the secondary projection fields of the parietal, occipital and temporal lobes.
Tertiary projection fields, or overlap zones, are not directly connected with the peripheral receptor apparatus, but they are closely connected with other areas of the cortex, including projection fields. Signals from the association nuclei of the thalamus also come here.
In the cerebral cortex, especially in the area of association zones, neurons are arranged like functional columns. The columnar organization of cortical zones is characterized by a vertical arrangement of neural elements (columns) with similar functional properties. This means that all six layers of cortical cells in the association zones, which lie perpendicular to its surface, take part in processing sensory information that comes from peripheral receptors. Most neurons in the tertiary zones have multimodal properties. They provide integration of signals that come from different analyzers. Here the formation of the corresponding feelings is completed, complex analytical and synthetic functions are carried out.
Tertiary projection fields are directly related to higher mental functions. The functions of these zones are associated with the processes of learning and memory. They are unique to the human brain.
The sensory areas of the cerebral cortex are closely connected with the motor areas, which are located in front of the central sulcus. Together they form a single sensorimotor field. The motor cortex is also divided into primary, secondary and tertiary zones.
The primary motor cortex (area 4) is located immediately anterior to the Rolandic sulcus. This is the precentral gyrus, from the 5th layer of which the pyramidal tract begins, which connects the cerebral cortex with the cells of the anterior horns of the spinal cord. Like the somatosensory zone, it has a clear somatotopic organization. Almost 50% of the surface of this zone in humans is represented by the upper limbs and muscles of the face, lips, tongue, given the importance of the function they perform (fine movements, speech).
The secondary motor cortex zone is premotor (field 6), located in front of the primary cortex zone and deep in the Sylvian fissure. This cortical area, together with the primary motor area, subcortical nuclei and thalamus, controls many more complex movements.
The tertiary motor cortex covers the anterior parts of the frontal lobes (prefrontal region). The neurons of this cortical zone receive numerous impulses that come from the sensorimotor cortex, visual and auditory cortex, thalamus, as well as from the subcortical nuclei and other structures. This zone ensures the integration of all information processes, the formation of plans and action programs, and controls the most complex forms of human behavior.
The primary sensory and motor areas of the cortex are connected primarily to the opposite half of the body. Due to this organization of contralateral connections, the sensory and motor functions of both hemispheres of the cerebrum in both humans and animals are symmetrical.
As for the secondary and tertiary zones of the cortex, they are different in the right and left hemispheres of the brain. This means that the distribution of more specialized functions is quite different asymmetric. It is believed that with the complication of brain function, the tendency towards a certain lateralization in its distribution increases. The development of lateralization of hemispheric centers is a distinctive feature of the human brain.
In the implementation of the functions of the cerebral cortex, a significant role belongs to the processes of excitation and inhibition in the central nervous system. Excitation is associated with the occurrence of temporary depolarization in the neuron. Excitatory mediators can be different substances: norepinephrine, dopamine, serotonin. Derivatives of glutamic acid (glutamates), substance P, are important. Inhibition in the cerebral cortex is carried out by inhibitory interneurons. The main mediator of cortical inhibition is GAM K. Overstrain of the processes of excitation and inhibition leads to the appearance of stagnant foci, disruption of cortical activity and the emergence of pathological conditions.
The processes of selective inhibition, which plays a decisive role in ensuring the direction of the flow of nerve impulses, are also essential. At the level of the cerebral cortex, it regulates the relationship between the symmetrical centers of both hemispheres. In addition, axonal collaterals of pyramidal cells through intercalary inhibitory Renshaw cells exert an inhibitory effect on adjacent neurons. This limits the level of excitation of the cerebral cortex and prevents the normal occurrence of epileptic activity in the brain. Since one neuron of the central nervous system has connections with many tens and hundreds of nerve fibers from different areas, an extremely complex combination of inhibitory and excitatory impulses arises, which significantly affect the functional state of brain neurons. Thanks to the convergent-divergent organization of the nervous system, such specific oscillations and the corresponding distribution of excitation and inhibition occur simultaneously in the cortical and subcortical neurons of the brain. This creates the basis for the integrative activity of the brain, with which higher mental functions are associated: perception, cognition, memory, state of consciousness.
Interhemispheric relationship
A characteristic feature of the human brain is the distribution of functions between the two hemispheres. The fact that the human brain is not completely symmetrical in its functions can be seen based on the facts of daily life. Hemispheric specialization is associated with the predominant use of one hand. This phenomenon is determined genetically. Most people prefer the right hand, which is controlled by the left half of the brain. In the human population, left-handers account for no more than 9%. It is possible that this significant shift toward right-hand dominance reflects a unique specialization of the human brain. Linguistic abilities are also associated with the left hemisphere of the brain. Recently it was believed that the left hemisphere of the brain is dominant, its development begins with the evolution of speech, and the right one plays a subordinate, subdominant role. However, recently this concept has been revised as it has become apparent that each hemisphere has certain characteristics, but different functions. The concept of a dominant and non-dominant hemisphere has been replaced by the concept of complementary (corresponding) hemispheric specialization.
The left hemisphere of the cerebrum plays an exceptional role in linguistic and speech activity and specializes in sequential analytical processes (categorical hemisphere). It is the basis of logical, abstract thinking and functions under the direct influence of the second signaling system. The right hemisphere of the brain is functionally connected with the perception and processing of exteroceptive, proprioceptive, interoceptive impulses, which provide the perception of specific images, objects, people, animals, i.e., they carry out a gnostic function, including the gnosis of one’s own body (representative hemisphere). Its importance in the perception of space, time, and music has been proven. The right hemisphere serves as the basis for imaginative, concrete thinking. Therefore it should not be considered right hemisphere large brain subordinate to the left. The result of the research recent years The theory of hemispheric dominance was replaced by the concept of complementary (corresponding) specialization of the hemispheres. Therefore, at present it can be argued that only one unique feature is characteristic of the human brain - functional asymmetry, the specialization of the cerebral hemispheres, which begins before the evolution of speech.
For many years, the dominant idea among neurologists was that cerebral hemisphere specialization does not correlate with anatomical asymmetry. However, over the past decades this issue has been reconsidered. Now asymmetry of the human brain is detected using computed axial tomography. There are reports of different distributions of mediators and enzymes, i.e., biochemical asymmetry of the cerebral hemispheres. The physiological significance of these differences is still unknown.
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