The cerebral cortex departments and functions. Functions of the human cerebral cortex

Reading functions are provided by the lexical center (the center of the lexicon). The center of the lexia is located in the angular gyrus.

Graphic analyzer, graphic center, writing function

Writing functions are provided by the graphic center (graphic center). The center of the graph is located in the posterior part of the middle frontal gyrus.

Counting Analyzer, Calculation Center, Counting Function

The functions of the account are provided by the counting center (calculation center). The center of calculation is located at the junction of the parieto-occipital region.

Praxis, praxis analyzer, praxis center

Praxis is the ability to perform purposeful motor acts. Praxis is formed in the process of human life, starting from infancy, and is provided by a complex functional system of the brain with the participation of the cortical fields of the parietal lobe (lower parietal lobule) and the frontal lobe, especially the left hemisphere in right-handed people. For normal praxis, the preservation of the kinesthetic and kinetic basis of movements, visual-spatial orientation, programming processes and control of purposeful actions are necessary. The defeat of the praxic system at one level or another is manifested by such a type of pathology as apraxia. The term "praxis" comes from the Greek word "praxis" which means "action". - this is a violation of a purposeful action in the absence of muscle paralysis and the preservation of its constituent elementary movements.

Gnostic center, center of gnosis

In the right hemisphere of the brain in right-handers, in the left hemisphere of the brain in left-handers, many gnostic functions are represented. With damage to the predominantly right parietal lobe, anosognosia, autopagnosia, and constructive apraxia may occur. The center of gnosis is also associated with ear for music, orientation in space, and the center of laughter.

memory, thinking

The most complex cortical functions are memory and thinking. These functions do not have a clear localization.

Memory, memory function

Various sections are involved in the implementation of the memory function. The frontal lobes provide active purposeful mnestic activity. The posterior gnostic sections of the cortex are associated with particular forms of memory - visual, auditory, tactile-kinesthetic. The speech zones of the cortex carry out the process of encoding incoming information into verbal logical-grammatical systems and verbal systems. The mediobasal regions of the temporal lobe, in particular the hippocampus, translate current impressions into long-term memory. The reticular formation ensures the optimal tone of the cortex, charging it with energy.

Thinking, the function of thinking

The function of thinking is the result of the integrative activity of the entire brain, especially the frontal lobes, which are involved in organizing the purposeful conscious activity of a person, man, woman. Programming, regulation and control take place. At the same time, in right-handers, the left hemisphere is the basis of predominantly abstract verbal thinking, and the right hemisphere is mainly associated with concrete figurative thinking.

The development of cortical functions begins in the first months of a child's life and reaches its perfection by the age of 20.

In subsequent articles, we will focus on topical issues of neurology: areas of the cerebral cortex, areas of the cerebral hemispheres, visual, area of ​​the cortex, auditory area of ​​the cortex, motor motor and sensitive sensory areas, associative, projection areas, motor and functional areas, speech areas, primary areas cerebral cortex, associative, functional zones, frontal cortex, somatosensory zone, cortical tumor, absence of the cortex, localization of higher mental functions, problem of localization, brain localization, concept of dynamic localization of functions, research methods, diagnostics.

Cortex treatment

Sarclinic uses proprietary methods for restoring the work of the cerebral cortex. Treatment of the cerebral cortex in Russia in adults, adolescents, children, treatment of the cerebral cortex in Saratov in boys and girls, boys and girls, men and women allows you to restore lost functions. In children, the development of the cerebral cortex, the centers of the brain, is activated. In adults and children, atrophy and subatrophy of the cerebral cortex, cortical disturbance, inhibition in the cortex, excitation in the cortex, damage to the cortex, changes in the cortex, sore cortex, vasoconstriction, poor blood supply, irritation and dysfunction of the cortex, organic damage, stroke, detachment , damage, diffuse changes, diffuse irritation, death, underdevelopment, destruction, diseases, question to the doctor If the cerebral cortex has suffered, then with proper and adequate treatment it is possible to restore its functions.

Text: ® SARCLINIC | Sarclinic.com \ Sarlinic.ru Photo: MedusArt / Photogenika Photobank / photogenica.ru The people shown in the photo are models, do not suffer from the described diseases and / or all coincidences are excluded.

Cortex - the highest department of the central nervous system, which ensures the functioning of the body as a whole in its interaction with the environment.

brain (cerebral cortex, neocortex) is a layer of gray matter, consisting of 10-20 billion and covering the large hemispheres (Fig. 1). The gray matter of the cortex makes up more than half of the total gray matter of the CNS. The total area of ​​the gray matter of the cortex is about 0.2 m 2, which is achieved by the sinuous folding of its surface and the presence of furrows of different depths. The thickness of the cortex in its different parts ranges from 1.3 to 4.5 mm (in the anterior central gyrus). The neurons of the cortex are arranged in six layers oriented parallel to its surface.

In the areas of the cortex related to, there are zones with a three-layer and five-layer arrangement of neurons in the structure of the gray matter. These areas of the phylogenetically ancient cortex occupy about 10% of the surface of the cerebral hemispheres, the remaining 90% are the new cortex.

Rice. 1. Mole of the lateral surface of the cerebral cortex (according to Brodman)

The structure of the cerebral cortex

The cerebral cortex has a six-layer structure

Neurons of different layers differ in cytological features and functional properties.

molecular layer- the most superficial. It is represented by a small number of neurons and numerous branching dendrites of pyramidal neurons lying in deeper layers.

Outer granular layer formed by densely spaced numerous small neurons of various shapes. The processes of the cells of this layer form corticocortical connections.

Outer pyramidal layer consists of pyramidal neurons of medium size, the processes of which are also involved in the formation of corticocortical connections between adjacent areas of the cortex.

Inner granular layer similar to the second layer in terms of cell type and fiber arrangement. In the layer there are bundles of fibers that connect various parts of the cortex.

Signals from specific nuclei of the thalamus are carried to the neurons of this layer. The layer is very well represented in the sensory areas of the cortex.

Inner pyramidal layers formed by medium and large pyramidal neurons. In the motor area of ​​the cortex, these neurons are especially large (50-100 microns) and are called giant, pyramidal Betz cells. The axons of these cells form fast-conducting (up to 120 m/s) fibers of the pyramidal tract.

Layer of polymorphic cells It is represented mainly by cells whose axons form corticothalamic pathways.

Neurons of the 2nd and 4th layers of the cortex are involved in the perception, processing of signals coming to them from the neurons of the associative areas of the cortex. Sensory signals from the switching nuclei of the thalamus come mainly to the neurons of the 4th layer, the severity of which is greatest in the primary sensory areas of the cortex. The neurons of the 1st and other layers of the cortex receive signals from other nuclei of the thalamus, the basal ganglia, and the brain stem. Neurons of the 3rd, 5th and 6th layers form efferent signals sent to other areas of the cortex and downstream to the underlying parts of the CNS. In particular, the neurons of the 6th layer form fibers that follow to the thalamus.

There are significant differences in the neuronal composition and cytological features of different parts of the cortex. According to these differences, Brodman divided the cortex into 53 cytoarchitectonic fields (see Fig. 1).

The location of many of these fields, identified on the basis of histological data, coincides in topography with the location of the cortical centers, identified on the basis of their functions. Other approaches to dividing the cortex into regions are also used, for example, based on the content of certain markers in neurons, according to the nature of neuronal activity, and other criteria.

The white matter of the cerebral hemispheres is formed by nerve fibers. Allocate association fibers, subdivided into arcuate fibers, but to which signals are transmitted between neurons of adjacent gyri and long longitudinal bundles of fibers that deliver signals to neurons of more distant parts of the hemisphere of the same name.

Commissural fibers - transverse fibers that transmit signals between neurons of the left and right hemispheres.

Projection fibers - conduct signals between the neurons of the cortex and other parts of the brain.

The listed types of fibers are involved in the creation of neural circuits and networks, the neurons of which are located at considerable distances from each other. There is also a special kind of local neural circuits in the cortex, formed by adjacent neurons. These neural structures are called functional cortical columns. Neuronal columns are formed by groups of neurons located one above the other perpendicular to the surface of the cortex. The belonging of neurons to the same column can be determined by the increase in their electrical activity in response to stimulation of the same receptive field. Such activity is recorded when the recording electrode is slowly moved in the cortex in a perpendicular direction. If the electrical activity of neurons located in the horizontal plane of the cortex is recorded, then an increase in their activity is noted when various receptive fields are stimulated.

The diameter of the functional column is up to 1 mm. The neurons of one functional column receive signals from the same afferent thalamocortical fiber. The neurons of adjacent columns are connected to each other by processes through which they exchange information. The presence of such interconnected functional columns in the cortex increases the reliability of perception and analysis of information coming to the cortex.

The efficiency of perception, processing and use of information by the cortex for the regulation of physiological processes is also ensured somatotopic principle of organization sensory and motor fields of the cortex. The essence of such an organization is that in a certain (projective) area of ​​the cortex, not any, but topographically outlined areas of the receptive field of the surface of the body, muscles, joints, or internal organs are represented. So, for example, in the somatosensory cortex, the surface of the human body is projected in the form of a scheme, when receptive fields of a specific area of ​​the body surface are presented at a certain point in the cortex. Efferent neurons are represented in a strict topographical way in the primary motor cortex, the activation of which causes the contraction of certain muscles of the body.

The fields of the cortex are also inherent screen operating principle. In this case, the receptor neuron sends a signal not to a single neuron or to a single point of the cortical center, but to a network or field of neurons connected by processes. The functional cells of this field (screen) are columns of neurons.

The cerebral cortex, being formed at the later stages of the evolutionary development of higher organisms, to a certain extent subordinated to itself all the underlying parts of the CNS and is able to correct their functions. At the same time, the functional activity of the cerebral cortex is determined by the influx of signals to it from the neurons of the reticular formation of the brain stem and signals from the receptive fields of the sensory systems of the body.

Functional areas of the cerebral cortex

According to the functional basis, sensory, associative and motor areas are distinguished in the cortex.

