Associative apparatus of the brain. Dynamic localization of functions in the cerebral cortex

Based on numerous studies, the functional significance of various areas of the cerebral cortex has been established with certain accuracy. big brain.

Areas of the cerebral cortex that have characteristic cytoarchitectonics and nerve connections involved in performing certain functions are nerve centers. Damage to such areas of the cortex manifests itself in the loss of their inherent functions. The nerve centers of the cerebral cortex can be divided into projection and associative.

Projection centers are areas of the cerebral cortex, representing the cortical part of the analyzer, which have a direct morphofunctional connection through afferent or efferent pathways with neurons of the subcortical centers. They carry out primary processing incoming conscious afferent information and the implementation of conscious efferent information (voluntary motor acts).

Associative centers are areas of the cerebral cortex that do not have a direct connection with subcortical formations, but are connected by a temporary two-way connection with projection centers. Associative centers play a primary role in the implementation of higher nervous activity (deep processing of conscious afferent information, mental activity, memory, etc.).

At present, the dynamic localization of some functions of the cerebral cortex has been clarified quite accurately.

Areas of the cerebral cortex that are not projection or associative centers are involved in inter-analyzer integrative brain activity.

Projection nerve centers The cerebral cortex develops both in humans and in higher vertebrates. They begin to function immediately after birth. The formation of these centers is completed much earlier than associative ones. In practical terms, the following projection centers are important.

1. Projection center of general sensitivity (tactile, pain, temperature and conscious proprioceptive) is also called a skin analyzer of general sensitivity. It is localized in the cortex of the postcentral gyrus (fields 1, 2, 3). It ends with the fibers that run as part of the thalamo-cortical pathway. Each area of ​​the opposite half of the body has a distinct projection at the cortical end of the skin analyzer (somatotopic projection). In the upper part of the postcentral gyrus the lower limb and torso are projected, in the middle - the upper limb and in the lower - the head (Penfield's sensory homunculus). The size of the projection zones of the somatosensory cortex is directly proportional to the number of receptors located in the skin. This explains the presence of the largest somatosensory zones, corresponding to the face and hand (Fig. 3.25). Damage to the postcentral gyrus causes loss of tactile, pain, temperature sensitivity and muscle-articular sensation on the opposite half of the body.

Rice. 3.25.

• 1 – genitals; 2 – foot; 3 – thigh; 4 – torso; 5 – brush; 6 – index and thumb; 7 – face; 8 – teeth; 9 – tongue; 10 – pharynx and internal organs
• 2. Projection center of motor functions (kinesthetic center), or motor analyzer, is located in the motor area of ​​the cortex, including the precentral gyrus and the pericentral lobule (fields 4, 6). In the 3rd–4th layers of the cortex of the motor analyzer, the fibers running as part of the thalamo-cortical pathway end.

Here the analysis of proprioceptive (kinesthetic) stimuli is carried out. In the fifth layer of the cortex there is the nucleus of the motor analyzer, from the neurocytes of which the corticospinal and corticonuclear tracts originate. The precentral gyrus also has a clear somatotopic localization of motor functions. Muscles that perform complex and finely differentiated movements have a large projection area in the cortex of the precentral gyrus. The largest area is occupied by the projection of the muscles of the tongue, face and hand, the smallest area is occupied by the projection of the muscles of the trunk and lower extremities. The somatotopic projection to the precentral gyrus is called the “Penfield motor homunculus.” The human body is projected on the gyrus “upside down”, and the projection is carried out on the cortex of the opposite hemisphere (Fig. 3.26).

Afferent fibers ending in the sensitive layers of the cortex of the kinesthetic center initially pass as part of the Gaulle, Burdach and nuclear-thalamic tracts, conducting impulses of conscious proprioceptive sensitivity. Damage to the precentral gyrus leads to impaired perception of stimuli from skeletal muscles, ligaments, joints and periosteum. The corticospinal and corticonuclear tracts conduct impulses that provide conscious movements and have an inhibitory effect on the segmental apparatus of the brain stem and spinal cord. The cortical center of the motor analyzer, through a system of associative fibers, has numerous connections with various cortical sensory centers (the center of general sensitivity, the center of vision, hearing, vestibular functions, etc.). These connections are necessary to perform integrative functions when performing voluntary movements.

3. Projection center of the body diagram located in the region of the intraparietal sulcus (area 40s). It presents somatotopic projections of all parts of the body. The center of the body circuit receives impulses primarily from conscious proprioceptive sensitivity. The main functional purpose of this projection center is to determine the position of the body and its individual parts in space and assess muscle tone. When the superior parietal lobe is damaged, there is a violation of such functions as recognition of parts of one’s own body, sensation of extra limbs, and disturbances in determining the position of individual parts of the body in space.

Rice. 3.26.

• 1 – foot; 2 – shin; 3 – knee; 4 – thigh; 5 – torso; 6 – brush; 7 – thumb brushes; 8 – neck; 9 – face; 10 – lips; 11 – tongue; 12 – larynx
• 4. projection hearing center, or the nucleus of the auditory analyzer, is located in the middle third of the superior temporal gyrus (field 22). In this center, the fibers of the auditory pathway end, originating from the neurons of the medial geniculate body (subcortical hearing center) of their own and, mainly, the opposite side. Ultimately, the fibers of the auditory tract pass through the auditory radiation.

