Dynamic localization of functions in the cerebral cortex. Three main functional blocks of the brain (Luria A.R.) Associative part of the brain

The figure also shows several large areas of the cerebral cortex, not fitting into rigid categories of primary or secondary motor and sensory areas. These areas are called association areas because they receive and analyze signals simultaneously from many regions of both the motor and sensory cortices, as well as from subcortical structures. However, association areas have their own specific functions.

Most important association areas are: (1) parieto-occipital-temporal region; (2) prefrontal association area; (3) limbic association area. The functions of these areas are explained below.

Parieto-occipital-temporal region. This association area occupies a large area of the parietal and occipital cortex, bounded in front by the somatosensory cortex, behind by the visual cortex, and laterally by the auditory cortex. It provides a high level of analysis of the semantic meaning of signals from all surrounding sensory areas. However, the homogeneous parieto-occipito-temporal association area has its own functional division.

1. Analysis of body spatial coordinates(body coordination in space). An area that begins in the posterior parietal cortex and extends into the superior occipital cortex, provides constant analysis of the spatial coordinates of all parts of the body, as well as everything that surrounds it. This area receives visual sensory information from the posterior occipital cortex and simultaneously somatosensory information from the anterior parietal cortex.
Based on all this information The coordinates of the surrounding space, perceived through vision, hearing and the surface of the body, are calculated.

2. Speech understanding area. A large area for speech comprehension, called Wernicke's area, lies behind the primary auditory cortex in the posterior part of the superior gyrus of the temporal lobe. We will discuss this area in more detail below. This is the most important area of the brain for higher intellectual functions, since speech underlies almost all of these functions.

3. Primary processing area“visual” speech (reading). Behind the language comprehension area, mainly in the anterolateral region of the occipital lobe, is the visual association area, which sends visual information conveyed by words read in a book to Wernicke's area, the area of speech understanding. This so-called angular gyrus region is essential for understanding the meaning of visually perceived words. In its absence, a person can perfectly understand speech by ear, but not when reading.

4. Object naming area. In the most lateral parts of the anterior occipital lobe and the posterior temporal lobe there is an area for naming objects. We mostly recognize the names of objects when we hear them, i.e. with the help of the organ of hearing, while we perceive the physical nature of an object by its appearance, i.e. using vision.

In turn, the names important for understanding speech and listening, and during reading (functions performed by Wernicke's area, located directly above the area of audible “names” and in front of the area that analyzes visible words).

Associative systems of the brain, their role in the sensory function of the brain and programming of behavior.

One of the main attributes of any complex purposeful movement is the formation of preliminary programs.
The role of the program in the structure of a motor act should be considered taking into account the biological motivation of the movement, its temporal parameters, motor differentiation, the degree of complexity of the coordination structure and the level of its automated strategy and tactics of movement. The biological motivation of a motor act is the main motivating (initial) factor for its implementation. It is motivations that form purposeful movements, and therefore determine their overall strategy. This means that if the movement strategy is based on biological (or social) motivation, then each specific motor act will be considered as a step towards satisfying this motivation, that is, it will solve some intermediate task or goal (Fig. 104). Biological motivations can lead either to the launch of “sealed”, that is, rigid, programs, establish their combinatorics, which we encounter in invertebrates and lower vertebrates and call instincts or complexes of fixed actions, or lead to the formation of new complex programs, simultaneously defining the degree of their lability. in cases where the action is completely an automatic consequence of the stimulus, it is impossible to talk about motivation. In this case, there are fixed relationships between the stimulus and the response. Motivation “breaks” these fixed connections between stimulus and response through the process of learning. For example, unlike many instinctive reactions, the reaction of pressing a pedal can be “separated” from the internal state of the animal. The operant situation, signal, reaction, reinforcement are completely arbitrary, not having fixed connections with each other.

Participation of associative systems of the brain in the organization of movement. The role of external factors, signals from the external environment and, accordingly, the role of sensory and associative systems of the brain in the formation of motivated movements is very significant. The specificity of the participation of the thalamoparietal associative system in the organization of movements is determined by two points.

On the one hand, it participates in the formation of an integrated circuit of the body, all parts of which are correlated not only with each other, but also with vestibular and visual signals.

On the other hand, it is involved in regulating attention to current environmental signals, taking into account the orientation of the whole body relative to these signals.

The thalamoparietal (like the inferotemporal) associative system is activated by current sensory signals, that is, it is mainly tied to the present moment in time, and is associated with the analysis of mainly spatial relationships of raziomodal features.

The frontal associative system has a reciprocal relationship with two functional systems of the brain:

1) parietal-temporal, which is associated with the processing and integration of multimodal sensory information;

2) telecephalic limbic system, including the limbic cortex and associated subcortical formations, especially the hypothalamus and areas of the midbrain and diencephalon.

Purposeful behavior is determined by the dominant motivation, which encourages the body to satisfy the prevailing need.

The adaptive nature of behavior is achieved with the help of many conditioned reflexes, which ensure the adaptation of the organism to a specific spatio-temporal situation. The nonspecific direction of search behavior is determined by the presence of a hypothalamic focus of stationary excitation, which has dominant properties (inertia, high excitability, ability to summation); search activity in a specific situation is determined by a system of cortical conditioned reflex connections as the basis of past life experience, which provides a directed search for an object to satisfy a need.

Higher integrative (associative) systems of the brain are the main apparatuses for controlling plastic forms of behavior, which are provided by the following mechanisms:

♦ selective convergence of biologically significant information;

♦ plastic changes under the influence of dominant motivation;

♦ short-term storage of integral images and programs for the upcoming behavioral act.

The degree of development of associative systems of the brain in the evolution of mammals correlates with the perfection of apaltic-sypthetic activity and the organization of complex forms of behavior.

The ability to form a sequence of movements and anticipate its implementation, as the most complex function of the brain, reaches its greatest development in a person who has the properties of verbal control of behavior.

Further increase in the quantity and quality of the child’s motor activity is associated with the completion of the primary formation of the neural substrate as part of the kinesthetic analyzer, the improvement of intracortical, cortical-subcortical pathways, functional connections between the motor and associative areas of the cerebral cortex, as well as subcortical structures. The optimal mode of operation of the musculoskeletal system in humans is established by the age of 20-25 years.

5.2. PHYSIOLOGY OF THE SPINAL CORD

5.2.1. Structural and functional characteristics

A. Segments. The spinal cord is a cord about 45 cm long in men and about 42 cm in women, and has a segmental structure (31-33 segments); each section is associated with a specific part of the body. The spinal cord includes five sections:

cervical (CI-CVIII), thoracic (ThI-ThXII), lumbar (LI-LV), sacral (SI-SV) and coccygeal (COI-COIII).

In the process of evolution, two thickenings were formed - cervical (segments innervating the upper limbs) and lumbosacral (segments innervating the lower limbs) as a result of increased load on these parts of the spinal cord. Some species of animals do not have such thickenings, for example, a snake, which moves thanks to the uniform participation of all the muscles of the body in the process of movement. Training any organ ensures its progressive development not only in phylo-, but also in ontogenesis, while, naturally, the function also improves. An organ that does not receive enough load gradually atrophies. Somatic neurons in these thickenings of the spinal cord are the largest, there are more of them, each root of these segments contains more nerve fibers than in other roots, they are the thickest.

B. Neurons of the spinal cord. The total number of neurons is about 13 million (3% motor neurons, 97% interneurons, also related to the autonomic nervous system). Their It is advisable to classify according to several criteria:

In the nervous system department - neurons of the somatic and autonomic nervous system;

By purpose, i.e. according to the direction of information - efferent, afferent, intercalary;

By influence - exciting and inhibitory.