Sensory (sensitive, projection) areas of the cortex

They consist of zones containing neurons, the activation of which by afferent impulses from sensory receptors or direct exposure to stimuli causes the appearance of specific sensations. These zones are present in the occipital (fields 17-19), parietal (zeros 1-3) and temporal (fields 21-22, 41-42) areas of the cortex.

In the sensory areas of the cortex, central projection fields are distinguished, providing a subtle, clear perception of sensations of certain modalities (light, sound, touch, heat, cold) and secondary projection fields. The function of the latter is to provide an understanding of the connection of the primary sensation with other objects and phenomena of the surrounding world.

The areas of representation of receptive fields in the sensory areas of the cortex largely overlap. A feature of the nerve centers in the area of ​​secondary projection fields of the cortex is their plasticity, which is manifested by the possibility of restructuring specialization and restoring functions after damage to any of the centers. These compensatory abilities of the nerve centers are especially pronounced in childhood. At the same time, damage to the central projection fields after suffering a disease is accompanied by a gross violation of the functions of sensitivity and often the impossibility of its restoration.

visual cortex

The primary visual cortex (VI, field 17) is located on both sides of the spur groove on the medial surface of the occipital lobe of the brain. In accordance with the identification of alternating white and dark stripes on unstained sections of the visual cortex, it is also called the striate (striated) cortex. The neurons of the lateral geniculate body send visual signals to the neurons of the primary visual cortex, which receive signals from the ganglion cells of the retina. The visual cortex of each hemisphere receives visual signals from the ipsilateral and contralateral halves of the retina of both eyes, and their flow to the neurons of the cortex is organized according to the somatotopic principle. Neurons that receive visual signals from photoreceptors are topographically located in the visual cortex, similar to receptors in the retina. At the same time, the area of ​​the macula of the retina has a relatively large zone of representation in the cortex than other areas of the retina.

The neurons of the primary visual cortex are responsible for visual perception, which, based on the analysis of input signals, is manifested by their ability to detect a visual stimulus, determine its specific shape and orientation in space. In a simplified way, it is possible to imagine the sensory function of the visual cortex in solving a problem and answering the question of what constitutes a visual object.

In the analysis of other qualities of visual signals (for example, location in space, movement, connection with other events, etc.), neurons of fields 18 and 19 of the extrastriate cortex, located adjacent to zero 17, take part. Information about the signals received by the sensory visual zones of the cortex, will be transferred for further analysis and use of vision to perform other brain functions in the associative areas of the cortex and other parts of the brain.

auditory cortex

It is located in the lateral sulcus of the temporal lobe in the region of the Heschl gyrus (AI, fields 41-42). The neurons of the primary auditory cortex receive signals from the neurons of the medial geniculate bodies. The fibers of the auditory pathways that conduct sound signals to the auditory cortex are organized tonotopically, and this allows cortical neurons to receive signals from certain auditory receptor cells in the organ of Corti. The auditory cortex regulates the sensitivity of auditory cells.

In the primary auditory cortex, sound sensations are formed and the individual qualities of sounds are analyzed to answer the question of what the perceived sound is. The primary auditory cortex plays an important role in the analysis of short sounds, intervals between sound signals, rhythm, sound sequence. A more complex analysis of sounds is carried out in the associative areas of the cortex adjacent to the primary auditory. Based on the interaction of neurons in these areas of the cortex, binaural hearing is carried out, the characteristics of pitch, timbre, sound volume, sound belonging are determined, and an idea of ​​a three-dimensional sound space is formed.

vestibular cortex

It is located in the upper and middle temporal gyri (fields 21-22). Its neurons receive signals from the neurons of the vestibular nuclei of the brain stem, connected by afferent connections with the receptors of the semicircular canals of the vestibular apparatus. In the vestibular cortex, a feeling is formed about the position of the body in space and the acceleration of movements. The vestibular cortex interacts with the cerebellum (through the temporo-pontocerebellar pathway), participates in the regulation of body balance, adaptation of the posture to the implementation of purposeful movements. Based on the interaction of this area with the somatosensory and associative areas of the cortex, awareness of the body schema occurs.

Olfactory cortex

It is located in the region of the upper part of the temporal lobe (hook, zeros 34, 28). The cortex includes a number of nuclei and belongs to the structures of the limbic system. Its neurons are located in three layers and receive afferent signals from the mitral cells of the olfactory bulb, connected by afferent connections with olfactory receptor neurons. In the olfactory cortex, a primary qualitative analysis of odors is carried out and a subjective sense of smell, its intensity, and belonging is formed. Damage to the cortex leads to a decrease in the sense of smell or to the development of anosmia - loss of smell. With artificial stimulation of this area, there are sensations of various smells like hallucinations.

taste bark

It is located in the lower part of the somatosensory gyrus, directly anterior to the face projection area (field 43). Its neurons receive afferent signals from relay neurons of the thalamus, which are associated with neurons in the nucleus of the solitary tract of the medulla oblongata. The neurons of this nucleus receive signals directly from sensory neurons that form synapses on the cells of the taste buds. In the taste cortex, a primary analysis of the taste qualities of bitter, salty, sour, sweet is carried out, and on the basis of their summation, a subjective sensation of taste, its intensity, and belonging is formed.

Smell and taste signals reach the neurons of the anterior insular cortex, where, based on their integration, a new, more complex quality of sensations is formed that determines our relationship to the sources of smell or taste (for example, to food).

Somatosensory cortex

It occupies the region of the postcentral gyrus (SI, fields 1-3), including the paracentral lobule on the medial side of the hemispheres (Fig. 9.14). The somatosensory area receives sensory signals from thalamic neurons connected by spinothalamic pathways with skin receptors (tactile, temperature, pain sensitivity), proprioceptors (muscle spindles, articular bags, tendons) and interoreceptors (internal organs).

Rice. 9.14. The most important centers and areas of the cerebral cortex

Due to the intersection of afferent pathways, signaling comes to the somatosensory zone of the left hemisphere from the right side of the body, respectively, to the right hemisphere from the left side of the body. In this sensory area of ​​the cortex, all parts of the body are somatotopically represented, but the most important receptive zones of the fingers, lips, skin of the face, tongue, and larynx occupy relatively larger areas than the projections of such body surfaces as the back, front of the torso, and legs.

The location of the representation of the sensitivity of body parts along the postcentral gyrus is often called the "inverted homunculus", since the projection of the head and neck is in the lower part of the postcentral gyrus, and the projection of the caudal part of the trunk and legs is in the upper part. In this case, the sensitivity of the legs and feet is projected onto the cortex of the paracentral lobule of the medial surface of the hemispheres. Within the primary somatosensory cortex there is a certain specialization of neurons. For example, field 3 neurons receive mainly signals from muscle spindles and mechanoreceptors of the skin, field 2 - from joint receptors.

The postcentral gyrus cortex is referred to as the primary somatosensory area (SI). Its neurons send processed signals to neurons in the secondary somatosensory cortex (SII). It is located posterior to the postcentral gyrus in the parietal cortex (fields 5 and 7) and belongs to the association cortex. SII neurons do not receive direct afferent signals from thalamic neurons. They are associated with SI neurons and neurons in other areas of the cerebral cortex. This makes it possible to carry out an integral assessment of signals entering the cortex along the spinothalamic pathway with signals coming from other (visual, auditory, vestibular, etc.) sensory systems. The most important function of these fields of the parietal cortex is the perception of space and the transformation of sensory signals into motor coordinates. In the parietal cortex, a desire (intention, impulse) to carry out a motor action is formed, which is the basis for the beginning of planning for the upcoming motor activity in it.

The integration of various sensory signals is associated with the formation of various sensations addressed to different parts of the body. These sensations are used both to form mental and other responses, examples of which can be movements with the simultaneous participation of the muscles of both sides of the body (for example, moving, feeling with both hands, grasping, unidirectional movement with both hands). The functioning of this area is necessary for recognizing objects by touch and determining the spatial location of these objects.

The normal function of the somatosensory areas of the cortex is an important condition for the formation of sensations such as heat, cold, pain and their addressing to a specific part of the body.

Damage to neurons in the area of ​​the primary somatosensory cortex leads to a decrease in various types of sensitivity on the opposite side of the body, and local damage leads to a loss of sensitivity in a certain part of the body. Discriminatory sensitivity of the skin is especially vulnerable when the neurons of the primary somatosensory cortex are damaged, and the least sensitive is pain. Damage to neurons in the secondary somatosensory area of ​​the cortex may be accompanied by a violation of the ability to recognize objects by touch (tactile agnosia) and skills in using objects (apraxia).

Motor areas of the cortex

About 130 years ago, researchers, applying point stimulation to the cerebral cortex with an electric current, found that the impact on the surface of the anterior central gyrus causes contraction of the muscles of the opposite side of the body. Thus, the presence of one of the motor areas of the cerebral cortex was discovered. Subsequently, it turned out that several areas of the cerebral cortex and its other structures are related to the organization of movements, and in the areas of the motor cortex there are not only motor neurons, but also neurons that perform other functions.

primary motor cortex located in the anterior central gyrus (MI, field 4). Its neurons receive the main afferent signals from the neurons of the somatosensory cortex - fields 1, 2, 5, premotor cortex and thalamus. In addition, cerebellar neurons send signals to the MI via the ventrolateral thalamus.

Efferent fibers of the pyramidal pathway begin from the pyramidal neurons Ml. Some of the fibers of this pathway go to the motor neurons of the nuclei of the cranial nerves of the brainstem (corticobulbar tract), some to the neurons of the stem motor nuclei (red nucleus, nuclei of the reticular formation, stem nuclei associated with the cerebellum) and some to the inter- and motor neurons of the spinal cord. brain (corticospinal tract).

There is a somatotopic organization of the location of neurons in MI that control the contraction of different muscle groups of the body. The neurons that control the muscles of the legs and trunk are located in the upper parts of the gyrus and occupy a relatively small area, and the controlling muscles of the hands, especially the fingers, face, tongue and pharynx are located in the lower parts and occupy a large area. Thus, in the primary motor cortex, a relatively large area is occupied by those neural groups that control the muscles that carry out various, precise, small, finely regulated movements.