When the projection center of hearing is damaged on one side, there is a decrease in hearing in both ears, and on the opposite side of the lesion, hearing decreases to a greater extent. Complete deafness is observed only with bilateral damage to the projection centers of hearing.

5. Projection center of vision, or the nucleus of the visual analyzer, is localized on the medial surface of the occipital lobe, along the edges of the calcarine groove (field 17). It ends with the fibers of the optic pathway on its own and opposite sides, originating from the neurons of the lateral geniculate body (subcortical center of vision). There is a certain somatotopic projection of various parts of the retina onto the calcarine sulcus.

Unilateral damage to the projection center of vision is accompanied by partial blindness in both eyes, but in different parts of the retina. Complete blindness occurs only with bilateral lesions.

• 6. Projection center of smell, or the nucleus of the olfactory analyzer, is located on the medial surface of the temporal lobe in the cortex of the parahippocampal gyrus and in the hook. Here the fibers of the olfactory pathway end on their own and opposite sides, originating from the neurons of the olfactory triangle. With unilateral damage to the projection center of smell, a decrease in the sense of smell and olfactory hallucinations are noted.
• 7. Projection center of taste, or the core of the taste analyzer, is located in the same place as the projection center of smell, i.e. in the limbic region of the brain (uncus and parahippocampal gyrus). In the projection center of taste, the fibers of the taste pathway of its own and the opposite side, originating from the neurons of the basal ganglia of the thalamus, end. When the limbic region is damaged, disorders of taste and smell are observed, and corresponding hallucinations often appear.
• 8. Projected center of sensitivity from internal organs, or visceroception analyzer, located in the lower third of the postcentral and precentral gyri (field 43). The cortical part of the visceroception analyzer receives afferent impulses from smooth muscles and mucous membranes of internal organs. In the cortex of this area, fibers of the interoceptive pathway end, originating from neurons of the ventrolateral nuclei of the thalamus, into which information enters along the nuclear-thalamic tract. In the projection center of visceroception, mainly pain sensations from internal organs and afferent impulses from smooth muscles are analyzed.
• 9. Projection center of vestibular functions, undoubtedly has its representation in the cerebral cortex, but information about its localization is ambiguous. It is generally accepted that the projection center of vestibular functions is located in the region of the middle and inferior temporal gyri (fields 20, 21). The adjacent sections of the parietal and frontal lobes also have a certain relationship to the vestibular analyzer. In the cortex of the projection center of the vestibular functions, fibers originating from the neurons of the median nuclei of the thalamus end. Lesions of these cortical centers are manifested by spontaneous dizziness, a feeling of instability, a feeling of falling through, a sensation of movement of surrounding objects and deformation of their contours.

Concluding the consideration of projection centers, it should be noted that the cortical analyzers of general sensitivity receive afferent information from the opposite side of the body, therefore, damage to the centers is accompanied by disorders of certain types of sensitivity only on the opposite side of the body. Cortical analyzers special types sensitivity (auditory, visual, olfactory, gustatory, vestibular) are associated with the receptors of the corresponding organs of their own and opposite sides, therefore, complete loss of the functions of these analyzers is observed only when the corresponding zones of the cerebral hemisphere cortex are damaged on both sides.

Associative nerve centers. These centers are formed later than the projection centers, and the timing of corticalization, i.e. maturation of the cerebral cortex is not the same in these centers. Associative centers are responsible for thought processes, memory and the implementation of verbal function.

• 1. Association center for "stereognosy" ", or the nucleus of the skin analyzer (the center for recognizing objects by touch). This center is located in the superior parietal lobule (field 7). It is bilateral: in the right hemisphere - for the left hand, in the left - for the right hand. The center of "stereognosia" is associated with the projection the center of general sensitivity (postcentral gyrus), from which nerve fibers conduct impulses of pain, temperature, tactile and proprioceptive sensitivity. Incoming impulses in the associative cortical center are analyzed and synthesized, resulting in the recognition of previously encountered objects. Throughout life, the center of “stereognosy” occurs. constantly develops and improves. With damage to the superior parietal lobule, patients lose the ability to create a general holistic idea of ​​an object by touch, i.e., individual properties of objects, such as shape, volume, temperature, density, mass. , are defined correctly.
• 2. Association center of "praxia", or an analyzer of purposeful habitual movements. This center is located in the inferior parietal lobule in the cortex of the supramarginal gyrus (area 40), in right-handers - in the left hemisphere of the cerebrum, in left-handers - in the right. In some people, the center of “praxia” is formed in both hemispheres; such people have equal control of the right and left hands and are called ambidextrous.

The center of “praxia” develops as a result of repeated repetition of complex purposeful actions. As a result of the consolidation of temporary connections, habitual skills are formed, for example, working on a typewriter, playing the piano, performing surgical procedures, etc. As life experience accumulates, the center of praxia is constantly improved. The cortex in the region of the supramarginal gyrus has connections with the posterior and anterior central gyri.

After synthetic and analytical activity is carried out, information from the “praxia” center enters the precentral gyrus to the pyramidal neurons, from where it reaches the motor nuclei of the anterior horns of the spinal cord along the corticospinal tract.