Efferent neurons spinal cord, related to the somatic nervous system, are effector, since they directly innervate the working organs - effectors (skeletal muscles), they are called motor neurons. There are α- and γ-motoneurons. α-Motoneurons innervate extrafusal muscle fibers (skeletal muscles), their axons are characterized by a high speed of excitation -70-1 20 m/s. α -Motoneurons are divided into two subgroups: α 1 - fast, innervating white muscle fibers, their lability is about 30 impulses / s, and 02 - slow, innervating red muscle fibers, their lability is 10-15 impulses / s. Low lability α -motoneurons is explained by the long-term trace hyperpolarization that accompanies the AP. On one α -motoneurons have up to 20,000 synapses: from skin receptors, proprioceptors and descending pathways of the overlying parts of the central nervous system. γ-Motoneurons scattered among α -motoneurons, their activity is regulated by neurons of the overlying sections CNS, they innervate the intrafusal muscle fibers of the muscle spindle (muscle receptor). When the contractile activity of intrafusal fibers changes under the influence γ- Motor neurons change the activity of muscle receptors. Impulse from muscle receptors activates α -motoneurons of the same muscle and inhibits α -motoneurons of the antagonist muscle, thereby regulating the tone of skeletal muscles and motor reactions. These neurons have high lability - up to 200 impulses / s, but their axons are characterized by a lower excitation speed - 10-40 m / s.

Afferent neurons of the somatic nervous system are localized in the spinal ganglia and ganglia of the cranial nerves. Their processes, conducting afferent impulses from muscle, tendon and skin receptors, enter the corresponding segments of the spinal cord and form synaptic contacts either directly on α -motoneurons (excitatory synapses), or on interneurons, which can be excitatory and inhibitory.

Intercalary neurons establish communication with motor neurons of the spinal cord and sensory neurons.

They also provide connection between the spinal cord and the nuclei of the brain stem, and through them, with the cerebral cortex. They can be both exciting and inhibitory; they are characterized by high lability - up to 1000 impulses/s.

Association neurons form their own spinal cord apparatus, establishing connections between segments and within segments. The associative apparatus of the spinal cord is involved in the coordination of posture, muscle tone, movements of the limbs and torso.

Reticular formation of the spinal cord consists of thin crossbars of gray matter intersecting in different directions, its neurons have numerous processes. The reticular formation is found at the level of the cervical segments between the anterior and posterior horns, and at the level of the upper thoracic segments - between the lateral and posterior horns in the white matter adjacent to the gray.

Neurons of the autonomic nervous system are also intercalary; sympathetic nervous system neurons located in the lateral horns of the thoracic, lumbar and partially cervical parts of the spinal cord (CVIII-LII) and are background active, their discharge frequency is 3-5 pulses/s. Parasympathetic neurons of the autonomic nervous system are localized in the sacral spinal cord (82-84) and are also background active.

B. A collection of neurons forms various nerve centers. The spinal cord contains the regulatory centers for most internal organs and skeletal muscles. Various sympathetic centers of the autonomic nervous system are localized in such segments as the center of the pupillary reflex - CVIII-TII, regulation of heart activity - ThI-ThV, salivation - ThII-ThIV, regulation of kidney function - ThV-LIII. The centers that regulate the functions of sweat glands and blood vessels, smooth muscles of internal organs, and centers of pilomotor reflexes are located segmentally. Parasympathetic innervation All pelvic organs are obtained from the spinal cord (SII-SIV): the bladder, part of the colon below its left bend, and the genitals. In men, parasympathetic innervation provides the reflex component of erection, in women - vascular reactions of the clitoris and vagina.

Skeletal muscle control centers are located in all parts of the spinal cord and innervate, according to a segmental principle, the skeletal muscles of the neck (CI-CIV), diaphragm (CIII-CV), upper extremities (CV-ThII), trunk (ThIII-LI) and lower extremities (LII-SV).

Moscow Institute of Humanities and Economics

Tver branch

Department of Applied Psychology

Abstract on the discipline

"Physiology of higher nervous activity and sensory systems"

Topic: “Functional organization of the brain.”

Introduction

Conclusion

Bibliography

Introduction

Opening of I.P. Pavlov's analyzers and the creation of the doctrine of conditioned reflexes, which was based on an objective analysis of the dynamics of nervous processes, served as the basis for the development of modern materialistic ideas about the dynamic localization of brain functions - the holistic and at the same time differentiated involvement of the brain in any of the forms of its activity.

Proposed by I.P. Pavlov’s objective conditioned reflex research method made it possible to most adequately approach the experimental solution to the problem of the functional organization of the brain. I.P. Pavlov developed and experimentally substantiated the idea of analyzer systems, where each analyzer is a specific anatomically localized structure from peripheral receptor formations to the projection zones of the cerebral cortex. He suggested that in addition to the local projection zones of the cortex, acting as the “core of the cortical end of the analyzer” (or projection zones of the cortex), there are peripheral zones of representation of each analyzer, the so-called “zones of scattered elements.” Due to this structural organization, all analyzers, including the motor analyzer, overlap with their peripheral (cortical) zones and form secondary projection zones of the cortex, which I.P. Pavlov even then considered the “associative centers” of the brain to be the basis for the dynamic interaction of all analytical systems.

From the standpoint of systemic organization of functions in brain activity, various functional systems and subsystems are distinguished. The classic version of integrative brain activity can be presented in the form of the interaction of three main functional blocks:

1) block for receiving and processing sensory information - sensory systems (analyzers);

2) block of modulation, activation of the nervous system - modulating systems (limbic-reticular systems) of the brain;

3) block of programming, launching and control of behavioral acts - motor systems (motor analyzer).

1. Three main functional blocks of the brain

1.1 Block for receiving and processing sensory information

The first functional block consists of analyzers, or sensor systems. Analyzers perform the function of receiving and processing signals from the external and internal environment of the body. Each analyzer is tuned to a specific signal modality and provides a description of the entire set of signs of perceived stimuli.

The analyzer is a multi-level system with a hierarchical design principle. The base of the analyzer is the receptor surface, and the top is the projection zones of the cortex. Each level of this morphologically ordered structure is a collection of cells, the axons of which go to the next level (the exception is the upper level, the axons of which extend beyond the limits of this analyzer). The relationship between successive levels of analyzers is built on the principle of “divergence - convergence”. The higher the neural level of the analyzer system, the greater the number of neurons it includes. At all levels of the analyzer, the principle of topical projection of receptors is preserved. The principle of multiple receptotopic projection facilitates multiple and parallel processing (analysis and synthesis) of receptor potentials (“excitation patterns”) that arise under the influence of stimuli.

A neuron located at the output of the receptive field can highlight one sign of a stimulus (simple detectors) or a complex of its properties (complex detectors). The detector properties of a neuron are determined by the structural organization of its receptive field. Neurons-detectors of a higher order are formed as a result of the convergence of neurons-detectors of a lower (more elementary) level. Neurons that detect complex properties form detectors of “super complex” complexes. The highest level of hierarchical organization of detectors is achieved in the projection zones and association areas of the cerebral cortex.

The projection zones of the analyzing systems occupy the outer (convexital) surface of the neocortex of the posterior parts of the brain. This includes the visual (occipital), auditory (temporal) and sensory (parietal) areas of the cortex. The cortical section of this functional block also includes the representation of taste, olfactory, and visceral sensitivity.

The primary projection zones of the cortex consist mainly of neurons of the 4th afferent layer, which are characterized by a clear topical organization. A significant portion of these neurons have the highest specificity. Neurons of the visual apparatus of the cortex react only to highly specialized properties of visual stimuli (shades of color, character of lines, direction of movement). However, it should be noted that the primary zones of individual cortical areas also include multimodal neurons that respond to several types of stimuli.