Since many Ml neurons increase electrical activity immediately before the onset of voluntary contractions, the primary motor cortex is assigned the leading role in controlling the activity of the motor nuclei of the trunk and spinal cord motoneurons and initiating voluntary, purposeful movements. Damage to the Ml field leads to muscle paresis and the impossibility of fine voluntary movements.

Includes areas of the premotor and supplementary motor cortex (MII, field 6). premotor cortex located in field 6, on the lateral surface of the brain, anterior to the primary motor cortex. Its neurons receive afferent signals through the thalamus from the occipital, somatosensory, parietal associative, prefrontal areas of the cortex and cerebellum. The signals processed in it are sent by the neurons of the cortex along the efferent fibers to the motor cortex MI, a small number - to the spinal cord and a larger number - to the red nuclei, the nuclei of the reticular formation, the basal ganglia and the cerebellum. The premotor cortex plays a major role in the programming and organization of movements under the control of vision. The cortex is involved in the organization of posture and auxiliary movements for the actions carried out by the distal muscles of the limbs. Damage to the visual cortex often causes a tendency to re-execute the initiated movement (perseveration), even if the completed movement has reached the goal.

In the lower part of the premotor cortex of the left frontal lobe, immediately anterior to the region of the primary motor cortex, in which the neurons that control the muscles of the face are represented, is located speech area, or Broca's motor center of speech. Violation of its function is accompanied by a violation of the articulation of speech, or motor aphasia.

Additional motor cortex located in the upper part of field 6. Its neurons receive afferent signals from the somatossensor, parietal and prefrontal areas of the cerebral cortex. The signals processed in it are sent by the neurons of the cortex along the efferent fibers to the primary motor cortex MI, the spinal cord, and the stem motor nuclei. The activity of the neurons of the supplementary motor cortex increases earlier than that of the neurons of the MI cortex, and mainly in connection with the implementation of complex movements. At the same time, an increase in neural activity in the additional motor cortex is not associated with movements as such; for this, it is enough to mentally imagine a model of upcoming complex movements. The supplementary motor cortex is involved in the formation of a program of upcoming complex movements and in the organization of motor reactions to the specificity of sensory stimuli.

Since the neurons of the secondary motor cortex send many axons to the MI field, it is considered to be a higher structure in the hierarchy of motor centers for organizing movements, standing above the motor centers of the MI motor cortex. The nerve centers of the secondary motor cortex can influence the activity of motor neurons in the spinal cord in two ways: directly through the corticospinal pathway and through the MI field. Therefore, they are sometimes called supramotor fields, the function of which is to instruct the centers of the MI field.

From clinical observations, it is known that maintaining the normal function of the secondary motor cortex is important for the implementation of precise hand movements, and especially for the performance of rhythmic movements. So, for example, if they are damaged, the pianist ceases to feel the rhythm and maintain the interval. The ability to perform opposite hand movements (manipulation with both hands) is impaired.

With simultaneous damage to the motor areas MI and MII of the cortex, the ability to fine coordinated movements is lost. Point irritations in these areas of the motor zone are accompanied by activation not of individual muscles, but of a whole group of muscles that cause directed movement in the joints. These observations led to the conclusion that the motor cortex is represented not so much by muscles as by movements.

It is located in the region of field 8. Its neurons receive the main afferent signals from the occipital visual, parietal associative cortex, superior colliculi of the quadrigemina. The processed signals are transmitted via efferent fibers to the premotor cortex, superior colliculus, and stem motor centers. The cortex plays a decisive role in the organization of movements under the control of vision and is directly involved in the initiation and control of eye and head movements.

The mechanisms that implement the transformation of the idea of ​​movement into a specific motor program, into bursts of impulses sent to certain muscle groups, remain insufficiently understood. It is believed that the idea of ​​movement is formed due to the functions of the associative and other areas of the cortex, interacting with many brain structures.

Information about the intention of movement is transmitted to the motor areas of the frontal cortex. The motor cortex, through descending pathways, activates systems that ensure the development and use of new motor programs or the use of old ones that have already been worked out in practice and stored in memory. An integral part of these systems are the basal ganglia and the cerebellum (see their functions above). Movement programs developed with the participation of the cerebellum and basal ganglia are transmitted through the thalamus to the motor areas and, above all, to the primary motor cortex. This area directly initiates the execution of movements, connecting certain muscles to it and providing a sequence of changes in their contraction and relaxation. Cortical commands are transmitted to the motor centers of the brain stem, spinal motor neurons and motor neurons of the cranial nerve nuclei. In the implementation of movements, motor neurons play the role of the final path through which motor commands are transmitted directly to the muscles. Features of signal transmission from the cortex to the motor centers of the stem and spinal cord are described in the chapter on the central nervous system (brain stem, spinal cord).

Association areas of the cortex

In humans, the associative areas of the cortex occupy about 50% of the area of ​​the entire cerebral cortex. They are located in the areas between the sensory and motor areas of the cortex. Associative areas do not have clear boundaries with secondary sensory areas, both in terms of morphological and functional features. Allocate parietal, temporal and frontal associative areas of the cerebral cortex.

Parietal association area of ​​the cortex. It is located in fields 5 and 7 of the upper and lower parietal lobes of the brain. The area borders in front of the somatosensory cortex, behind - with the visual and auditory cortex. Visual, sound, tactile, proprioceptive, pain, signals from the memory apparatus and other signals can enter and activate the neurons of the parietal associative area. Some neurons are polysensory and can increase their activity when they receive somatosensory and visual signals. However, the degree of increase in the activity of neurons in the associative cortex in response to afferent signals depends on the current motivation, the attention of the subject, and information retrieved from memory. It remains insignificant if the signal coming from the sensory areas of the brain is indifferent to the subject, and increases significantly if it coincided with the existing motivation and attracted his attention. For example, when a monkey is presented with a banana, the activity of neurons in the associative parietal cortex remains low if the animal is full, and vice versa, activity increases sharply in hungry animals that like bananas.

The neurons of the parietal association cortex are connected by efferent connections with the neurons of the prefrontal, premotor, motor areas of the frontal lobe and cingulate gyrus. Based on experimental and clinical observations, it is generally accepted that one of the functions of the field 5 cortex is the use of somatosensory information for the implementation of purposeful voluntary movements and manipulation of objects. The function of the field 7 cortex is the integration of visual and somatosensory signals to coordinate eye movements and visually guided hand movements.

Violation of these functions of the parietal associative cortex in case of damage to its connections with the cortex of the frontal lobe or disease of the frontal lobe itself, explains the symptoms of the consequences of diseases localized in the region of the parietal associative cortex. They can be manifested by difficulty in understanding the semantic content of signals (agnosia), an example of which may be the loss of the ability to recognize the shape and spatial location of an object. The processes of transformation of sensory signals into adequate motor actions may be disturbed. In the latter case, the patient loses skills in the practical use of well-known tools and objects (apraxia), and he may develop an inability to perform visually guided movements (for example, moving a hand in the direction of an object).

Frontal association area of ​​the cortex. It is located in the prefrontal cortex, which is part of the cortex of the frontal lobe, localized anterior to fields 6 and 8. The neurons of the frontal association cortex receive processed sensory signals via afferent connections from the neurons of the cortex of the occipital, parietal, temporal lobes of the brain and from the neurons of the cingulate gyrus. The frontal associative cortex receives signals about the current motivational and emotional states from the nuclei of the thalamus, limbic and other brain structures. In addition, the frontal cortex can operate with abstract, virtual signals. The associative frontal cortex sends efferent signals back to the brain structures from which they were received, to the motor areas of the frontal cortex, the caudate nucleus of the basal ganglia, and the hypothalamus.

This area of ​​the cortex plays a primary role in the formation of higher mental functions of a person. It provides the formation of target settings and programs of conscious behavioral reactions, recognition and semantic evaluation of objects and phenomena, speech understanding, logical thinking. After extensive damage to the frontal cortex, patients may develop apathy, a decrease in the emotional background, a critical attitude towards their own actions and the actions of others, complacency, a violation of the possibility of using past experience to change behavior. The behavior of patients can become unpredictable and inadequate.

Temporal association area of ​​the cortex. It is located in fields 20, 21, 22. Cortical neurons receive sensory signals from neurons in the auditory, extrastriate visual and prefrontal cortex, hippocampus and amygdala.

After a bilateral disease of the temporal associative areas with involvement of the hippocampus or connections with it in the pathological process, patients may develop severe memory impairment, emotional behavior, inability to concentrate (absent-mindedness). Some people with damage to the lower temporal region, where the center of face recognition is supposedly located, may develop visual agnosia - the inability to recognize the faces of familiar people, objects, while maintaining vision.

On the border of the temporal, visual and parietal areas of the cortex in the lower parietal and posterior part of the temporal lobe, there is an associative area of ​​the cortex, called sensory center of speech, or Wernicke's center. After its damage, a violation of the function of understanding speech develops while the speech motor function is preserved.

Modern scientists know for certain that thanks to the functioning of the brain, such abilities as awareness of signals received from the external environment, mental activity, and memorization of thinking are possible.

The ability of a person to be aware of his own relationships with other people is directly related to the process of excitation of neural networks. And we are talking about those neural networks that are located in the cortex. It is the structural basis of consciousness and intellect.

In this article, we will consider how the cerebral cortex is arranged, the zones of the cerebral cortex will be described in detail.

neocortex

The cortex includes about fourteen billion neurons. It is thanks to them that the functioning of the main zones is carried out. The vast majority of neurons, up to ninety percent, form the neocortex. It is part of the somatic NS and its highest integrative department. The most important functions of the cerebral cortex are the perception, processing, interpretation of information that a person receives with the help of various sense organs.

In addition, the neocortex controls the complex movements of the human body's muscle system. It contains centers that take part in the process of speech, memory storage, abstract thinking. Most of the processes that take place in it form the neurophysical basis of human consciousness.

What parts of the cerebral cortex are made up of? The areas of the cerebral cortex will be discussed below.

paleocortex

It is another large and important section of the cortex. Compared to the neocortex, the paleocortex has a simpler structure. The processes that take place here are rarely reflected in consciousness. In this section of the cortex, the higher vegetative centers are localized.