3. Association Vision Center, or visual memory analyzer, is located on the superolateral surface of the occipital lobe (fields 18–19), in the left hemisphere for right-handers, in the right hemisphere for left-handers. It provides memorization of objects by their shape, appearance, color. It is believed that neurons in field 18 provide visual memory, and neurons in field 19 provide orientation in an unfamiliar environment. Fields 18 and 19 have numerous associative connections with other cortical centers, due to which integrative visual perception occurs.

When the visual memory center is damaged, visual agnosia develops. Partial agnosia is more often observed (cannot recognize friends, your home, or yourself in the mirror). When field 19 is damaged, a distorted perception of objects is noted; the patient does not recognize familiar objects, but he sees them and avoids obstacles.

The human nervous system has specific centers. These are the centers of the second signaling system, providing the ability to communicate between people through articulate human speech. Human speech can be produced in the form of the production of articulate sounds ("articulation") and the representation of written characters ("graphics"). Accordingly, associative patterns are formed in the cerebral cortex speech centers– acoustic and optical centers of speech, center of articulation and graphic center of speech. The named associative speech centers are formed near the corresponding projection centers. They develop in a certain sequence, starting from the first months after birth, and can improve until old age. Let's consider associative speech centers in the order of their formation in the brain.

4. Associated Hearing Center, or the acoustic speech center (Wernicke's center), located in the cortex of the posterior third of the superior temporal gyrus. Nerve fibers originating from the neurons of the projection center of hearing (the middle third of the superior temporal gyrus) end here. The associative hearing center begins to form in the second or third month after birth. As the center develops, the child begins to distinguish articulate speech among the surrounding sounds, first individual words, and then phrases and complex sentences.

When Wernicke's center is damaged, patients develop sensory aphasia. It manifests itself in the form of a loss of the ability to understand one’s own and others’ speech, although the patient hears well, reacts to sounds, and it seems to him that those around him are speaking in a language unfamiliar to him. The lack of auditory control over one’s own speech leads to a disruption in the construction of sentences; speech becomes incomprehensible, full of meaningless words and sounds. When Wernicke's center is damaged, since it is directly related to speech formation, not only the understanding of words suffers, but also their pronunciation.

5. Associative motor speech center (speech motor), or speech articulation center (Broca's center), is located in the cortex of the posterior third of the inferior frontal gyrus (area 44) in close proximity to the projection center of motor functions (precentral gyrus). The speech motor center begins to form in the third month after birth. It is one-sided - in right-handed people it develops in the left hemisphere, in left-handed people - in the right. Information from the speech motor center enters the precentral gyrus and further along the cortical-nuclear pathway - to the muscles of the tongue, larynx, pharynx, and muscles of the head and neck.

When the speech motor center is damaged, motor aphasia(loss of speech). With partial damage, speech can be slow, difficult, chanted, incoherent, and often characterized only by individual sounds. Patients understand the speech of those around them.

6. Associative optical speech center, or visual analyzer writing(lexia center, or Dejerine center), is located in the angular gyrus (field 39). The neurons of the optical speech center receive visual impulses from the neurons of the projection center of vision (field 17). In the center of "lexia" there is an analysis of visual information about letters, numbers, signs, the letter composition of words and understanding their meaning. The center is formed from the age of three, when the child begins to recognize letters, numbers and evaluate their sound meaning.

When the “lexia” center is damaged, alexia (reading disorder) occurs. The patient sees the letters, but does not understand their meaning and, therefore, cannot read the text.

7. Association Center for Written Signs, or motor analyzer of written signs (center of the carafe), located in the posterior part of the middle frontal gyrus (field 8) next to the precentral gyrus. The "carafe" center begins to form in the fifth or sixth year of life. This center receives information from the “praxia” center, intended to provide subtle, precise hand movements necessary for writing letters, numbers, and drawing. From the neurons of the carafe center, axons are sent to the middle part of the precentral gyrus. After the switch, information is sent along the corticospinal tract to the muscles of the upper limb. When the “decanter” center is damaged, the ability to write individual letters is lost, and “agraphia” occurs.

Thus, speech centers have a unilateral localization in the cerebral cortex. For right-handers they are located in the left hemisphere, for left-handers - in the right. It should be noted that associative speech centers develop throughout life.

8. Association center for combined head and eye rotation (cortical center of gaze) is located in the middle frontal gyrus (field 9) anterior to the motor analyzer of written signs (center of the carafe). It regulates the combined rotation of the head and eyes in the opposite side due to impulses arriving at the projection center of motor functions (precentral gyrus) from the proprioceptors of the muscles of the eyeballs. In addition, this center receives impulses from the projection center of vision (cortex in the area of ​​the calcarine sulcus - field 17), originating from the neurons of the retina.

37. Association center of the reptile brain

Having examined the general plan of the structure of the nervous system, we should separately dwell on the new principles of organization and functioning of the brain, first implemented in reptiles. The nervous system of archaic amniotes became
a logical development of the structure of a successful amphibious design.
However, the amphibian brain practically performed the function of a complex reflex apparatus, and its intellectual capabilities remained unclaimed. The evolution of amphibians was determined by muscles, teeth, linear dimensions and the scale of reproduction.