Secondary projection zones of the cortex are located around the primary zones, as if built on top of them. In these zones, the 4th afferent layer gives way to the leading place of the 2nd and 3rd cell layers. These neurons are characterized by the detection of complex features of stimuli, but at the same time they retain the modal specificity corresponding to the neurons of the primary zones. Therefore, it is assumed that the complication of the detector selective properties of neurons in the secondary zones can occur through the convergence of neurons in the primary zones on them. The primary visual cortex (17th Brodmann area) contains mainly neurons-detectors of simple signs of object vision (detectors of the orientation of lines, stripes, contrast, etc.), and in the secondary zones (18th and 19th Brodmann areas ) detectors of more complex contour elements appear: edges, limited length lines, corners with different orientations, etc. The primary (projection) zones of the auditory (temporal) cortex are represented by the 41st Brodmann area (Fig. 1), the neurons of which are modally specific and respond to various properties of sound stimuli. Like the primary visual field, these primary sections of the auditory cortex have a clear receptotopy. Above the apparatus of the primary auditory cortex are built secondary zones of the auditory cortex, located in the outer parts of the temporal region (22nd and partially 21st Brodmann areas). They also consist predominantly of a powerfully developed 2nd and 3rd layer of cells that react selectively simultaneously to several frequencies and intensities: the sound stimulus.

Rice. 1. Map of cytoarchitectonic fields of the cerebral cortex. Convexital surface of the cerebral cortex: a - primary fields; b - secondary fields; c - tertiary fields

Finally, the same principle of functional organization is preserved in the general sensory (parietal) cortex. The basis here too is the primary or projection zones (3rd, 1st and 2nd Brodmann fields), the thickness of which also predominantly consists of modally specific neurons of the 4th layer, and the topography is distinguished by a clear somatotopic projection of individual body segments. As a result, irritation of the upper parts of this zone causes the appearance of skin sensations in the lower extremities, middle areas - in the upper extremities of the contralateral side, and irritation of the points of the lower zone of this zone - corresponding sensations in the contralateral parts of the face, lips and tongue. Above the primary zones are the secondary zones of the general sensitive (parietal) cortex (5th and partially 40th Brodmann area), consisting mainly of neurons of the 2nd and 3rd layers, and their irritation leads to the emergence of more complex forms of cutaneous and kinesthetic sensitivity (see Fig. 1).

Thus, the main, modality-specific zones of the brain analyzers are built according to a single principle of hierarchical structural and functional organization. Primary and secondary zones, according to I.P. Pavlov, constitute the central part, or core, of the analyzer in the cortex, the neurons of which are characterized by selective tuning to a specific set of stimulus parameters and provide mechanisms for fine analysis and differentiation of stimuli. The interaction of primary and secondary zones is complex, ambiguous in nature and, under conditions of normal activity, determines a coordinated community of processes of excitation and inhibition, which consolidates the macro- and microstructure of the nervous network engaged in the analysis of afferent flow in the primary projection sensory fields. This creates the basis for dynamic inter-analyzer interaction carried out in the associative zones of the cortex.

Associative areas (tertiary zones) of the cortex are a new level of integration: they occupy the 2nd and 3rd cellular (associative) layers of the cortex, where powerful afferent flows meet, both unimodal, multimodal, and nonspecific. The vast majority of associative neurons respond to generalized features of stimuli - the number of elements, spatial position, relationships between elements, etc.

Convergence of multimodal information is necessary for holistic perception, for the formation of a “sensory model of the world”, which arises as a result of sensory learning.

Association zones are located on the border of the occipital, temporal and posterior parietal cortices. The work of these parts of the cerebral cortex is necessary not only for the successful synthesis and differentiation of selective discrimination of stimuli perceived by a person, but also for the transition to the level of their symbolization - for operating with the meanings of words and using them for abstract thinking.

Clinical observations of various focal lesions of the tertiary zones of the human brain have accumulated a large amount of material on the relationship of associative areas with various functional disorders. It is known that lesions of the frontal-temporo-parietal region, the so-called speech zones (meaning the left hemisphere), are associated with the occurrence of aphasia (speech disorder). When the inferotemporal region is damaged, object agnosia is observed (impaired recognition process), parietal areas or the angular gyrus of the parietal lobe - the development of optical-spatial agnosia, when the left temporal lobe is damaged, color agnosia is detected, etc. It should be noted that local lesions of the associative zones of the cortex can be associated with both relatively elementary sensory disorders and disorders of complex forms of perception.

1.2 Block of modulation, activation of the nervous system

The block of modulating brain systems regulates the tone of the cortex and subcortical formations, optimizes the level of wakefulness in relation to the activity being performed and determines an adequate choice of behavior in accordance with the actualized need. Only under conditions of optimal wakefulness can a person best receive and process information, recall the necessary selective systems of connections in memory, program activities, and exercise control over them.

Under conditions of optimal excitability of the cortex, nervous processes are characterized by a certain concentration, balance of excitation and inhibition, the ability to differentiate and, finally, high mobility of nervous processes that determine the course of each organized purposeful activity.

The device that acts as a regulator of the level of wakefulness, as well as carrying out selective modulation and updating of the priority of a particular function, is the modulating system of the brain. It is often called the limbic-reticular complex or ascending activating system. The nervous formations of this apparatus include the limbic and nonspecific brain systems with their activating and inactivating structures. Among the activating formations, the reticular formation of the midbrain, the posterior hypothalamus, and the blue spot in the lower parts of the brain stem are primarily distinguished. Inactivating structures include the preoptic area of the hypothalamus, the raphe nuclei in the brain stem, and the frontal cortex.

The most important part of the modulating block of the brain is the activating reticular formation. Phylogenetically, the reticular formation of the brain represents the most ancient morphological formation. In the reticular formation, more or less compact and limited cell accumulations are distinguished - nuclei, distinguished by various morphological features. In this regard, some authors consider the reticular formation as a diffuse, elongated single formation, while others consider it a complex consisting of many differentiated nuclei with different structures and functions. Laterally (from the sides), the reticular formation is surrounded by sensory pathways. Thus, the fibers of the reticular formation are surrounded by a layer of sensory pathways, which form many collaterals to it.

The functional purpose of the reticular formation remained unknown for a long time. Electrophysiological studies have revealed the exclusive role of the reticular formation in the integrative activity of the brain. This discovery was made in 1949 by G. Magun and G. Moruzzi. By stimulation through electrodes implanted into the brainstem (at the level of the midbrain), they were able to obtain a reaction to awaken a sleeping animal. G. Magun called this brain stem system the ascending activating system of the brain.

The fibers of the reticular formation, moving upward, form modulating “inputs” (usually axodendritic synapses) in the higher-lying brain structures, including the old and new cortex. From the old and new cortex originate descending fibers that go in the opposite direction to the structures of the hypothalamus, midbrain and to lower levels of the brain stem. Through descending systems of connections, all underlying formations are under the control and control of those programs that arise in the cerebral cortex and the implementation of which requires modulation of activity and modification of states of wakefulness. Thus, the activation unit with its ascending and descending influences works (according to the feedback principle) as a single self-regulating apparatus, which ensures a change in the tone of the cortex, and at the same time is itself under its control. This apparatus is used to plastically adapt the body to environmental conditions. It contains at its core at least two sources of activation: internal and external. The first is associated with metabolic processes that ensure the internal balance of the body, the second - with the influence of the external environment. The first source of activation is the internal activity of the organism itself, or needs. Any deviations from vital “constants” as a result of changes in nervous or humoral influences or as a result of selective excitation of various parts of the brain lead to the selective “switching on” of certain organs and processes, the combined work of which ensures the achievement of an optimal state for a given type of activity of the body.

The simplest forms of internal activity are associated with respiratory and digestive processes, internal secretion processes and others included in the homeostatic mechanism of self-regulation, which eliminates disturbances in the internal environment of the body due to its reserves. More complex forms of this type of activation are organized into a structure of innate behavior aimed at satisfying a specific need. Naturally, in order to provide a mechanism for instinctive regulation of behavior, very selective and specific activation is necessary. This specific activation may be a function of the brain's limbic system, in which the hypothalamus plays an important role.