Communication of the cortical layer with other parts of the brain

It is important to consider the connection that exists between the underlying parts of the brain and the cerebral cortex, for example, with the thalamus, bridge, middle bridge, basal ganglia. This connection is carried out with the help of large bundles of fibers that form the inner capsule. The fiber bundles are represented by wide layers, which are composed of white matter. They contain a huge number of nerve fibers. Some of these fibers provide transmission of nerve signals to the cortex. The rest of the bundles transmits nerve impulses to the nerve centers located below.

How is the cerebral cortex structured? The areas of the cerebral cortex will be presented below.

The structure of the bark

The largest part of the brain is its cortex. Moreover, cortical zones are only one type of parts distinguished in the cortex. In addition, the cortex is divided into two hemispheres - right and left. Between themselves, the hemispheres are connected by bundles of white matter, forming the corpus callosum. Its function is to ensure the coordination of the activities of both hemispheres.

Classification of areas of the cerebral cortex according to their location

Despite the fact that the bark has a huge number of folds, in general, the location of its individual convolutions and furrows is constant. The main ones are a guideline in the selection of areas of the cortex. These zones (lobes) include - occipital, temporal, frontal, parietal. Although they are classified by location, each of them has its own specific functions.

auditory area of ​​the cerebral cortex

For example, the temporal zone is the center in which the cortical section of the hearing analyzer is located. If there is damage to this section of the cortex, deafness may occur. In addition, Wernicke's speech center is located in the auditory zone. If it is damaged, then the person loses the ability to perceive oral speech. The person perceives it as simple noise. Also in the temporal lobe there are neuronal centers that belong to the vestibular apparatus. If they are damaged, the sense of balance is disturbed.

Speech areas of the cerebral cortex

The speech zones are concentrated in the frontal lobe of the cortex. The speech motor center is also located here. If it is damaged in the right hemisphere, then the person loses the ability to change the timbre and intonation of his own speech, which becomes monotonous. If the damage to the speech center occurred in the left hemisphere, then articulation, the ability to articulate speech and singing disappear. What else is the cerebral cortex made of? The areas of the cerebral cortex have different functions.

visual zones

In the occipital lobe is the visual zone, in which there is a center that responds to our vision as such. The perception of the surrounding world occurs precisely with this part of the brain, and not with the eyes. It is the occipital cortex that is responsible for vision, and damage to it can lead to partial or complete loss of vision. The visual area of ​​the cerebral cortex is considered. What's next?

The parietal lobe also has its own specific functions. It is this zone that is responsible for the ability to analyze information that relates to tactile, temperature and pain sensitivity. If there is damage to the parietal region, the reflexes of the brain are disturbed. A person cannot recognize objects by touch.

Motor zone

Let's talk about the motor zone separately. It should be noted that this area of ​​the cortex does not correlate in any way with the lobes discussed above. It is part of the cortex containing direct connections to motor neurons in the spinal cord. This name is given to neurons that directly control the activity of the muscles of the body.

The main motor area of ​​the cerebral cortex is located in the gyrus, which is called the precentral. This gyrus is a mirror image of the sensory area in many ways. Between them there is a contralateral innervation. In other words, the innervation is directed to the muscles that are located on the other side of the body. An exception is the facial area, which is characterized by bilateral muscle control located on the jaw, lower face.

Slightly below the main motor zone is an additional zone. Scientists believe that it has independent functions that are associated with the process of outputting motor impulses. The additional motor zone was also studied by specialists. Experiments that were performed on animals show that stimulation of this zone provokes the occurrence of motor reactions. A feature is that such reactions occur even if the main motor zone was isolated or completely destroyed. It is also involved in planning movements and motivating speech in the dominant hemisphere. Scientists believe that if the additional motor is damaged, dynamic aphasia can occur. The reflexes of the brain suffer.

Classification according to the structure and functions of the cerebral cortex

Physiological experiments and clinical trials, which were carried out at the end of the nineteenth century, made it possible to establish the boundaries between areas on which different receptor surfaces are projected. Among them, there are sense organs that are directed to the outside world (skin sensitivity, hearing, vision), receptors embedded directly in the organs of movement (motor or kinetic analyzers).

The areas of the cortex, in which various analyzers are located, can be classified according to their structure and functions. So, there are three of them. These include: primary, secondary, tertiary areas of the cerebral cortex. The development of the embryo involves the laying of only primary zones, characterized by simple cytoarchitectonics. Next comes the development of secondary, tertiary develop in the very last turn. Tertiary zones are characterized by the most complex structure. Let's consider each of them in a little more detail.

Center fields

Over the years of clinical research, scientists have managed to accumulate significant experience. Observations made it possible to establish, for example, that damage to various fields, as part of the cortical sections of different analyzers, may not be equally reflected in the overall clinical picture. If we consider all these fields, then among them one can be distinguished, which occupies a central position in the nuclear zone. Such a field is called the central or primary. It is located simultaneously in the visual zone, in the kinesthetic zone, in the auditory zone. Damage to the primary field entails very serious consequences. A person cannot perceive and carry out the most subtle differentiation of stimuli that affect the corresponding analyzers. How else are areas of the cerebral cortex classified?

Primary Zones

In the primary zones, there is a complex of neurons that is most predisposed to providing bilateral connections between the cortical and subcortical zones. It is this complex that connects the cerebral cortex with a variety of sensory organs in the most direct and shortest way. In this regard, these zones have the ability to very detailed identification of stimuli.

An important common feature of the functional and structural organization of the primary areas is that they all have a clear somatic projection. This means that individual peripheral points, for example, skin surfaces, retina, skeletal muscles, cochlea of ​​the inner ear, have their own projection into strictly limited, corresponding points that are located in the primary zones of the cortex of the corresponding analyzers. In this regard, they were given the name of the projection zones of the cerebral cortex.

Secondary zones

In another way, these zones are called peripheral. This name was not given to them by chance. They are located in the peripheral sections of the cortex. Secondary zones differ from the central (primary) zones in their neuronal organization, physiological manifestations, and architectonic features.

Let's try to figure out what effects occur if the secondary zones are affected by an electrical stimulus or if they are damaged. The effects that arise mainly concern the most complex types of processes in the psyche. In the event that secondary zones are damaged, elementary sensations remain relatively intact. Basically, there are violations in the ability to correctly reflect the mutual relationships and entire complexes of elements that make up the various objects that we perceive. For example, if the secondary zones of the visual and auditory cortex were damaged, then one can observe the occurrence of auditory and visual hallucinations that unfold in a certain temporal and spatial sequence.

Secondary areas are of significant importance in the implementation of the mutual connections of stimuli that are distinguished using the primary areas of the cortex. In addition, they play a significant role in the integration of functions that are carried out by the nuclear fields of different analyzers as a result of combining into complex complexes of receptions.

Thus, secondary zones are of particular importance for the implementation of mental processes in more complex forms that require coordination and are associated with a detailed analysis of the relationships between objective stimuli. During this process, specific connections are established, which are called associative. Afferent impulses entering the cortex from the receptors of various external sense organs reach the secondary fields through many additional switches in the associative nucleus of the thalamus, which is also called the thalamic thalamus. Afferent impulses following in the primary zones, in contrast to impulses, follow in the secondary zones, reach them in a way that is shorter. It is implemented by means of a relay-core, in the thalamus.

We figured out what the cerebral cortex is responsible for.

What is the thalamus?

From the thalamic nuclei, fibers approach each lobe of the cerebral hemispheres. The thalamus is a visual mound located in the central part of the anterior part of the brain, consists of a large number of nuclei, each of which transmits an impulse to certain areas of the cortex.

All signals that enter the cortex (the only exception is olfactory ones) pass through the relay and integrative nuclei of the thalamus opticus. From the nuclei of the thalamus, the fibers are sent to the sensory areas. Taste and somatosensory zones are located in the parietal lobe, auditory sensory zone - in the temporal lobe, visual - in the occipital lobe.

Impulses come to them, respectively, from the ventrobasal complexes, medial and lateral nuclei. Motor zones are associated with the ventral and ventrolateral nuclei of the thalamus.

EEG desynchronization

What happens if a very strong stimulus acts on a person who is in a state of complete rest? Naturally, a person will completely concentrate on this stimulus. The transition of mental activity, which is carried out from a state of rest to a state of activity, is reflected on the EEG by a beta rhythm, which replaces the alpha rhythm. The fluctuations become more frequent. This transition is called EEG desynchronization; it appears as a result of sensory excitation entering the cortex from nonspecific nuclei located in the thalamus.

activating reticular system

Diffuse nervous system is made up of non-specific nuclei. This system is located in the medial parts of the thalamus. It is the anterior part of the activating reticular system that regulates the excitability of the cortex. A variety of sensory signals can activate this system. Sensory signals can be both visual and olfactory, somatosensory, vestibular, auditory. The reticular activating system is a channel that transmits signal data to the surface layer of the cortex through non-specific nuclei located in the thalamus. The arousal of ARS is necessary for a person to be able to maintain a state of wakefulness. If disturbances occur in this system, then coma-like sleep-like states can be observed.

Tertiary zones

There are functional relationships between the analyzers of the cerebral cortex, which have an even more complex structure than the one described above. In the process of growth, the fields of the analyzers overlap. Such overlap zones, which are formed at the ends of the analyzers, are called tertiary zones. They are the most complex types of combining the activities of the auditory, visual, skin-kinesthetic analyzers. The tertiary zones are located outside the boundaries of the analyzers' own zones. In this regard, damage to them does not have a pronounced effect.

Tertiary zones are special cortical areas in which scattered elements of different analyzers are collected. They occupy a very vast territory, which is divided into regions.

The upper parietal region integrates the movements of the whole body with the visual analyzer, and forms a scheme of bodies. The lower parietal region combines generalized forms of signaling, which are associated with differentiated subject and speech actions.

No less important is the temporo-parieto-occipital region. She is responsible for the complicated integration of auditory and visual analyzers with oral and written speech.