There was an elementary development of food resources, where there was neither room nor biological necessity for the development of complex behavior.
We encounter traces of this period of vertebrate evolution when trying to develop conditioned reflexes in various representatives of modern amphibians. Extremely low learning ability and lack of
long-term memory for the accumulation of individual experience show that ancient amphibians never faced complex behavioral tasks in their evolution.
Features of the development of sensory organs and signs of complex behavior in reptiles are based on the features of the structural organization of the brain.

The reptile brain differs from the amphibian brain in both quantitative and qualitative terms. Before the appearance of amniotes, behavioral strategies or reactions to a specific stimulus were selected according to the principle of dominance (see Fig. III-6, f). This principle is that there is no pronounced large association center of the brain in many proto-aquatic vertebrates or amphibians (see Fig. III-6, e). Choice
forms of behavior occur on the basis of comparison of the activities of approximately equivalent parts of the brain serving various sense organs. The level of brain arousal plays a decisive role
analytical centers of one of the analyzers. The representation of the sense organ that has achieved the greatest excitement in the brain becomes the main area for decision making. After choosing one of
instinctive reactions are followed by its behavioral implementation. This process is carried out under the control of the same simple comparison of dominance. If, in the process of carrying out a reaction, a new irritation arises that changes the ratio of excitations of the sense organs,
then the behavioral implementation of the instinctive process stops.
Each specific situation is different from the previous one, but the same set of senses is involved. If the greatest excitation is achieved in the same sensory system, then the behavior is preserved, and if in another, then
changes. Since absolutely identical conditions practically never occur in natural life, the behavior of even the most primitive anamnia will be infinitely varied. Therefore the behavior
each individual will be individual with fairly high dynamic adaptability.

The first signs of an associative center appeared in the brain of amphibians. For them, such a center could become the midbrain or diencephalon. There was every reason for this. In the diencephalon are
neuroendocrine centers that control sexual behavior, migration and the energy balance of the body anamnios. Through the activation of the centers of the diencephalon, instinctive behavior programs are launched that control the work of other parts of the brain. It would seem that the diencephalon could become the analytical center of the behavior of anamnia, and then amniotes. However, in this case, the system for implementing behavioral reactions would consist not only in the work of the nervous system.
Each time, any behavioral event would lead to stimulation of the neuroendocrine centers.

Hormonal regulation of behavior takes a long time to implement, while neurological regulation takes a long time. When changing forms quickly
behavior would result in a conflict between inert hormonal and dynamic neural programs of behavior. In insects, this conflict was resolved in favor of neurohormonal centers and purely
instinctive behavior.
A rather unstable situation has developed with primary aquatic vertebrates and amphibians. On the one hand, the role of hormonal-instinctive regulation of behavior in amphibians is very large and clearly
dominates when choosing behavioral strategies. On the other hand, the neuromorphological substrate is developed quite sufficiently for slight individualization of behavior when implementing these strategies. Arose
an original system of hormonal-dominant selection of forms of behavior from a standard instinctive set. In amphibians, the behavioral strategy is determined by the neurohormonal state of the individual. When implementing
the chosen form of behavior, it adapts to specific conditions using the comparison of dominance, which was described above. In such a scheme for controlling the behavior of anamnia, there is no room for an associative center. It could be needed only when there was a need for rapid adaptive individualization of behavior. This situation can only arise when
the consistent implementation of instinctive forms of behavior will directly depend on the constantly changing situation.
In such unstable conditions environment turned out to be archaic reptiles. Apparently, the requirements for rapid individualization of behavior and memory have increased, and the implementation of the hormonally dominant principle of choosing from a standard instinctive set of behaviors has become ineffective. Arose
a completely new type of decision-making that is preserved in the brains of modern reptiles belonging to distant systematic groups. They are all united by one fundamentally new quality of the brain - a pronounced associative center (see Figure III-7).
The main associative center of reptiles was formed in the roof of the midbrain (see Fig. III-5, c; III-6; III-7, b). It arose on the basis of several sense organs that were represented in this part of the brain. The main part of the midbrain roof is occupied by the visual system. The optic nerves, after passing through the chiasm, cross and ascend to the roof of the midbrain. The axons of the retinal ganglion cells end on the neurons of the roof of the midbrain, which are organized into stratified structures (see Fig. III-5, c; III-7, b).

There is a clear topographical
connection between a certain area of ​​the retina and the roof area of ​​the midbrain. At the same time, the shape of the image and the relative position of its elements are respected. Quite a long front part of the roof
The midbrain was considered exclusively the brain center of the visual analyzer. However, functional and morphological studies have shown that this is far from the case.
Along with the representation of the visual system, information about somatic (skin) sensitivity, motor analyzer, vestibular and auditory signals comes to the roof of the midbrain (see Fig. III-6, e).