The hypothalamus is part of the diencephalon and contains dozens of highly differentiated nuclei with an extensive and versatile system of connections. The hypothalamus coordinates the internal needs of the body with its external behavior aimed at achieving an adaptive effect. The hypothalamus is part of the need-motivational system, being its main executive structure. Moreover, it not only participates in the regulation of individual vital functions (hunger, thirst, sexual desire, active and passive defense), but combines them into complex complexes or systems. Depending on the nature of the nervous and humoral signaling collected in the hypothalamus, it either accumulates or inhibits motivational excitation that determines external behavior.

The second source of activation is associated with exposure to environmental stimuli. Limiting contact with the external environment leads to a significant decrease in the tone (excitability) of the cerebral cortex. Under conditions of severe limitation of sensory information, a person may experience hallucinations, which to some extent compensate for the deficiency of sensory stimulation.

Part of the continuous flow of sensory signals supplied to the cortex by specific (analyzer) systems enters the reticular formation via collaterals. After multiple switchings in its synapses, afferent excitation reaches the higher parts of the brain. These so-called nonspecific activating influences serve as a necessary condition for maintaining wakefulness and carrying out any behavioral reactions. In addition, nonspecific activation is an important condition for the formation of selective properties of cortical neurons in the process of ontogenetic maturation and learning.

In the apparatus of the ascending reticular formation, a mechanism has been formed for converting sensory information into two forms of activation: tonic (generalized) and phasic (local). The tonic form of activation is associated with the function of the lower stem sections of the reticular formation. It generally, diffusely maintains a certain level of excitability in the cortex and subcortical formations. The phasic form of activation is associated with the upper parts of the brain stem, and primarily with the nonspecific thalamic system, which locally and selectively distributes the effects of ascending activation on the subcortical formations, old and new cortex.

Tonic activation is facilitated by an influx of stimulation from various sense organs. The “emergency” appearance or disappearance of any stimulus in the external environment causes an orientation reflex and an activation reaction (emergency mobilization of the body). This is a multicomponent reaction, it is associated with the work of the mechanisms of tonic and phasic activation of the reticular formation (midbrain and nonspecific nuclei of the thalamus). In addition, the orientation reflex is associated with the activating and inhibitory function of neurons in the hippocampus and caudate nucleus, which are an important apparatus for regulating tonic states of the cerebral cortex.

The cerebral cortex, along with its specific functional contribution, has activating and inhibitory influences on underlying nerve formations. Cortical influences coming through descending fibers represent a fairly differentiated organization and can be considered as an additional third source of activation. The descending fibers of the activating (and inhibitory) reticular system have a fairly differentiated cortical organization; If bundles of fibers associated with specific pathways (increasing or decreasing the tone of the sensory or motor apparatus) come from the primary (and partly from the secondary) zones of the cortex, then the fibers that mediate more general activating influences on the reticular formation of the trunk come primarily from the frontal cortex. Descending fibers, coming primarily from the prefrontal (orbital and medial) cortex, are addressed to the nuclei of the thalamus opticus and underlying brainstem formations and are the apparatus through which the higher parts of the cerebral cortex, directly involved in the formation of intentions and plans, control the work of the underlying apparatuses of the reticular formation of the thalamus and trunk, thereby modulating their work and providing the most complex forms of conscious activity.

1.3 Block of programming, launching and monitoring of behavioral acts

Reception, processing and storage of external information constitute only one side of a person’s mental life. Its other side is the organization of active conscious mental activity. The third of the main functional blocks of the brain is associated with this task - the block of programming, regulation and control of ongoing activity.

The apparatuses of the third functional block of the brain are located in the anterior sections of the cerebral hemispheres, in front of the central gyrus (see Fig. 1). Its main distinguishing feature is that it does not contain modality-specific zones representing individual analyzers, but consists entirely of efferent (motor) type apparatuses, however, it itself is under a constant influx of information from the apparatuses of the afferent (sensory) block. The next most important feature that distinguishes the work of the third functional block from the afferent one is that the processes here proceed in a descending direction, starting from the highest - the tertiary and secondary zones of the cortex. Here, in the higher parts of the integrative-starting block, motor programs are formed, and then they move on to the apparatus of lower motor formations (primary cortical zones; stem and spinal motor nuclei). Of decisive importance in the preparation of motor efferent impulses are the secondary (premotor sections, 6th and 8th fields) and tertiary zones (prefrontal sections of the frontal cortex), or frontal lobes built above the primary motor cortex (see Fig. 1).

The motor cortex (primary projection zone) occupies the space rostral to the Rolandic fissure (Brodmann's 4th area). It is the exit gate of the integrative trigger system of the brain, or the functional block of programming, regulation and control of activity. The anterior central gyrus is only the primary (projection) zone, the executive apparatus (exit gate) of the cerebral cortex. Naturally, the composition of motor impulses sent to the periphery must be prepared, included in certain programs, and only after such preparation can the motor impulse program provide the necessary expedient movements. This program is formed both in the apparatus of the anterior central gyrus and in the apparatus built above it.

A feature of the cytoarchitectonic organization of the motor cortex is the powerful development of the 5th efferent layer, which contains giant pyramidal cells of Betz. Pyramidal neurons are located unevenly, in groups with vertical connections between neurons of layers II and IV. The axons of the giant pyramids give rise to long descending fibers that make up a significant part of the “main” motor pathway of the brain - the pyramidal tract, ending on the motor nuclei of the brain and spinal cord, i.e., they form the corticospinal tract. The pyramidal system is closely related to the extrapyramidal system. The latter includes all brain structures related to the control of movements and sending supraspinal projections outside the corticospinal tracts.

The functional organization of the motor cortex has a projection and topographical nature with clearly expressed signs of somatotopic projection: in the medial parts of the surface of the cortex, fibers that control the muscles of the lower extremities originate, nerve cells in the middle parts of the surface of the cortex send axons to the spinal mechanisms of the upper extremities, from the lateral parts descending efferent fibers are directed to the motor nuclei of the cranial nerves of the brain stem and control the muscles of the larynx, mouth, eyes and face. Along the way, all descending fibers intersect and control the muscles of the opposite side of the body. Organs that need the most fine regulation and perform discrete movements have the maximum topical representation in the motor zone of the cortex.

Unlike humans, in animals, in the areas of the precentral gyrus of the cortex, there is a significant overlap of motor and sensory areas, as a result of which this area is called the sensorimotor cortex. A significant part of the afferent inputs of giant pyramidal cells are fibers of the visual, auditory and other analyzers. In this regard, the primary zones of the animal cortex are the area of sensorimotor integration. The modular structure of the sensorimotor cortex is a fundamental prerequisite for synchronous multisensory integration and the formation of efferent impulse discharge. It is assumed that within the anterior central gyrus, the apparatus involved in interneuronal integration is the upper layers of the cortex, consisting of pyramidal dendrites and glial cells. It is known that the ratio of the mass of this extracellular gray matter to the mass of the cells of the anterior central gyrus increases sharply with evolution, so that its value in humans is twice as large as in higher apes, and almost 5 times greater than in lower apes.

Removal of the precentral motor field leads to different consequences in animals with different degrees of hemispheric development. Typically, movement disorders are observed in the form of paresis, muscle spasticity and limitation of the motor repertoire. Removal of field 4 leads to uncompensated disturbances in the movements of the thumb and other fingers, disruption of voluntary movements of the limbs, and physical inactivity. Removal of the hand causes persistent spastic flexion of the fingers and paralysis of the hand, lasting up to one month. There is general weakness and the most striking symptom is the disappearance of expressive and exploratory reactions so characteristic of monkeys. Complete excision of area 4 in a person makes complex and fine movements on the contralateral side of the body impossible, and separate movements of the fingers are not restored.