It should be noted that in comparison with the first two zones, the tertiary ones are characterized by the most complex chains of interaction.

Based on all the above material, we can conclude that the primary, secondary, tertiary zones of the human cortex are highly specialized. Separately, it is worth emphasizing the fact that all three cortical zones that we considered, in a normally functioning brain, together with the systems of connections and formations of the subcortical location, function as a single differentiated whole.

We examined in detail the zones and sections of the cerebral cortex.

The reticular formation of the brain stem occupies a central position in the medulla oblongata, pons varolii, midbrain and diencephalon.

The neurons of the reticular formation do not have direct contacts with the body's receptors. When the receptors are excited, nerve impulses arrive at the reticular formation along the collaterals of the fibers of the autonomic and somatic nervous system.

Physiological role. The reticular formation of the brain stem has an ascending effect on the cells of the cerebral cortex and a descending effect on the motor neurons of the spinal cord. Both of these influences of the reticular formation can be activating or inhibitory.

Afferent impulses to the cerebral cortex come in two ways: specific and nonspecific. specific neural pathway necessarily passes through the visual tubercles and carries nerve impulses to certain areas of the cerebral cortex, as a result, any specific activity is carried out. For example, when the photoreceptors of the eyes are stimulated, impulses through the visual tubercles enter the occipital region of the cerebral cortex and visual sensations arise in a person.

Nonspecific neural pathway necessarily passes through the neurons of the reticular formation of the brain stem. Impulses to the reticular formation come through the collaterals of a specific nerve pathway. Due to numerous synapses on the same neuron of the reticular formation, impulses of different values ​​(light, sound, etc.) can converge (converge), while they lose their specificity. From the neurons of the reticular formation, these impulses do not arrive in any particular area of ​​the cerebral cortex, but spread like a fan through its cells, increasing their excitability and thereby facilitating the performance of a specific function.

In experiments on cats with electrodes implanted in the region of the reticular formation of the brainstem, it was shown that stimulation of its neurons causes the awakening of a sleeping animal. With the destruction of the reticular formation, the animal falls into a long sleepy state. These data indicate the important role of the reticular formation in the regulation of sleep and wakefulness. The reticular formation not only affects the cerebral cortex, but also sends inhibitory and excitatory impulses to the spinal cord to its motor neurons. Due to this, it is involved in the regulation of skeletal muscle tone.

In the spinal cord, as already mentioned, there are also neurons of the reticular formation. It is believed that they maintain a high level of activity of neurons in the spinal cord. The functional state of the reticular formation itself is regulated by the cerebral cortex.

Cerebellum

Features of the structure of the cerebellum. Connections of the cerebellum with other parts of the central nervous system. The cerebellum is an unpaired formation; it is located behind the medulla oblongata and the pons, borders on the quadruples, is covered from above by the occipital lobes of the cerebral hemispheres, In the cerebellum, the middle part is distinguished - worm and located on the sides of it two hemisphere. The surface of the cerebellum consists of gray matter called the cortex, which includes the bodies of nerve cells. Inside the cerebellum is white matter, representing the processes of these neurons.

The cerebellum has extensive connections with various parts of the central nervous system due to three pairs of legs. lower legs connect the cerebellum to the spinal cord and medulla oblongata medium- with the pons and through it with the motor area of ​​the cerebral cortex, upper with midbrain and hypothalamus.

The functions of the cerebellum were studied in animals in which the cerebellum was removed partially or completely, as well as by recording its bioelectrical activity at rest and during stimulation.

When half of the cerebellum is removed, an increase in the tone of the extensor muscles is noted, therefore, the limbs of the animal are extended, the trunk is bent and the head is tilted to the operated side, and sometimes rocking movements of the head are observed. Often the movements are made in a circle in the operated direction (“manege movements”). Gradually, the marked violations are smoothed out, but some awkwardness of movements remains.

When the entire cerebellum is removed, more pronounced movement disorders occur. In the first days after the operation, the animal lies motionless with its head thrown back and elongated limbs. Gradually, the tone of the extensor muscles weakens, trembling of the muscles appears, especially the cervical ones. In the future, motor functions are partially restored. However, until the end of life, the animal remains a motor invalid: when walking, such animals spread their limbs wide, raise their paws high, i.e., they have impaired coordination of movements.

Movement disorders during the removal of the cerebellum were described by the famous Italian physiologist Luciani. The main ones are: aton and I - the disappearance or weakening of muscle tone; asthen and I - a decrease in the strength of muscle contractions. Such an animal is characterized by rapidly onset muscle fatigue; a stasis - loss of the ability to continuous tetanic contractions. In animals, trembling movements of the limbs and head are observed. The dog after removal of the cerebellum cannot immediately raise its paws, the animal makes a series of oscillatory movements with its paw before lifting it. If you put such a dog, then its body and head sway all the time from side to side.

As a result of atony, asthenia and astasia, the animal's coordination of movements is disturbed: a shaky gait, sweeping, awkward, inaccurate movements are noted. The whole complex of motor disorders in the lesion of the cerebellum is called cerebellar ataxia.

Similar disorders are observed in humans with damage to the cerebellum.

Some time after the removal of the cerebellum, as already mentioned, all movement disorders are gradually smoothed out. If the motor area of ​​the cerebral cortex is removed from such animals, then the motor disturbances increase again. Consequently, compensation (restoration) of movement disorders in case of damage to the cerebellum is carried out with the participation of the cerebral cortex, its motor area.

The studies of L. A. Orbeli showed that when the cerebellum is removed, not only a drop in muscle tone (atony), but also its incorrect distribution (dystonia) is observed. L. L. Orbeli found that the cerebellum also affects the state of the receptor apparatus, as well as autonomic processes. The cerebellum has an adaptive-trophic effect on all parts of the brain through the sympathetic nervous system, it regulates the metabolism in the brain and thereby contributes to the adaptation of the nervous system to changing conditions of existence.

Thus, the main functions of the cerebellum are the coordination of movements, the normal distribution of muscle tone, and the regulation of autonomic functions. The cerebellum realizes its influence through the nuclear formations of the middle and medulla oblongata, through the motor neurons of the spinal cord. A large role in this influence belongs to the bilateral connection of the cerebellum with the motor area of ​​the cerebral cortex and the reticular formation of the brain stem.

Structural features of the cerebral cortex.

The cerebral cortex is phylogenetically the highest and youngest part of the central nervous system.

The cerebral cortex consists of nerve cells, their processes and neuroglia. In an adult, the thickness of the cortex in most areas is about 3 mm. The area of ​​the cerebral cortex due to numerous folds and furrows is 2500 cm 2. Most areas of the cerebral cortex are characterized by a six-layer arrangement of neurons. The cerebral cortex consists of 14-17 billion cells. The cellular structures of the cerebral cortex are represented pyramidal,spindle and stellate neurons.

stellate cells perform mainly an afferent function. Pyramidal and fusiformcells are predominantly efferent neurons.

In the cerebral cortex there are highly specialized nerve cells that receive afferent impulses from certain receptors (for example, from visual, auditory, tactile, etc.). There are also neurons that are excited by nerve impulses coming from different receptors in the body. These are the so-called polysensory neurons.

The processes of the nerve cells of the cerebral cortex connect its various sections to each other or establish contacts between the cerebral cortex and the underlying sections of the central nervous system. The processes of nerve cells that connect different parts of the same hemisphere are called associative, connecting most often the same parts of the two hemispheres - commissural and providing contacts of the cerebral cortex with other parts of the central nervous system and through them with all organs and tissues of the body - conductive(centrifugal). A diagram of these paths is shown in the figure.

Scheme of the course of nerve fibers in the cerebral hemispheres.

1 - short associative fibers; 2 - long associative fibers; 3 - commissural fibers; 4 - centrifugal fibers.

Neuroglia cells perform a number of important functions: they are a supporting tissue, participate in the metabolism of the brain, regulate blood flow inside the brain, secrete a neurosecretion that regulates the excitability of neurons in the cerebral cortex.

Functions of the cerebral cortex.

1) The cerebral cortex carries out the interaction of the organism with the environment due to unconditioned and conditioned reflexes;

2) it is the basis of the higher nervous activity (behavior) of the organism;

3) due to the activity of the cerebral cortex, higher mental functions are carried out: thinking and consciousness;

4) the cerebral cortex regulates and integrates the work of all internal organs and regulates such intimate processes as metabolism.

Thus, with the appearance of the cerebral cortex, it begins to control all the processes occurring in the body, as well as all human activities, i.e., corticolization of functions occurs. IP Pavlov, characterizing the importance of the cerebral cortex, pointed out that it is the manager and distributor of all the activities of the animal and human organism.

Functional significance of various areas of the cortex brain . Localization of functions in the cerebral cortex brain . The role of individual areas of the cerebral cortex was first studied in 1870 by the German researchers Fritsch and Gitzig. They showed that stimulation of various parts of the anterior central gyrus and the frontal lobes proper causes contraction of certain muscle groups on the side opposite to the stimulation. Subsequently, the functional ambiguity of various areas of the cortex was revealed. It was found that the temporal lobes of the cerebral cortex are associated with auditory functions, the occipital lobes with visual functions, and so on. These studies led to the conclusion that different parts of the cerebral cortex are in charge of certain functions. The doctrine of the localization of functions in the cerebral cortex was created.

According to modern concepts, there are three types of zones of the cerebral cortex: primary projection zones, secondary and tertiary (associative).

Primary projection zones- these are the central sections of the analyzer cores. They contain highly differentiated and specialized nerve cells, which receive impulses from certain receptors (visual, auditory, olfactory, etc.). In these zones, a subtle analysis of afferent impulses of various meanings takes place. The defeat of these areas leads to disorders of sensory or motor functions.

Secondary zones- peripheral parts of the analyzer nuclei. Here, further processing of information takes place, connections are established between stimuli of different nature. When the secondary zones are affected, complex perceptual disorders occur.