The auditory analyzer in reptiles significantly increases its representation in this center. As a result, in many reptiles, inconspicuous paired chambers appear in the posterior part of the roof of the midbrain.
protrusions - posterior or lower tubercles. The roof of the midbrain becomes not a homogeneous anatomical formation, like in anamnias, but a quadrigeminal. It concentrates representation practically
all major remote and contact analyzers. Even the olfactory system has its representation in the roof of the midbrain. With the exception of the olfactory system, almost all sensory projections to the roof of the midbrain in reptiles are topological in nature. This
means that information from each specific part of the body is presented in a strictly defined area of ​​the roof of the midbrain.
The principle of a body map is preserved, which is transferred pointwise to the brain.
Thus, in the roof of the midbrain of reptiles a variety of information is concentrated about the state of one’s own body and the surrounding world, which is combined according to a topological principle.
Consider what happens in the roof of the midbrain if the front right limb of a reptile simply stands on an unusual surface. When assessing such a situation in the roof of the midbrain, comparative analysis somatic, sensorimotor, auditory and visual information.
This is easy to do because all the signals are concentrated in one center, and often on top of each other, like in a layer cake. The midbrain conducts a complex analysis of many factors of one phenomenon, which
allows you to choose the most appropriate response. The stratified structure of the midbrain roof is ideal for this.
Extremely simplifying the real situation, we can say that in the roof of the midbrain, the representation of various sensory systems is located on conditional “floors” organized in the horizontal plane. Each floor is occupied by a unique map. It can be a momentary information map of receptor signals from the surface of the body, an image on the retina, or an acoustic field. All
these maps are oriented on their “floors” so that they reflect approximately the same direction in space.

The auditory signal from the anterior right limb lies under its visual map and above the somatic
signal from the skin of the foot. Specialized “floors” are related to each other using vertical connections, which allow you to quickly assess a specific situation and make an adequate decision. This diagram
The work of the roof of the midbrain allows us to understand the reflex speed of the reptile brain. Apparently, it was this speed that became the main reason for evolutionary success
archaic reptiles.
The emergence of a perfect reflex decision-making center in reptiles led to several important consequences. On the one hand, the ability to quickly select solutions is meaningless if the general
your metabolic rate will remain the same. Consequently, the development of the midbrain was accompanied by an increase in metabolism. On the other hand, an increase in the size of the midbrain roof created
a necessary cellular substrate for memory development. The individual experience of the animal became the basis for comparison of events separated in time. It is difficult to overestimate this event. For the first time real
a basis for individualizing behavior based on comparison of different events. It should be noted that these neurobiological advantages of the reptilian brain are usually not even considered when
reconstructing the early evolution of amniotes (Carroll, 1982).

Archaic reptiles, following the development of the center of reflexological analysis, received a material substrate for remembering various events. They have access to the reproduction of individual experience, which serves as the basis for learning. Amphibians could no longer compete with self-learning archaic reptiles. The hormonal-instinctive principles of behavior of amphibians, fish and invertebrates made them food for reptiles with a developed reflex-associative midbrain.
All of the listed advantages of the structure of the reptile brain could not arise by themselves. For such a deep qualitative restructuring of the brain, extremely tough and
extraordinary conditions. Archaic reptiles had to find themselves in a unique environment with very high demands on the analytical properties of the brain and individual memory.

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 the 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.

Different areas of the cortex are divided, depending on the function performed, into projection (somatosensory, visual, auditory), motor and associative (prefrontal, parieto-temporo-occipital, limbic) (Fig. 9.1). The somatosensory cortex occupies the postcentral gyri of the brain, located directly behind the central sulcus, and in front of this sulcus, i.e., in the precentral gyri, is the motor cortex (the premotor area is located in front of it).

The primary visual or striate cortex occupies the medial part of the occipital lobes (area 17 according to Brodmann), the primary auditory cortex is located in the depth of the lateral or Sylvian fissure (area 41). Information from the vestibular apparatus necessary to maintain balance enters the postcentral gyrus. There, in the area of ​​​​the tongue, signals from taste buds are processed. The primary projection areas are adjacent to the secondary ones, and the entire remaining surface of the brain is represented by the associative cortex, which occupies most of its surface.

From the endings of sensory neurons located on the surface of the body, as well as in the muscles and tendons, information about touch and pressure on the skin, about the action of temperature and pain stimuli, about changes in the length and tension of various muscles is received along parallel pathways to the cortex. At each switching point, the transmitted signal is processed; each such information flow arrives at a specific area of ​​the sensory cortex, where a synthesis of a holistic sensation should occur from the disparate characteristics of the stimulus. Where and how does this happen?

In the 30s of the twentieth century, in experiments on monkeys it was shown (W. Marshall) that action potentials naturally arise in the cerebral cortex in connection with irritation of the body surface. A correspondence was found between different parts of the body and the surface of the cerebral cortex, which made it possible to map the spatial representation of the body in the cerebral cortex.

In 1937, neurosurgeon Wilder Penfield W., together with his colleagues, operated on many patients with epilepsy and, in order to detect the pathological focus of excitation that causes epileptic attacks, dosed electric shock irritated the surface of the brain. Since the operations were performed under local anesthesia, the patients remained conscious and could talk about their sensations associated with electrical stimulation of the cortex. Irritation of different parts of the postcentral gyri of the brain caused a sensation of touching a certain place on the opposite half of the body. This area was called the somatosensory cortex or S 1. The research carried out at the Penfield Clinic was summarized by a map of the somatosensory representation in the cortex - the sensory homunculus, i.e. the little man (Fig. 9.2).

Its proportions do not correspond to those of the human body, since the hands, face, lips and tongue are represented over a larger area of ​​the cortex than the entire body. This disproportion reflects the relative density of sensory innervation: it is much higher in those parts of the body that make it possible to distinguish especially tactile sensations and very small changes in muscle activity. A similar diagram of the motor homunculus was obtained by comparing contractions of various muscles in response to electrical stimulation of certain areas of the motor cortex of the contralateral, i.e., opposite hemisphere in the region of the precentral gyrus (See Chapter 10).