Using the method of local electrical stimulation, the exact representation of the muscles of the body and limbs in the cortex of humans and animals was established. Local stimulation of the cortex causes reflexion of individual muscles on the opposite side of the body. Discrete movements with the lowest threshold are caused by stimulation of the motor cortex (4th field). These movements are caused by the activation of giant pyramidal cells, which are absent in the postcentral cortex. All this suggests that the motor zone is only a projection zone, the executive apparatus of the cerebral cortex and it cannot function “independently”. The secondary and tertiary zones of the cortex built above them are of decisive importance in the preparation of motor programs for their transmission to giant pyramidal cells.

The secondary zones of the motor cortex or premotor sections of the frontal region morphologically retain the same principle of “vertical organization” that is characteristic of any motor cortex, but are distinguished by the incomparably greater development of the upper cellular layers of the cortex - small pyramids. The premotor cortex obeys the principle of decreasing specificity; it lacks a local somatotopic projection, and the axons of pyramidal cells in this area form efferents that switch to extensive subcortical motor formations. Irritation of the 5th, 7th and 8th fields of the premotor cortex (see Fig. 1) causes not somatotopically limited (local) twitches of individual muscles, but whole complexes of movements that are systemically organized in nature (ballistic eye movements to a certain point in space, slow tracking eye movements, rotation of the head, torso, directed movements of the limbs). This indicates that “command” neurons of the premotor cortex “organize” individual muscle contractions into a holistic motor act.

The premotor areas of the cortex represent a powerful apparatus for multisensory convergence. These associative zones are equipped with a rich and branched system of efferent pathways both to the cortical formations of the rostral pole of the cerebral hemispheres, and to the subcortical formations - specific, nonspecific, associative nuclei of the thalamus, hypothalamus, amygdala, nuclei of the extrapyramidal system; in addition, they form connections with the spinal cord through pyramidal tract.

The most important part of the third functional block of the brain is the tertiary cortical zones, which occupy the prefrontal or frontal regions (see Fig. 1). The frontal regions, according to A.R. Luria, represent a block of programming intentions, evaluating completed actions and correcting mistakes, i.e. apparatus of the most complex forms of regulation of holistic behavior.

A feature of the prefrontal region (associative fields) of the brain is its rich system of connections both with the underlying subcortical formations of the brain and the corresponding sections of the reticular formation, and with all other sections of the cortex. These connections are bilateral, and often monosynaptic in nature, and make the prefrontal cortex structures in the most advantageous position both for receiving and synthesizing the most complex system of afferentations coming from all parts of the brain, and for organizing efferent impulses that make it possible to exert regulatory influences on all of these structures.

The frontal lobes of the cortex consist entirely of small, granular cells, which have mainly short axons and branched dendrites and thus carry associative functions. Receiving activating influences from the reticular formation through ascending bundles of connections, they themselves exert a regulatory influence on it. They give the activity of the nonspecific activating system a differentiated character, bringing the state of activity into accordance with various forms of behavior. As a later ontogenetic “superstructure,” the frontal lobes perform a much more universal function of the general organization of behavior and higher forms of associative activity. They become finally prepared for activity in a child only 4-7 years of age, when associative pathways provide increasing improvement in the mechanisms of combinational (conditioned reflex) activity of the brain in ontogenesis, when the upper longitudinal bundle of nerve fibers establishes a connection between the new fields of the frontal, parietal, occipital and temporal areas of the cortex. The maturation of the associative systems of the brain is reflected in the gradual normalization of various physiological indicators of the body, the dynamic properties of nervous processes, as well as readiness for increased functional load of associative systems.

As I.P. also pointed out. Pavlov, the frontal lobes of the animal brain, in addition to motor-kinesthetic functions, perform complex processes of analysis and synthesis, ensuring the integration of higher functions and the formation of complex temporary connections. In a lobectomized dog, there are no disturbances in the perception of various exteroceptive signals and in the implementation of simple conditioned reflexes, but the ability to consistently perform the motor skills developed before the operation disappears, and purposeful activity is disrupted. Behavior becomes fragmented, inert stereotypical movements appear, memory and spatial orientation are impaired, and hyperactivity appears.

Further research made it possible to clarify the analysis of the functions of the frontal lobes of the brain. The most noticeable changes in behavior occur after lobectomy in anthropoids. A monkey lacking frontal lobes successfully performs simple acts of behavior, but is unable to differentiate between signals used in different situations (for example, when sequentially changing stimuli), and thus cannot carry out a behavioral program that requires storing a trace of the stimulus in memory. In other words, the performance of various types of deferred tasks is disrupted. However, according to K. Pribram, the destruction of the frontal lobes in chimpanzees leads not so much to memory impairment as to behavioral disturbances as a result of the loss of the ability to solve problems due to the emergence of a stable orienting reflex (an undying reaction to all kinds of side stimuli). At the same time, the animal is not capable of a state of “active anticipation” and, under conditions of a long pause, makes a lot of movements, not relating them to the moment of the expected stimulus. Thus, there is reason to believe that the frontal lobes are one of the most important apparatuses that allow the animal to orient itself not only to the present moment, but also to the future.

Neuropsychological data (obtained in a clinical setting) made it possible to identify a number of symptoms associated with local lesions of areas of the frontal cortex, and thus clarify the specifics of their participation. Damage to the premotor area of the frontal part of the brain leads to impaired control over the motor sphere of human activity. Particularly severe consequences occur when the left hemisphere, associated with speech function, is damaged; therefore, the performance of actions caused by verbal instructions suffers, and the level of intellectual activity changes. With damage involving the basal (orbital) parts of any area, which are closely related to the limbic formations of the brain, symptoms are observed that are directly related to the higher control of the internal motivational sphere of the body.

Neuropsychologists and neurophysiologists unanimously believe that one of the most significant aspects of frontal syndrome is a disorder in the ability to plan adequate behavior and take into account the effect of performed actions. The processes of programming, regulation and control of conscious activity largely depend on the prefrontal regions. K. Pribram believes that the frontal lobes form a set of neural programs that give individual experience a known structure and build a “grammar” of behavior. According to A.R. Luria, it is the frontal lobes that carry out the emergency activation of processes that determine complex forms of conscious activity (directly related to speech).

2. Interaction of the three main functional blocks of the brain

We examined modern ideas about the three main functional blocks of the brain and tried to show the role of each of them in the organization of complex mental activity.

It would be wrong to think that each of these blocks can independently carry out one or another form of activity, considering, for example, that the second functional block fully carries out the function of perception and thinking, and the third - the function of movement and construction of actions.

Each form of conscious activity is always a complex functional system and is carried out based on the joint work of all three blocks of the brain, each of which contributes to the implementation of the mental process as a whole.

The facts, which are well established by modern psychology, make this position indisputable.

The time has long passed when psychologists viewed mental functions as isolated “abilities,” each of which could be localized in a specific area of the brain. Another concept was also rejected, according to which mental processes were represented according to the model of a reflex arc, the first part of which was purely afferent in nature and performed the functions of sensation and perception, while the second - effector - part entirely carried out movements and actions.

Modern ideas about the structure of mental processes are based on the model of a reflex ring or a complex self-regulating system, each link of which includes both afferent and efferent components and which, in general, has the character of complex and active mental activity.

Let's look at two examples: perception and movement, or action. We will do this only in very general terms, since a detailed analysis of the structure and brain organization of these processes will be presented in the last part of this book.

It is known that sensation includes motor components, and modern psychology considers sensation, and especially perception, as a reflex act containing both afferent and efferent links (A.N. Leontiev, 1959); To be convinced of the complex active nature of sensations, it is enough to recall that even in animals they include the process of selection of biologically significant characteristics, and in humans - the active coding influence of language (Bruner, 1957; A.A. Lyublinskaya, 1969).