Tertiary zones (associative) . The neurons of these zones can be excited under the influence of impulses coming from receptors of various values ​​(from hearing receptors, photoreceptors, skin receptors, etc.). These are the so-called polysensory neurons, due to which connections are established between various analyzers. Associative zones receive processed information from the primary and secondary zones of the cerebral cortex. Tertiary zones play an important role in the formation of conditioned reflexes; they provide complex forms of cognition of the surrounding reality.

Significance of different areas of the cerebral cortex . Sensory and motor areas in the cerebral cortex

Sensory areas of the cortex . (projective cortex, cortical sections of analyzers). These are zones into which sensory stimuli are projected. They are located mainly in the parietal, temporal and occipital lobes. Afferent pathways in the sensory cortex come mainly from the relay sensory nuclei of the thalamus - ventral posterior, lateral and medial. The sensory areas of the cortex are formed by the projection and associative zones of the main analyzers.

Area of ​​skin reception(the brain end of the skin analyzer) is represented mainly by the posterior central gyrus. The cells of this area perceive impulses from tactile, pain and temperature receptors of the skin. The projection of skin sensitivity within the posterior central gyrus is similar to that for the motor zone. The upper portions of the posterior central gyrus are associated with the receptors of the skin of the lower extremities, the middle portions with the receptors of the trunk and hands, and the lower portions with the receptors of the skin of the head and face. Irritation of this area in a person during neurosurgical operations causes sensations of touch, tingling, numbness, while pronounced pain is never observed.

Area of ​​visual reception(the cerebral end of the visual analyzer) is located in the occipital lobes of the cerebral cortex of both hemispheres. This area should be considered as a projection of the retina.

Area of ​​auditory reception(the cerebral end of the auditory analyzer) is localized in the temporal lobes of the cerebral cortex. This is where nerve impulses come from receptors in the cochlea of ​​the inner ear. If this zone is damaged, musical and verbal deafness may occur, when a person hears, but does not understand the meaning of words; Bilateral damage to the auditory region leads to complete deafness.

The area of ​​taste reception(the cerebral end of the taste analyzer) is located in the lower lobes of the central gyrus. This area receives nerve impulses from the taste buds of the oral mucosa.

Olfactory reception area(the cerebral end of the olfactory analyzer) is located in the anterior part of the piriform lobe of the cerebral cortex. This is where nerve impulses come from the olfactory receptors of the nasal mucosa.

In the cerebral cortex, several zones in charge of the function of speech(brain end of the motor speech analyzer). In the frontal region of the left hemisphere (in right-handed people) is the motor center of speech (Broca's center). With his defeat, speech is difficult or even impossible. In the temporal region is the sensory center of speech (Wernicke's center). Damage to this area leads to speech perception disorders: the patient does not understand the meaning of words, although the ability to pronounce words is preserved. In the occipital lobe of the cerebral cortex there are zones that provide the perception of written (visual) speech. With the defeat of these areas, the patient does not understand what is written.

IN parietal cortex brain ends of the analyzers were not found in the cerebral hemispheres, it is referred to the associative zones. Among the nerve cells of the parietal region, a large number of polysensory neurons were found, which contribute to the establishment of connections between various analyzers and play an important role in the formation of reflex arcs of conditioned reflexes.

motor areas of the cortex The idea of ​​the role of the motor cortex is twofold. On the one hand, it was shown that electrical stimulation of certain cortical zones in animals causes movement of the limbs of the opposite side of the body, which indicated that the cortex is directly involved in the implementation of motor functions. At the same time, it is recognized that the motor area is an analyzer, i.e. represents the cortical section of the motor analyzer.

The brain section of the motor analyzer is represented by the anterior central gyrus and the parts of the frontal region located near it. When it is irritated, various contractions of the skeletal muscles occur on the opposite side. Correspondence between certain zones of the anterior central gyrus and skeletal muscles has been established. In the upper parts of this zone, the muscles of the legs are projected, in the middle - the torso, in the lower - the head.

Of particular interest is the frontal region itself, which reaches its greatest development in humans. When the frontal areas are affected in a person, complex motor functions are disturbed that ensure labor activity and speech, as well as adaptive, behavioral reactions of the body.

Any functional area of ​​the cerebral cortex is in both anatomical and functional contact with other areas of the cerebral cortex, with subcortical nuclei, with formations of the diencephalon and reticular formation, which ensures the perfection of their functions.

1. Structural and functional features of the CNS in the antenatal period.

In the fetus, the number of CNS neurons reaches a maximum by the 20-24th week and remains in the postnatal period without a sharp decrease until old age. Neurons are small in size and the total area of ​​the synaptic membrane.

Axons develop before dendrites, processes of neurons intensively grow and branch. There is an increase in the length, diameter and myelination of axons towards the end of the antenatal period.

Phylogenetically old pathways are myelinated earlier than phylogenetically new ones; for example, vestibulospinal tracts from the 4th month of intrauterine development, rubrospinal tracts from the 5th-8th month, pyramidal tracts after birth.

Na- and K-channels are evenly distributed in the membrane of myelin and non-myelin fibers.

Excitability, conductivity, lability of nerve fibers is much lower than in adults.

The synthesis of most mediators begins during fetal development. Gamma-aminobutyric acid in the antenatal period is an excitatory mediator and, through the Ca2 mechanism, has morphogenic effects - it accelerates the growth of axons and dendrites, synaptogenesis, and the expression of pithoreceptors.

By the time of birth, the process of differentiation of neurons in the nuclei of the medulla oblongata and midbrain, the bridge, ends.

There is structural and functional immaturity of glial cells.

2. Features of the CNS in the neonatal period.

> The degree of myelination of nerve fibers increases, their number is 1/3 of the level of an adult organism (for example, the rubrospinal path is fully myelinated).

> The permeability of cell membranes for ions decreases. Neurons have a lower MP amplitude - about 50 mV (in adults, about 70 mV).

> There are fewer synapses on neurons than in adults, the neuron membrane has receptors for synthesized mediators (acetylcholine, GAM K, serotonin, norepinephrine to dopamine). The content of mediators in the neurons of the brain of newborns is low and amounts to 10-50% of mediators in adults.

> The development of the spiny apparatus of neurons and axospinous synapses is noted; EPSP and IPSP have a longer duration and lower amplitude than in adults. The number of inhibitory synapses on neurons is less than in adults.

> Increased excitability of cortical neurons.

> Disappears (more precisely, sharply decreases) mitotic activity and the possibility of regeneration of neurons. Proliferation and functional maturation of gliocytes continues.

Z. Features of the central nervous system in infancy.

CNS maturation progresses rapidly. The most intense myelination of CNS neurons occurs at the end of the first year after birth (for example, myelination of the nerve fibers of the cerebellar hemispheres is completed by 6 months).

The rate of conduction of excitation along axons increases.

There is a decrease in the duration of AP of neurons, the absolute and relative refractory phases are shortened (the duration of absolute refractoriness is 5–8 ms, relative 40–60 ms in early postnatal ontogenesis, in adults, respectively, 0.5–2.0 and 2–10 ms).

The blood supply to the brain in children is relatively greater than in adults.

4. Features of the development of the central nervous system in other age periods.

1) Structural and functional changes in nerve fibers:

An increase in the diameters of axial cylinders (by 4-9 years). Myelination in all peripheral nerve fibers is close to completion by 9 years, and pyramidal tracts are completed by 4 years;

The ion channels are concentrated in the region of nodes of Ranvier, the distance between the nodes increases. Continuous conduction of excitation is replaced by saltatory, the speed of its conduction after 5-9 years is almost the same as the speed in adults (50-70 m/s);

There is a low lability of nerve fibers in children of the first years of life; with age, it increases (in children 5-9 years old it approaches the norm for adults - 300-1,000 impulses).

2) Structural and functional changes in synapses:

Significant maturation of nerve endings (neuromuscular synapses) occurs by 7-8 years;

The terminal ramifications of the axon and the total area of ​​its endings increase.

Profile material for students of the pediatric faculty

1. Development of the brain in the postnatal period.

In the postnatal period, the leading role in the development of the brain is played by flows of afferent impulses through various sensory systems (the role of an information-enriched external environment). The absence of these external signals, especially during critical periods, can lead to slow maturation, underdevelopment of function, or even its absence.

The critical period in postnatal development is characterized by intense morphological and functional maturation of the brain and the peak of the formation of NEW connections between neurons.

The general regularity of the development of the human brain is the heterochrony of maturation: fvlogetically older sections develop earlier than younger ones.

The medulla oblongata of a newborn is functionally more developed than other departments: ALMOST all of its centers are active - respiration, regulation of the heart and blood vessels, sucking, swallowing, coughing, sneezing, the chewing center begins to function somewhat later In the regulation of muscle tone, the activity of the vestibular nuclei is reduced (reduced extensor tone) By the age of 6, these Centers complete the differentiation of neurons, myelination of fibers, and the coordination activity of the Centers improves.

The midbrain in newborns is functionally less mature. For example, the orienting reflex and the activity of the centers that control the movement of the eyes and THEM are carried out in infancy. The function of the Substance Black as part of the striopallidary system reaches perfection by the age of 7.

The cerebellum in a newborn is structurally and functionally underdeveloped during infancy, its increased growth and differentiation of neurons occurs, and the connections of the cerebellum with other motor centers increase. Functional maturation of the cerebellum generally begins at age 7 and is completed by age 16.

Maturation of the diencephalon includes the development of sensory nuclei of the thalamus and centers of the hypothalamus

The function of the sensory nuclei of the thalamus is already carried out in the Newborn, which allows the Child to distinguish between taste, temperature, tactile and pain sensations. The functions of the nonspecific nuclei of the thalamus and the ascending activating reticular formation of the brain stem in the first months of life are poorly developed, which leads to a short time of his wakefulness during the day. The nuclei of the thalamus finally develop functionally by the age of 14.

The centers of the hypothalamus in a newborn are poorly developed, which leads to imperfection in the processes of thermoregulation, regulation of water-electrolyte and other types of metabolism, and the need-motivational sphere. Most of the hypothalamic centers are functionally mature by 4 years. The most late (by the age of 16) the sexual hypothalamic centers begin to function.