Penfield's original scheme was further refined through studies of the cortex using point microelectrodes, which made it possible to record the activity of individual neurons depending on the nature of the stimuli acting on a limited area of ​​the body surface. This technique made it possible to divide the entire somatosensory cortex into four areas (Fig. 9.3), occupying, in accordance with the division of the cortex according to Brodmann, fields 3a, 3b, 1 and 2. Field 3a receives information from receptors of muscles and joints, field 3b - from superficial skin receptors: this information contains the most basic characteristics of the stimulus. In field 1, further processing of information received from skin receptors occurs, and in field 2 it is combined with that which contains information about muscles and joints. Thus, if elementary ideas about the stimulus are formed in fields 3a and 3b, then complex ones are formed in fields 1 and 2.

All four fields receive information from the general surface of the body, but in each field one of the sensations dominates over the others: in field 3a - this is the input from stretch receptors, in 3b - from superficial skin receptors, in field 2 - from receptors that respond to strong pressure , and in field 1 – from quickly adapting skin receptors. In fields 3a and 3b there are no cells that perceive information about the direction of action of the stimulus and its location. Such neurons are contained in fields 1 and 2, and only with their participation is it possible to determine the three-dimensional shape of an object, that is, to form a spatial sensation, and also to establish the direction in which the stimulus moves across the skin. From some neurons of fields 3a and 3b, axons are directed to fields 1 and 2, where they converge on the same cells, which allows the latter to respond to various complex features of the stimulus, for example, to its contour.

Due to the convergence of various afferent inputs to neurons of areas 1 and 2, their receptive fields are larger than those of neurons 3a and 3b. So, for example, while receptive fields 3a and 3b typically include one finger and one or two knuckles, receptive fields 1 and 2 include multiple fingers, consistent with convergence from multiple regions 3a and 3b. Thus, the sequence of information processing in the somatosensory cortex consists of the organized spread of excitation from many neurons responding to elementary signs of the stimulus to fewer neurons that integrate all elementary signs into a complex.

From each area of ​​the skin, information is received not by an individual neuron of the somatosensory cortex, but by a population of cells whose receptive fields include this area. Some neurons respond to touch, others to constant pressure, others to movement on the skin, etc. Cells that specialize in processing information from certain receptors are combined into cortical columns. Vernon Mountcastle W., who studied this issue in the 50s of the twentieth century, first unsuccessfully tried to find a relationship between different types of receptors and neurons of any of the six layers of the cortex. Afterwards, he was able to establish that the functional associations of cortical neurons do not occur horizontally, that is, within one layer, but vertically, through all six layers of the cortex: such an association was called a column.

The diameter of the cortical columns is approximately 0.2 - 0.5 mm, its neurons are excited predominantly by receptors of one type. This is facilitated by the anatomical organization of the endings of the thalamic neurons that deliver information to the column. The axonal branches of thalamic neurons end mainly within the same column. This organization of the column allows us to consider it an elementary functional unit. The columnar organization is found not only in the somatosensory cortex, it is characteristic of the cortex as a whole - this is the fundamental principle of its organization.

In addition to the primary somatosensory cortex S 1, there is a secondary somatosensory cortex or S 2, which is located on the upper wall of the lateral (Sylvian) fissure, separating the parietal and temporal lobes. Most of the inputs to the secondary sensory cortex are formed by cells of the S 1 areas from both hemispheres, and therefore both halves of the body are represented in the S 2 areas. Outputs from the primary sensory cortex, as well as from the secondary - S 2, are directed to the adjacent regions of the parietal cortex - these are associative areas that integrate all sensory functions. In addition, from field 2 there is an exit to the primary motor cortex, which is of great importance for the implementation of precise movements.

Information to the visual cortex comes from the retina, where, in response to the action of light quanta, hyperpolarizing receptor potentials of its photoreceptor cells - rods and cones - arise, which excite ganglion cells through bipolar cells. The long axons of ganglion cells form optic nerves. Each ganglion cell has its own rounded receptive field, consisting of two antagonistic zones: central and peripheral. One of them is excited when light hits the photoreceptors (on-cells), the other when it is darkened (off-cells) - thus, each receptive field perceives the contrast between the illuminated and darkened areas of the visual field (Fig. 9.4). In approximately half of the receptive fields, on-cells are located in the center, and off-cells are located on the periphery; in the other half of the receptive fields, these zones change places. With the participation of inhibitory cells that carry out lateral inhibition, the retina identifies such signs of an object in the field of view as shape, color and nature of movement. These submodalities are processed in parallel.

The optic nerves coming from the retina partially cross and transmit information to the lateral geniculate body, which is an integral part of the thalamus; with this switching, the principle of retinotopic organization is preserved. From here, information is transmitted to the primary visual cortex, and signals arrive to the input stellate cells of layer IV of the primary visual cortex, and from them to nearby pyramidal neurons, which are called simple because they are activated by linear stimuli of a certain orientation, perceived by the photoreceptor cells of the retina (Fig. 9.5).