The active nature of processes appears even more clearly in complex objective perception. It is well known that object perception is not only multireceptor in nature, relying on the joint work of a whole group of analyzers, but always includes active motor components. The decisive role of eye movements in visual perception was noted by I.M. Sechenov (1874-1878), but this was proven only recently. In a number of psychophysiological studies, it has been shown that a stationary eye practically cannot perceive an image consisting of many components, and that complex object perception involves active, searching eye movements that highlight the necessary features (A.L. Yarbus, 1965, 1967), and only gradually, as it develops, it takes on a collapsed character (A.V. Zaporozhets, 1967; V.P. Zinchenko et al., 1962).

All these facts convince us that perception is carried out with the joint participation of all those functional blocks of the brain, of which the first provides the necessary tone of the cortex, the second carries out the analysis and synthesis of incoming information, and the third provides directed search movements, thereby creating the active nature of perceptual activity .

The same can be said about the construction of voluntary movement and action.

The participation of efferent mechanisms in the construction of movement is self-evident; however, still N.A. Bernstein (1947) showed that movement cannot be controlled by efferent impulses alone and that its organized flow requires constant afferent processes that signal the state of the joints and muscles, the position of the segments of the moving apparatus and the spatial coordinates in which the movement occurs.

Thus, voluntary movement, and especially objective action, is based on the joint work of the most diverse parts of the brain, and if the devices of the first block provide the necessary muscle tone, without which no coordinated movement would be possible, then the devices of the second block make it possible to carry out those afferent syntheses, in the system of which movement occurs, and the devices of the third block ensure the subordination of movement and action to the corresponding intentions, create programs for performing motor acts and provide that regulation and control of the flow of movements, thanks to which its organized, meaningful nature is preserved.

Conclusion

In this work, three main functional blocks of the cerebral cortex were considered. The first functional block of the cerebral cortex is the block for receiving, processing and storing sensory information. It is located in the posterior sections of the hemispheres and includes the visual (occipital), auditory (temporal) and general sensory (parietal) sections of the cerebral cortex and the corresponding subcortical structures.

The devices of this (as well as the next) block have a hierarchical structure, breaking up into primary (projection) zones, which receive information and split it into the smallest components, secondary (projection-associative) zones, which provide coding (synthesis) of these components and transform somatotopic projection into the functional organization, and tertiary zones (or overlapping zones), ensuring the joint work of various analyzers and the development of supramodal (symbolic) schemes that underlie complex forms of cognitive activity.

The indicated hierarchically constructed zones of the cortex of the disassembled block work according to the principles of decreasing modal specificity and increasing functional lateralization. Both of these principles provide the possibility of the most complex forms of brain work that underlie the highest types of human cognitive activity, genetically associated with labor, and structurally with the participation of speech in the organization of mental processes.

The second functional unit of the brain plays an important role in regulating cortical activity states and wakefulness levels. This block is built according to the type of nonspecific nervous network, which carries out its function through a gradual, gradual change in states and is not directly related to the reception and processing of information coming from outside, or to the development of intentions, plans and behavior programs. In this way, the second functional block of the brain, located mainly within the brain stem, formations of the interstitial brain and the medial sections of the neocortex, differs significantly from the apparatus of the first functional block of the brain, the main function of which is to receive, process and store external information.

The third functional block of the brain is the block of programming, regulation and control of ongoing activities.

The apparatuses of the third functional block of the brain are located in the anterior sections of the cerebral hemispheres, in front of the central gyrus. It consists entirely of devices of the efferent (motor) type, but is itself under a constant influx of information from the devices of the afferent (sensory) block. The next most important feature that distinguishes the work of the third functional block from the afferent one is that the processes here proceed in a descending direction, starting from the highest - the tertiary and secondary zones of the cortex. Here, in the higher parts of the integrative-starting block, motor programs are formed, and then they move on to the apparatus of lower motor formations (primary cortical zones; stem and spinal motor nuclei).

Each of these main blocks has a hierarchical structure and consists of at least three types of cortical zones built on top of each other: primary (or projection), where impulses arrive from the periphery or from where impulses are sent to the periphery, secondary (or projection-associative), where the received information is processed or the corresponding programs are prepared, and, finally, the tertiary (or overlap zones), which are the most recently developed apparatus of the cerebral hemispheres and which in humans provide the most complex forms of mental activity, requiring the joint participation of many areas of the cerebral cortex.

Bibliography

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First function block make up analyzers, or sensory systems. Analyzers perform the function of receiving and processing signals from the external and internal environment of the body. Each analyzer is tuned to a specific signal modality and provides a description of the entire set of signs of perceived stimuli. The modal specificity of the analyzer is primarily determined by the characteristics of the functioning of its peripheral formations and the specificity of the receptor elements. However, to a large extent, it is associated with the peculiarities of the structural organization of the central sections of the analyzer, the orderliness of interneuron connections of all morphological formations from the receptor level to the cortical end (projection zones).

Analyzer is a multi-level system with a hierarchical principle of its design. The base of the analyzer is the receptor surface, and the top is the projection zones of the cortex. Each level of this morphologically ordered structure is a collection of cells, the axons of which go to the next level (the exception is the upper level, the axons of which extend beyond the limits of this analyzer). The relationship between successive levels of analyzers is built on the principle of “divergence-convergence”. The higher the neural level of the analyzer system, the greater the number of neurons it includes. At all levels of the analyzer, the principle of topical projection of receptors is preserved. The principle of multiple receptotopic projection facilitates multiple and parallel processing (analysis and synthesis) of receptor potentials (“excitation patterns”) that arise under the influence of stimuli.

Already in the functional organization of the cellular apparatus of the receptor level of analyzers, essential features of their adaptation to adequate reflection of existing stimuli have emerged (specificity of receptors for photo-, thermo-, chemo- and other types of “energy”). Fechner's well-known law about the logarithmic ratio of the strength of the stimulus and the intensity of the sensation was explained in the frequency characteristics of the discharge of the receptor elements. The effect of lateral inhibition in the horseshoe crab's eye, discovered in 1958 by F. Ratliff, explained the method of image contrast, which improves the capabilities of object vision (shape detection). The mechanism of lateral inhibition acted as a universal way of forming selective channels for transmitting information in the central nervous system. It provides the central neurons of the analyzers with selective tuning of their receptive field to certain properties of the stimulus. A neuron located at the output of the receptive field can highlight one sign of a stimulus (simple detectors) or a complex of its properties (complex detectors). The detector properties of a neuron are determined by the structural organization of its receptive field. Neurons-detectors of a higher order are formed as a result of the convergence of neurons-detectors of a lower (more elementary) level. Neurons that detect complex properties form detectors of “super complex” complexes. The highest level of hierarchical organization of detectors is achieved in the projection zones and association areas of the cerebral cortex.

Primary projection zones of the cortex consist mainly of neurons of the 4th afferent layer, which are characterized by a clear topical organization. A significant portion of these neurons have the highest specificity. For example, neurons in the visual areas selectively respond to certain signs of visual stimuli: some - to shades of color, others - to the direction of movement, others - to the nature of the lines (edge, stripe, line slope), etc. However, it should be noted that the primary zones of individual areas of the cortex also include neurons of a multimodal type that respond to several types of stimuli. In addition, there are neurons whose reaction reflects the influence of nonspecific (limbic-reticular or modulating) systems.

Secondary projection zones of the cortex are located around the primary zones, as if building on top of them. In these zones, the 4th afferent layer gives way to the leading place of the 2nd and 3rd cell layers. These neurons are characterized by the detection of complex features of stimuli, but at the same time they retain the modal specificity corresponding to the neurons of the primary zones. Therefore, it is assumed that the complication of the detector selective properties of neurons in the secondary zones can occur through the convergence of neurons in the primary zones on them. The primary visual cortex (17th Brodmann area) contains mainly neurons-detectors of simple signs of object vision (detectors of the orientation of lines, stripes, contrast, etc.), and in the secondary zones (18th and 19th Brodmann areas ) detectors of more complex contour elements appear: edges, limited line lengths, corners with different orientations, etc. The primary (projection) zones of the auditory (temporal) cortex are represented by the 41st Brodmann area (Fig. 4), whose neurons are modally specific and

Rice. 4. Map of cytoarchitectonic fields of the cerebral cortex.