By the time of birth, the basal nuclei have a different degree of functional activity. The phylogenetically older structure, the globus pallidus, is functionally well developed, while the function of the striatum manifests itself by the end of 1 year. In this regard, the movements of newborns and infants are generalized, poorly coordinated. As the striopalidar system develops, the child performs more and more precise and coordinated movements, creates motor programs of voluntary movements. Structural and functional maturation of the basal nuclei is completed by the age of 7.

The cerebral cortex in early ontogenesis matures later in structural and functional terms. The motor and sensory cortex develops the earliest, the maturation of which ends at the 3rd year of life (auditory and visual cortex somewhat later). The critical period in the development of the associative cortex begins at the age of 7 years and continues until the pubertal period. At the same time, cortical-subcortical interconnections are intensively formed. The cerebral cortex provides the corticalization of body functions, the regulation of voluntary movements, the creation of motor stereotypes for the implementation, and higher psychophysiological processes. The maturation and implementation of the functions of the cerebral cortex are described in detail in specialized materials for students of the pediatric faculty in topic 11, v. 3, topics 1-8.

The hematoliquor and blood-brain barriers in the postnatal period have a number of features.

In the early postnatal period, large veins are formed in the choroid plexuses of the ventricles of the brain, which can deposit a significant amount of blood 14, thereby participating in the regulation of intracranial pressure.

CORTEX (cortexencephali) - all surfaces of the cerebral hemispheres, covered with a cloak (pallium), formed by gray matter. Together with other departments of c. n. With. the bark is involved in the regulation and coordination of all body functions, plays an extremely important role in mental, or higher nervous activity (see).

In accordance with the stages of evolutionary development of c. n. With. the bark is divided into old and new. The old cortex (archicortex - the old cortex itself and paleocortex - the ancient cortex) is a phylogenetically older formation than the new cortex (neocortex), which appeared during the development of the cerebral hemispheres (see Architectonics of the cerebral cortex, Brain).

Morphologically, K. m. is formed by nerve cells (see), their processes and neuroglia (see), which has a support-trophic function. In primates and humans in the cortex, there are approx. 10 billion neurocytes (neurons). Depending on the shape, pyramidal and stellate neurocytes are distinguished, which are characterized by great diversity. The axons of pyramidal neurocytes are sent to the subcortical white matter, and their apical dendrites - to the outer layer of the cortex. Star-shaped neurocytes have only intracortical axons. Dendrites and axons of stellate neurocytes branch abundantly near the cell bodies; some of the axons approach the outer layer of the cortex, where, following horizontally, they form a dense plexus with the tops of the apical dendrites of pyramidal neurocytes. Along the surface of the dendrites there are reniform outgrowths, or spines, which represent the region of axodendritic synapses (see). The cell body membrane is the area of ​​axosomatic synapses. In each area of ​​the cortex there are many input (afferent) and output (efferent) fibers. Efferent fibers go to other areas K. of m, to subcrustal educations or to the motive centers of a spinal cord (see). Afferent fibers enter the cortex from the cells of the subcortical structures.

The ancient cortex in humans and higher mammals consists of a single cell layer, poorly differentiated from the underlying subcortical structures. Actually the old bark consists of 2-3 layers.

The new bark has a more complex structure and takes (in humans) approx. 96% of the entire surface of K. g. m. Therefore, when they talk about K. g. m., they usually mean a new bark, which is divided into the frontal, temporal, occipital and parietal lobes. These lobes are divided into areas and cytoarchitectonic fields (see Architectonics of the cerebral cortex).

The thickness of the cortex in primates and humans varies from 1.5 mm (on the surface of the gyri) to 3-5 mm (in the depth of the furrows). On the sections painted across Nissl, the layered structure of bark is visible, a cut depends on grouping of neurocytes at its different levels (layers). In the bark, it is customary to distinguish 6 layers. The first layer is poor in cell bodies; the second and third - contain small, medium and large pyramidal neurocytes; the fourth layer is the zone of stellate neurocytes; the fifth layer contains giant pyramidal neurocytes (giant pyramidal cells); the sixth layer is characterized by the presence of multiform neurocytes. However, the six-layer organization of the cortex is not absolute, since in reality in many parts of the cortex there is a gradual and uniform transition between layers. The cells of all layers, located on the same perpendicular with respect to the surface of the cortex, are closely connected with each other and with subcortical formations. Such a complex is called a column of cells. Each such column is responsible for the perception of predominantly one type of sensitivity. For example, one of the columns of the cortical representation of the visual analyzer perceives the movement of an object in a horizontal plane, the neighboring one - in a vertical one, etc.

Similar cell complexes of the neocortex have a horizontal orientation. It is assumed that, for example, small cell layers II and IV consist mainly of receptive cells and are “entrances” to the cortex, large cell layer V is an “exit” from the cortex to subcortical structures, and middle cell layer III is associative, connects different areas of the cortex.

Thus, several types of direct and feedback connections between the cellular elements of the cortex and subcortical formations can be distinguished: vertical bundles of fibers that carry information from subcortical structures to the cortex and back; intracortical (horizontal) bundles of associative fibers passing at different levels of the cortex and white matter.

The variability and originality of the structure of neurocytes indicate the extreme complexity of the apparatus of intracortical switching and the methods of connections between neurocytes. This feature of the structure of K. g. m should be considered as morfol, the equivalent of its extreme reactivity and funkts, plasticity, providing it with higher nervous functions.

An increase in the mass of the cortical tissue occurred in a limited space of the skull, so the surface of the cortex, which was smooth in lower mammals, was transformed into convolutions and furrows in higher mammals and humans (Fig. 1). It was with the development of the cortex already in the last century that scientists associated such aspects of brain activity as memory (see), intelligence, consciousness (see), thinking (see), etc.

I. P. Pavlov defined 1870 as the year "from which scientific fruitful work on the study of the cerebral hemispheres begins." This year, Fritsch and Gitzig (G. Fritsch, E. Hitzig, 1870) showed that electrical stimulation of certain areas of the anterior section of the CG of dogs causes a contraction of certain groups of skeletal muscles. Many scientists believed that when stimulated by K. m., the “centers” of voluntary movements and motor memory are activated. However still Ch. Sherrington preferred to avoid funkts, interpretations of this phenomenon and was limited only by the statement that the area of ​​bark, irritation a cut causes reduction of muscle groups, is intimately connected with a spinal cord.

Directions of experimental researches K. of m of the end of the last century were almost always connected with problems a wedge, neurology. On this basis, experiments were started with partial or complete decortication of the brain (see). The first complete decortication in a dog was made by Goltz (F. L. Goltz, 1892). The decorticated dog turned out to be viable, but many of its most important functions were sharply impaired - vision, hearing, orientation in space, coordination of movements, etc. partial extirpations of the cortex suffered from the absence of an objective criterion for their evaluation. The introduction of the conditioned reflex method into the practice of experimenting with extirpations opened up a new era in studies of the structural and functional organization of CG m.

Simultaneously with the discovery of the conditioned reflex, the question arose about its material structure. Since the first attempts to develop a conditioned reflex in decorticated dogs failed, I. P. Pavlov came to the conclusion that C. g. m. is an "organ" of conditioned reflexes. However, further studies showed the possibility of developing conditioned reflexes in decorticated animals. It was found that conditioned reflexes are not disturbed during vertical cuts of various areas of the K. g. m. and their separation from subcortical formations. These facts, along with electrophysiological data, gave reason to consider the conditioned reflex as a result of the formation of a multichannel connection between various cortical and subcortical structures. The shortcomings of the method of extirpation for studying the significance of C. g. m in the organization of behavior prompted the development of methods for reversible, functional, exclusion of the cortex. Buresh and Bureshova (J. Bures, O. Buresova, 1962) applied the phenomenon of the so-called. spreading depression by applying potassium chloride or other irritants to one or another part of the cortex. Since depression does not spread through the furrows, this method can only be used on animals with a smooth surface K. g. m. (rats, mice).

Other way funkts, switching off K. g. m. - its cooling. The method developed by N. Yu. Belenkov et al. (1969), consists in the fact that, in accordance with the shape of the surface of the cortical areas scheduled for shutdown, capsules are made that are implanted over the dura mater; during the experiment, a cooled liquid is passed through the capsule, as a result of which the temperature of the cortex under the capsule decreases to 22–20°C. The assignment of biopotentials with the help of microelectrodes shows that at such a temperature, the impulse activity of neurons stops. The cold decortication method used in hron, experiments on animals demonstrated the effect of an emergency shutdown of the new cortex. It turned out that such a switch-off stops the implementation of previously developed conditioned reflexes. Thus, it was shown that K. g. m. is a necessary structure for the manifestation of a conditioned reflex in an intact brain. Consequently, the observed facts of the development of conditioned reflexes in surgically decorticated animals are the result of compensatory rearrangements occurring in the time interval from the moment of the operation to the beginning of the study of the animal in hron, experiment. The compensatory phenomena take place and in case funkts, switching-offs of a new bark. Just like cold shutdown, acute shutdown of the neocortex in rats with the help of spreading depression sharply disrupts conditioned reflex activity.

A comparative evaluation of the effects of complete and partial decortication in various animal species showed that monkeys endure these operations more difficult than cats and dogs. The degree of dysfunction during extirpation of the same areas of the cortex is different in animals at different stages of evolutionary development. For example, the removal of temporal regions in cats and dogs impairs hearing less than in monkeys. Similarly, vision after removal of the occipital lobe of the cortex is affected to a greater extent in monkeys than in cats and dogs. On the basis of these data there was an idea of ​​corticolization of functions in the course of evolution of c. n. N of page, according to Krom phylogenetically earlier links of a nervous system pass to lower level of hierarchy. At the same time, K. g. m. plastically rebuilds the functioning of these phylogenetically older structures in accordance with the influence of the environment.