Here, the retinotopic principle is still observed, i.e., certain receptive fields of the retina correspond to a general receptive field formed by simple neurons of the visual cortex. However, this field does not have the round shape characteristic of the retina, but an elongated shape, which contains both on- and off-sensitive cells that respond either to the appearance of light or to its disappearance.

If the receptive field of the retina is uniformly illuminated, then simple cortical neurons are not active. When a stimulus appears in the visual receptive field in the form of a light stripe on a dark background or a dark stripe on a light background, or in the form of an edge between light and dark, simple neurons are activated. Different receptive fields formed by simple cells of the visual cortex differ in their ability to respond to a certain inclination of a stripe that appears in the visual field. There are about 20 populations of simple neurons, differing from one another in that they respond to different angles of inclination of a linear stimulus: some to vertical, others to horizontal, and others to those inclined at different angles. Each population distinguishes the angle of inclination of the stimulus within about 10° - it gives the strongest response to a certain (“its”) angle of inclination.

If simple neurons of the visual cortex are located in layer IV, then cells of a different type - complex neurons - have chosen layers 2, 3, 5 and 6 of the cortex. Some of the complex neurons are activated by input stellate cells from layer IV, but most of them receive information from nearby simple neurons adjacent to layer IV. Complex neurons have the same ability as their simple neighbors to produce a particularly strong response to a linear stimulus with a certain angle of inclination. But their receptive field is significantly larger than that of simple neurons, since several simple ones converge to one complex neuron at once. In addition, complex neurons attach almost no importance to clear boundaries between light and dark: within their large receptive field, the on- and off-zones no longer play an important role. But many complex cells specialize in processing information about the nature of the movement of the stimulus: for example, some are more strongly activated when an object appears in the field of view, others when it leaves it. As a result of the joint activity of simple and complex cells, the contours and shape of a complex object are determined.

Simple and complex cells with similar properties, i.e., preferring a certain angle of inclination of a linear stimulus, are combined into vertical columns (Figure 9.6).

Each column, oriented to a certain stimulus inclination, in its IV layer has concentric receptive fields, and above and below them a homogeneous population of simple neurons. Simple neurons transmit information to complex cells from their column; there are also inhibitory neurons in the column. The column, oriented to a certain angle of inclination of the stimulus, has a diameter of about 30-100 µm. The columns adjacent to it are oriented at a different angle of inclination, differing by approximately 10°. Adjacent columns, arranged radially, form a supercolumn or module. It contains a set of columns necessary for orientation within 360°, as well as inserts of neurons located between them that specialize in processing information about the color characteristics of the stimulus. Such cells can be detected by the high concentration of the mitochondrial enzyme in them - cytochrome oxidase; these cells are absent in layer IV, and the term blobs is used to designate their accumulations.

More than half of the complex neurons of the retinotopically organized visual cortex respond to information from both eyes, in each of which the corresponding receptive fields occupy the same position. For such binocular cells, it is important that one eye confirms what the other sees; they are more excited when both eyes are stimulated. Most binocular cells exhibit ocular dominance: they respond more strongly to signals from one eye than from the other. Signals from each eye, alternating, arrive at the cells of layer IV independently of each other.

Adjacent oriented columns have horizontal connections among themselves. These connections ensure synchronized excitation of cortical cells, which is very important for the integration of processed information and the connection of data from individual receptive fields into a coherent image. However, the primary visual cortex is only the first stage of information processing, which continues beyond this area.

The secondary visual cortex consists of many functionally distinct regions: outside the striate cortex, 31 regions have been found in monkeys (possibly even more in humans) related to the processing of visual information. All these areas of the cortex are closely connected with each other, over 300 connecting paths have been identified between them, along which the flow of information moves mainly from regions performing simpler operations to complex ones, in which the next stage of integration occurs.

Relatively recently, using positron emission tomography, it was found that the secondary prestriate cortex, adjacent to the primary visual cortex, appears to be involved in the formation of color sensation and the perception of moving objects. Two main pathways pass through it from the primary visual cortex: ventral and dorsal (Fig. 9.7).

The ventral path passes to the lower part of the temporal lobe, the neurons of which have very large receptive fields and no longer have a retinotopic organization: here the visual stimulus is recognized, its shape, size and color are established. In addition, about 10% of the cells in this area selectively respond to the appearance of hands and faces in the visual field, and in the recognition of hands important role the position of the fingers plays a role, and when recognizing a human face, some neurons are especially active when it is turned to the front, and others when it is turned to the profile. Damage to these areas can lead to prosopagnosia (from the Greek prosop - face; gnosis - knowledge; a - designation of negation), when a person ceases to recognize familiar faces.

In the middle temporal gyrus, as well as in the region of the superior temporal sulcus, there are neurons necessary for the perception of moving objects. This function plays a very important role in the behavior of most animals, and humans and developed primates, with the participation of this area of ​​the cortex, are able to fix attention on stationary objects. The information obtained about the movement of visible objects is also used to carry out voluntary tracking movements of the eyes and for orientation in space during one’s own movement.

The dorsal pathway from the primary visual cortex passes through the dorsal extrastriate cortex to the posterior parietal areas. Its functional significance is to determine the relative position of all visual stimuli. Damage to this area of ​​the cortex is accompanied by a miss when the patient intends to take an object with his hand, although he sees this object and is able to accurately describe its shape and color. Thus, if the ventral pathway from the visual cortex leads to an answer to the question “what” an object is, then the dorsal one relates to the question “where” it is.