Convexital surface of the cerebral cortex: A - primary fields; b- secondary fields; V- tertiary fields

respond to various properties of sound stimuli. Like the primary visual field, these primary sections of the auditory cortex have a clear receptotopy. Above the apparatus of the primary auditory cortex are built secondary zones of the auditory cortex, located in the outer parts of the temporal region (22nd and partially 21st Brodmann areas). They also consist predominantly of a powerfully developed 2nd and 3rd layer of cells that react selectively simultaneously to several frequencies and intensities: the sound stimulus.

Thus, the main, modality-specific zones of the brain analyzers are built according to a single principle of hierarchical structural and functional organization. Primary and secondary zones, according to I.P. Pavlova, make up central part, or core, analyzer in the cortex, whose neurons are characterized by selective tuning to a specific set of stimulus parameters and provide mechanisms for fine analysis and differentiation of stimuli. The interaction of primary and secondary zones is complex, ambiguous in nature and, under conditions of normal activity, determines a coordinated community of processes of excitation and inhibition, which consolidates the macro- and microstructure of the nervous network engaged in the analysis of afferent flow in the primary projection sensory fields. This creates the basis for dynamic inter-analyzer interaction carried out in the associative zones of the cortex.

Association areas (tertiary zones) The cortex is a new level of integration: they occupy the 2nd and 3rd cellular (associative) layers of the cortex, on which the meeting of powerful afferent flows, both unimodal, multimodal, and nonspecific, takes place. The vast majority of associative neurons respond to generalized features of stimuli - the number of elements, spatial position, relationships between elements, etc. Convergence of multimodal information is necessary for holistic perception, for the formation of a “sensory model of the world”, which arises as a result of sensory learning.

Association zones are located on the border of the occipital, temporal and posterior parietal cortices. The main part of them consists of formations of the lower parietal cortical region, which in humans has developed so much that it constitutes almost a quarter of all formations of the described sensory block of the brain. The work of these parts of the cerebral cortex is necessary not only for the successful synthesis and differentiation (selective discrimination) of stimuli perceived by a person, but also for the transition to the level of their symbolization - for operating with the meanings of words and using them for abstract thinking, i.e. for that synthetic nature of perception, which I.M. wrote about in his time. Sechenov.

In higher animals, mechanisms that highlight the elementary signs of stimuli constitute only the initial link in the mechanism of perception and differentiation of stimuli (specific nuclei of the thalamus and primary zones of the cortex). In the higher sensory (secondary and associative) zones of the cortex, there is a law of decreasing specificity, which is the reverse side of the principle of the hierarchical organization of detector neurons in the specific subcortex and projection zones of the cortex. It reflects the transition from a fractional analysis of particular modal-specific features of the stimulus to the synthesis of more general “schemes” of what is perceived. It is also logical that, despite the decreasing specificity of the higher sensory fields of the cortex (the predominance of multimodal and associative neurons), they are functionally more advanced formations. They perform the function of integrating complex complex stimuli, they are characterized by plasticity, they are subject to “nonspecific” activation by modulating systems (reticular formation, “centers” of actualized needs, etc.).

The mechanisms for distinguishing figures and their spatial organization in monkeys are associated with the associative zones (temporal and posterior parietal) of the cerebral cortex. It is known that monkeys easily learn to distinguish figures by shape, size and their spatial orientation. After extirpation of the inferotemporal cortex, the monkey has difficulty distinguishing figures by their shape, but easily learns to differentiate them by size and orientation. While removal of the occipital-parietal zone of the cortex leads to a disruption of the mechanism of spatial differentiation of figures in relation to the body, as well as a disruption in distinguishing the position and movement of one’s own body in relation to surrounding objects. Data on the physiological role of the temporal and posterior parietal cortex are still scarce. Thus, to clarify the specific function of the inferotemporal cortex and its neural organization, microelectrode studies were carried out on monkeys using a complex stimulus program: a square and a circle were accompanied by motor learning, and a cross and a triangle were used as insignificant stimuli. As a result of the research, three groups of cells were identified: some neurons responded selectively to only one of the four figures used, other neurons responded to two figures, and others responded to all four (without differentiating the significance of the stimulus). From the experiments it followed that these neurons secrete complex features of the visual image regardless of motor learning, while some of them respond to the appearance of a corresponding sensory stimulus, while others respond only when the stimulus is accompanied by an act of attention. Neurons are plastic; their specific response to a sensory “image” is not associated with motor learning and can only change as a result of sensory input.

training. It should be noted that the properties of these neurons are in good agreement with behavioral and clinical data on the role of the inferotemporal cortex in the formation of complex images. Following the hypothesis expressed in 1949 by D. Hebb, it can be assumed that individual neurons of the associative zones of the cortex are connected in various ways and form cellular ensembles that distinguish “sub-patterns”, i.e. corresponding to unitary forms of perception. These connections, as noted by D. Hebb, are so well developed that it is enough to activate one neuron and the entire ensemble is excited. Later, Yu. Konorsky, relying on the classic data of D. Hubel and T. Wiesel about cortical neurons with “simple”, “complex” and “super complex” receptive fields and detecting increasingly complex signs of a visual stimulus, put forward the concept of “gnostic neurons” . He suggested that unitary perception (i.e., recognition of a familiar face at first sight, a familiar voice, a familiar smell, a characteristic gesture, etc.) corresponds not to ensembles of co-excited neurons, but to single neurons - “gnostic neurons” that integrate excitation under the action of complex complex stimuli. Gnostic neurons constitute the main active basis of the highest levels of analyzers, as a result of which the highest levels of analyzers represent, according to Yu. Konorsky, “gnostic zones.” The Gnostic zone can be considered as a kind of card index of Gnostic neurons, in which all the unitary “sub-images” formed in a given individual in the process of sensory learning are presented.

At first, there was no experimental evidence for the concept of gnostic neurons. The basis for Yu. Konorsky’s assumptions was mainly clinical data. However, work soon began to appear, from which it followed that “gnostic neurons” that selectively respond to complex sets of stimuli exist. Cells have been discovered in the frontal lobes of a cat's brain that selectively respond to the appearance of a complex visual stimulus in the visual field. Talking birds have neurons that are selective for the vowel sounds of human speech. Finally, since the 1980s, a series of studies began to appear on the study of the temporal cortex of monkeys. Neurons that highlight certain facial features have been found in the superior temporal gyrus. The neurons of the superior temporal gyrus differed from each other in their gnostic properties. Some neurons responded only when attention was fixed on the object of interest to the monkey, others - when the gaze wandered freely, if the stimulus fell on the retina. Some neurons gave the maximum response to images of a person’s face in frontal view, others - in profile, and others - to part of the face (upper or lower). However, most neurons respond to a three-dimensional image of a face, and not to a two-dimensional one. Some neurons respond to the face of a specific individual, others - to any face, regardless of individual features. Most of the neurons in the superior temporal gyrus turned out to be specific to a specific living person (human or monkey). The formation of the selectivity mechanism in the temporal cortex of the monkey occurs under the influence of individual experience, since there is a dependence of the selective properties of neurons on the circle of people (animals and experimenters) with whom the monkey was in communication before the experiments. Data from neural studies on monkeys on the perception of facial images are consistent with the results of observations of patients with prosopagnosia (impaired recognition of faces), which also indicate the presence in the area of the temporal cortex of the brain of a special recognition mechanism

It is known that the system of neurons that detect complex sensory stimuli (gnostic units) is formed on the basis of an innate (genetically determined) system of cortical neurons with “hard” connections and a large reserve of “labile”, plastic connections. During a certain critical (sensitive) period of ontogenetic development and maturation of interneuron connections, the functional involvement of these potential connections is important. Their actualization is carried out under the influence of external stimulation (individual sensory experience). An additional contribution to the process of acquiring individual experience is made by a modulating system that has a “nonspecific” activating effect on the corresponding analyzer. The activating effect is achieved through orientation-exploratory reflex or attention. This activation process, according to Yu. Konorsky, is a necessary prerequisite for transformation

potential cortical connections into active ones, i.e. makes possible the formation of gnostic neurons, gnostic zones and the cognitive system.