Cortical projections of afferent systems K. of m represent specialized end stations of ways from sensory organs. Efferent pathways go from K. m. to the motor neurons of the spinal cord as part of the pyramidal tract. They originate mainly from the motor area of ​​the cortex, which in primates and humans is represented by the anterior central gyrus, located anterior to the central sulcus. Behind the central sulcus is the somatosensory area K. m. - the posterior central gyrus. Individual parts of the skeletal muscles are corticolized to varying degrees. The lower limbs and trunk are represented least differentiated in the anterior central gyrus, the representation of the muscles of the hand occupies a large area. An even larger area corresponds to the musculature of the face, tongue and larynx. In the posterior central gyrus, in the same ratio as in the anterior central gyrus, afferent projections of body parts are presented. It can be said that the organism is, as it were, projected into these convolutions in the form of an abstract "homunculus", which is characterized by an extreme preponderance in favor of the anterior segments of the body (Fig. 2 and 3).

In addition, the cortex includes associative, or non-specific, areas that receive information from receptors that perceive irritations of various modalities, and from all projection zones. The phylogenetic development of C. g. m. is characterized primarily by the growth of associative zones (Fig. 4) and their separation from projection zones. In lower mammals (rodents), almost the entire cortex consists of projection zones alone, which simultaneously perform associative functions. In humans, the projection zones occupy only a small part of the cortex; everything else is reserved for associative zones. It is assumed that associative zones play a particularly important role in the implementation of complex forms in c. n. d.

In primates and humans, the frontal (prefrontal) region reaches the greatest development. It is phylogenetically the youngest structure directly related to the highest mental functions. However, attempts to project these functions to separate areas of the frontal cortex have not been successful. Obviously, any part of the frontal cortex can be included in the implementation of any of the functions. The effects observed during the destruction of various parts of this area are relatively short-lived or often completely absent (see Lobectomy).

The confinement of separate structures of K. of m to certain functions, considered as a problem of localization of functions, remains till now one of the most difficult problems of neurology. Noting that in animals, after the removal of the classical projection zones (auditory, visual), conditioned reflexes to the corresponding stimuli are partially preserved, I. P. Pavlov hypothesized the existence of a "core" of the analyzer and its elements, "scattered" throughout the C. g. With the help microelectrode research methods (see) it was succeeded to register activity of the specific neurocytes responding to incentives of a certain touch modality in various areas K. of m. Superficial assignment of bioelectric potentials reveals distribution of primary evoked potentials on the considerable areas K. of m - outside of the corresponding projection zones and cytoarchitectonic fields. These facts, along with the poly-functionality of disorders during the removal of any sensory area or its reversible shutdown, indicate a multiple representation of functions in the C. g. m. Motor functions are also distributed over large areas of the C. g. m. tract, are located not only in the motor areas, but also beyond them. In addition to sensory and motor cells, in K. m. there are also intermediate cells, or interneurocytes, which make up the bulk of K. g. m. and concentrated ch. arr. in association areas. Multimodal excitations converge on interneurocytes.

Experimental data indicate, thus, the relativity of the localization of functions in C. g. m., the absence of cortical "centers" reserved for one or another function. The least differentiated in funkts, the relation are the associative areas possessing especially expressed properties of plasticity and interchangeability. However, it does not follow from this that the associative regions are equipotential. The principle of equipotentiality of the cortex (the equivalence of its structures), expressed by Lashley (K. S. Lashley) in 1933 on the basis of the results of extirpations of a poorly differentiated rat cortex, as a whole cannot be extended to the organization of cortical activity in higher animals and humans. I. P. Pavlov contrasted the principle of equipotentiality with the concept of dynamic localization of functions in C.G.M.

The solution to the problem of the structural and functional organization of C. g. m. is largely hampered by the identification of the localization of symptoms of extirpations and stimulations of certain cortical zones with the localization of the functions of C. g. m. This question already concerns the methodological aspects of neurophysiol, experiment, since from a dialectical point From the point of view of any structural-functional unit in the form in which it appears in each given study, it is a fragment, one of the aspects of the existence of the whole, a product of the integration of structures and connections of the brain. For example, the position that the function of motor speech is "localized" in the lower frontal gyrus of the left hemisphere is based on the results of damage to this structure. At the same time, electrical stimulation of this "center" of speech never causes an act of articulation. It turns out, however, that the utterance of entire phrases can be induced by stimulation of the rostral thalamus, which sends afferent impulses to the left hemisphere. Phrases caused by such stimulation have nothing to do with arbitrary speech and are not adequate to the situation. This highly integrated stimulation effect indicates that ascending afferent impulses are transformed into a neuronal code effective for the higher coordination mechanism of motor speech. In the same way, complexly coordinated movements caused by stimulation of the motor area of ​​the cortex are organized not by those structures that are directly exposed to irritation, but by neighboring or spinal and extrapyramidal systems excited along descending pathways. These data show that there is a close relationship between the cortex and subcortical formations. Therefore, it is impossible to oppose cortical mechanisms to the work of subcortical structures, but it is necessary to consider specific cases of their interaction.

With electrical stimulation of individual cortical areas, the activity of the cardiovascular system, the respiratory apparatus, went. - kish. a path and other visceral systems. K. M. Bykov also substantiated the influence of CGM on the internal organs by the possibility of the formation of visceral conditioned reflexes, which, along with vegetative shifts with various emotions, was put by him as the basis for the concept of the existence of cortico-visceral relations. The problem of cortico-visceral relations is solved in terms of studying the modulation by the cortex of the activity of subcortical structures that are directly related to the regulation of the internal environment of the body.

An essential role is played by communications K. of m with a hypothalamus (see).

The level of activity of K. m. is mainly determined by ascending influences from the reticular formation (see) of the brain stem, which is controlled by cortico-fugal influences. The effect of the last has dynamic character and is a consequence of the current afferent synthesis (see). Studies using electroencephalography (see), in particular corticography (i.e., the assignment of biopotentials directly from K. g. m.), It would seem that they confirmed the hypothesis about the closure of the temporary connection between the foci of excitations that occur in the cortical projections of the signal and unconditioned stimuli in the process of formation of a conditioned reflex. However, it turned out that as the behavioral manifestations of the conditioned reflex become stronger, the electrographic signs of the conditioned connection disappear. This crisis of the technique of electroencephalography in the knowledge of the mechanism of the conditioned reflex was overcome in the studies of M. N. Livanov et al. (1972). They showed that the spread of excitation along C. g. m. and the manifestation of a conditioned reflex depend on the level of distant synchronization of biopotentials removed from spatially remote points of C. g. m. An increase in the level of spatial synchronization is observed with mental stress (Fig. 5). In this state, synchronization areas are not concentrated in certain areas of the cortex, but are distributed over its entire area. Correlation relations cover points of the entire frontal cortex, but at the same time, increased synchrony is also recorded in the precentral gyrus, in the parietal region, and in other parts of the C. g. m.

The brain consists of two symmetrical parts (hemispheres) interconnected by commissures consisting of nerve fibers. Both hemispheres of the brain are united by the largest commissure - the corpus callosum (see). Its fibers connect identical points of the K. g. m. The corpus callosum ensures the unity of the functioning of both hemispheres. When it is cut, each hemisphere begins to function independently of one another.

In the process of evolution, the human brain acquired the property of lateralization, or asymmetry (see). Each of its hemispheres specialized to perform certain functions. In most people, the left hemisphere is dominant, providing the function of speech and control over the action of the right hand. The right hemisphere is specialized for the perception of form and space. At the same time funkts, differentiation of hemispheres is not absolute. However, extensive damage to the left temporal lobe is usually accompanied by sensory and motor speech disorders. Obviously, lateralization is based on innate mechanisms. However, the potential of the right hemisphere in organizing the function of speech can manifest itself when the left hemisphere is damaged in newborns.

There are reasons to consider lateralization as an adaptive mechanism that developed as a result of the complication of brain functions at the highest stage of its development. Lateralization prevents the interference of various integrative mechanisms in time. It is possible that cortical specialization counteracts the incompatibility of various functional systems (see), facilitates decision-making about the purpose and mode of action. The integrative activity of the brain is not limited, therefore, to the external (summative) integrity, understood as the interaction of the activities of independent elements (be it neurocytes or entire brain formations). Using the example of the development of lateralization, one can see how this integral, integrative activity of the brain itself becomes a prerequisite for the differentiation of the properties of its individual elements, endowing them with functionality and specificity. Consequently, the funkts, the contribution of each individual structure of the C. g. m., in principle, cannot be assessed in isolation from the dynamics of the integrative properties of the whole brain.

Pathology

The cerebral cortex is rarely affected in isolation. Signs of its defeat to a greater or lesser extent usually accompany the pathology of the brain (see) and are part of its symptoms. Usually patol, not only K. of m, but also white matter of hemispheres is surprised by processes. Therefore, pathology K. of m is usually understood as its primary lesion (diffuse or local, without a strict boundary between these concepts). The most extensive and intense lesion of K. m. is accompanied by the disappearance of mental activity, a complex of both diffuse and local symptoms (see Apallic syndrome). Along with nevrol, symptoms of damage to the motor and sensitive spheres, symptoms of damage to various analyzers in children is a delay in the development of speech and even the complete impossibility of the formation of the psyche. In this case, changes in cytoarchitectonics are observed in the form of a violation of layering, up to its complete disappearance, foci of loss of neurocytes with their replacement by growths of glia, heterotopia of neurocytes, pathology of the synaptic apparatus and other pathomorphol changes. Lesions of K. m. hereditary and degenerative diseases of the brain, disorders of cerebral circulation, etc.

Studying of EEG at localization patol, the center in K. of m reveals dominance of focal slow waves which are considered as a correlate of guarding braking more often (U. Walter, 1966). Weak expressiveness of slow waves in the field patol, the center is a useful diagnostic sign in a preoperative assessment of a condition of patients. As N. P. Bekhtereva's researches (1974) carried out jointly with neurosurgeons showed, the absence of slow waves in the area patol, the focus is an unfavorable prognostic sign of the consequences of surgical intervention. For an assessment patol, K.'s state of m also the test for interaction of EEG in a zone of focal defeat with the caused activity is used in response to positive and differentiating conditional irritants. The bioelectric effect of such an interaction can be both an increase in focal slow waves, and a weakening of their severity or an increase in frequent oscillations such as pointed beta waves.

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H. Yu. Belenkov.