Modulating brain systems

I.P. Pavlov repeatedly returned to questions about the decisive role in the implementation of full-fledged conditioned reflex activity of the optimal tone of the cerebral cortex, the need for high mobility: nervous processes that allow you to easily move from one activity to another. Under conditions of optimal excitability of the cortex, nervous processes are characterized by a certain concentration, balance of excitation and inhibition, the ability to differentiate and, finally, high mobility of nervous processes that determine the course of each organized purposeful activity.

A device that acts as a regulator of the level of wakefulness, as well as carrying out selective modulation and updating of the priority of a particular function, is modulating system of the brain. It is often called the limbic-reticular complex or ascending activating system. The nervous formations of this apparatus include the limbic and nonspecific brain systems with their activating and inactivating structures. Among the activating formations, the reticular formation of the midbrain, the posterior hypothalamus, and the blue spot in the lower parts of the brain stem are primarily distinguished. Inactivating structures include the preoptic area of the hypothalamus, the raphe nuclei in the brain stem, and the frontal cortex.

The most important part of the modulating block of the brain is the activating reticular formation. Phylogenetically, the reticular formation of the brain represents the most ancient morphological formation. Back in 1855, the Hungarian anatomist József Lenhossek described a network of nerve cells located in the middle of the brain stem. The cytoarchitecture of this peculiar mesh structure has not yet been sufficiently studied; it is obvious that the reticular formation is not an amorphous formation. In the reticular formation, more or less compact and limited cell accumulations are distinguished - nuclei, distinguished by various morphological features. In this regard, some authors consider the reticular formation as a diffuse, elongated single formation, while others consider it a complex consisting of many differentiated nuclei with different structures and functions. Laterally (from the sides), the reticular formation is surrounded by sensory pathways. Thus, the fibers of the reticular formation are surrounded by a layer of sensory pathways, which form many collaterals to it.

The functional purpose of the reticular formation remained unknown for a long time. The first indication of the descending inhibitory influences of the reticular formation were the experiments of I.M. Sechenov, in which inhibition of the reflex reactions of the frog was observed upon irritation of the interstitial brain.

V.M. Bekhterev discovered the ascending influences of the reticular formation on the motor area of the cortex, leading to the occurrence of convulsive seizures when certain areas of the pons are irritated. However, only electrophysiological studies revealed the exclusive role of the reticular formation in the integrative activity of the brain. This discovery was made in 1949 by G. Magun and G. Moruzzi. By stimulation through electrodes implanted into the brainstem (at the level of the midbrain), they were able to obtain a reaction to awaken a sleeping animal. G. Magun called this brain stem system ascending activating system of the brain.

The fibers of the reticular formation, moving upward, form modulating “inputs” (usually axodendritic synapses) in the higher-lying brain structures, including the old and new cortex. From the old and new cortex originate descending fibers that go in the opposite direction to the structures of the hypothalamus, midbrain and to lower levels of the brain stem. Through descending systems of connections, all underlying formations are under the control and control of those programs that arise in the cerebral cortex and the implementation of which requires modulation of activity and modification of states of wakefulness. Thus, the activation unit with its ascending and descending influences works (according to the feedback principle) as a single self-regulating apparatus, which ensures a change in the tone of the cortex, and at the same time is itself under its control. This apparatus is used to plastically adapt the body to environmental conditions. It contains at its core at least two sources of activation: internal and external. The first is associated with metabolic processes that ensure the internal balance of the body, the second - with the influence of the external environment. First source of activation is the internal activity of the organism itself, or needs. Any deviations from vital “constants” as a result of changes in nervous or humoral influences or as a result of selective excitation of various parts of the brain lead to the selective “switching on” of certain organs and processes, the combined work of which ensures the achievement of an optimal state for a given type of activity of the body.

The hypothalamus is part of the interstitial brain and contains dozens of highly differentiated nuclei with an extensive and versatile system of connections. Its important anatomical feature is the high permeability of the hypothalamic vessels for large molecular protein compounds. This ensures optimal conditions for metabolism in the neurons of the hypothalamus and obtaining information about the humoral environment of the body. Its versatile regulatory functions are realized humorally and through extensive nerve connections with various areas of the brain.

As part of the brain's activating system, the posterior hypothalamus mediates behavioral activation. This is achieved primarily through the regulation of the autonomic and endocrine functions of the body. Thus, the hypothalamus coordinates the internal needs of the body with its external behavior aimed at achieving an adaptive effect. The hypothalamus is part of the need-motivational system, being its main executive structure. Moreover, it not only participates in the regulation of individual vital functions (hunger, thirst, sexual desire, active and passive defense), but combines them into complex complexes or systems.

Depending on the nature of the nervous and humoral signaling collected in the hypothalamus, it either accumulates or inhibits motivational excitation that determines external behavior (for example, eating). With strong food arousal, sympathetic activation of the cerebral cortex, general motor restlessness, and reproduction of previously learned behavior predominate. Satisfaction of the actualized need is accompanied by the dominance of the parasympathetic system - motor sedation and drowsiness. In ahemispheric animals, stimulation of the need centers of the hypothalamus causes only more general, generalized motivational arousal, manifested in general, non-targeted anxiety, since more complex forms of behavior - search response, object selection and its evaluation - are regulated by overlying structures, limbic formations and the cerebral cortex.

Second source of activation associated with exposure to environmental irritants. Limiting contact with the external environment (sensory deprivation) leads to a significant decrease in the tone (excitability) of the cerebral cortex. Under conditions of severe limitation of sensory information, a person may experience hallucinations, which to some extent compensate for the deficiency of sensory stimulation.

In the apparatus of the ascending reticular formation, a mechanism for converting sensory information into two forms of activation: tonic (generalized) and phasic (local). The tonic form of activation is associated with the function of the lower stem sections of the reticular formation. It generally, diffusely maintains a certain level of excitability in the cortex and subcortical formations. The phasic form of activation is associated with the upper parts of the brain stem, and primarily with the nonspecific thalamic system, which locally and selectively distributes the effects of ascending activation on the subcortical formations, old and new cortex.

It has been established that the cerebral cortex, along with a specific functional contribution, has “nonspecific” activating and inhibitory effects on underlying nerve formations. Cortical influences coming through descending fibers represent a fairly differentiated organization and can be considered as additional third source of activation. Specific bundles of these fibers, which selectively change the excitability of the sensory and motor apparatuses, come from the primary and secondary zones of the cortex. The most extensive activating and inactivating selective influences, projected onto the brainstem, come from the frontal cortex (the source of voluntary activation). These descending fibers, which conduct selective cortical impulses to various formations of the trunk, according to A.R. Luria, are the apparatus through which the higher parts of the cortex are directly involved in the formation of plans and programs of human behavior; with their help, the underlying modulating apparatuses of the thalamic and brain stem are also involved in the implementation of these processes, and thus a sufficient level of activity is ensured for the implementation of complex forms of higher nervous (mental) activity.

Dynamic localization of functions in the cerebral cortex. Three main functional blocks of the brain (Luria A.R.) Associative part of the brain

5.2. PHYSIOLOGY OF THE SPINAL CORD

5.2.1. Structural and functional characteristics

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