9.4. Auditory cortex

The primary auditory cortex in each hemisphere is located deep in the Sylvian fissure, which separates the temporal lobe from the frontal and anterior parietal lobes (area 41). It is surrounded by the secondary auditory cortex. The primary auditory cortex receives information from hair cells located in the inner ear. Depending on their location in the cochlea, hair cells exhibit selective sensitivity to a sound signal of a certain frequency in the range from 20 to 16000 Hz, i.e. different hair cells are “tuned” to a certain tone, to a certain pitch (encoding information based on the principle of localization receptors).

Information about the intensity of a sound stimulus is encoded by the frequency of impulses from the hair cells corresponding to this stimulus. If a sound contains several frequencies, then several groups of receptors and afferent fibers are activated. The auditory tract is quite complex, it includes from five to six neurons, which have numerous return collaterals and transmit signals from one side to the other. When processing signals in the auditory tract, the tonotopic organization is preserved.

The cortical columns of the auditory cortex are also organized tonotopically: the neurons that form them are tuned to one specific tone. In the anterior areas of the auditory cortex there are speakers “tuned” to high tones, and behind them there are speakers that receive information about lower tones. In parallel with the processing of information about pitch, signals about sound intensity and time intervals between individual sounds are processed in neighboring columns of the same area of ​​the cortex.

For individual neurons of the auditory cortex, the strongest stimuli may be sounds of a certain duration, repeated sounds, noise, i.e., sound stimuli with a wide range of frequencies. Neurons of this kind are simple. Along with them, there are complex neurons, the stimuli for which can be certain frequency or amplitude modulations of sounds, different frequency threshold minima. The same principle of information processing is observed here as in the visual cortex: from recording elementary signs of a stimulus (simple neurons) to the formation of an auditory image (complex neurons).

Most neurons in the auditory cortex are activated by signals from the contralateral, i.e., opposite ear, but there are also those that are activated by signals from the ipsilateral ear, i.e., located on the same side. Some neurons receive information from both ears, which is of particular importance for the formation of binaural hearing, which allows one to establish the position of the sound source in space. In general, in the auditory cortex, the same principle of information processing is observed as in the visual cortex: simple neurons serve as detectors for determining the various components of the sound signal, and complex neurons carry out their synthesis, necessary for holistic perception.

Complete bilateral damage to the auditory cortex, hidden in the depths of the Sylvian fissure, is very rare in humans; moreover, with such damage, the surrounding tissue always suffers. In such cases, word deafness usually develops, in which the ability to understand the meaning of words is impaired. Surprisingly, after bilateral damage to the auditory cortex, experimental animals do not show a deficit in tone perception, but the discrimination of one tone from another and the determination of the side, left or right, on which the sound source is located worsens.

Here there is an integration of various sensory functions, primarily somatosensory, visual and auditory; this associative area is especially associated with cognitive processes - thinking and speech, although both require the joint activity of many regions of the cortex, and not just associative fields. The association cortex is organized like sensory projection areas: its neurons are organized into vertical columns.

The posterior part of the parietal cortex (areas 5 and 7) receives information from the somatosensory, visual (dorsal pathway), and auditory cortices (Figure 9.8).

Combining this information makes it possible to navigate the world around us and relate it to our own body, as well as to individual parts of the body: all this can be called spatial sensation. In this case, the functional significance of the left and right posterior parietal areas is not the same, as can be judged by the consequences of damage to the left or right half.

Damage to the dominant half, which in most people is the left, can lead to problems with speech and writing, and sometimes to the loss of the ability to distinguish between the left and right sides and recognize the shape of objects by touch. When the non-dominant, in most cases the right half, is damaged, there are usually no speech impairments, but the sensory connection with the left half of the body is almost lost, although sensory sensitivity is preserved there. Such patients essentially ignore their left half, for example when dressing or when washing, and sometimes they may not recognize their own left arm or leg.

This attitude extends not only to the left half of the body, but also to the left half of the surrounding world. The self-portraits of the artist Anton Röderscheidt are well known, who, after suffering a stroke in the right posterior parietal region, depicted only the left half of his face. But the French cartoonist Sabadell suffered a stroke that damaged the left posterior-parietal region and the artist lost speech, and his right arm was paralyzed. He learned to work with his left hand, regained his skill and even his own style, and, unlike Röderscheidt, he correctly conveyed perspective and space.

The reason for ignoring the left half of the body in people with damage to the right posterior parietal region is the loss of conscious control over it and a characteristic change in memory, when the patient neglects not only real objects on the left, but also memories of these objects. To form a sensation, he needs to transfer his attention to one or another object.

Studies performed using positron emission tomography have shown that changes in the direction of attention in healthy people are associated with activation of the posterior parietal as well as the frontal cortex. However, each of these areas solves different problems associated with the distribution of attention. The parietal region is activated when there is only a switching of attention from one sensory signal to another, and whether this then leads to motor activity or not does not matter. In contrast, the frontal cortex becomes active only when a shift of attention is accompanied by an associated movement.

When patients with damage to the posterior parietal areas of the cortex simultaneously see two visual stimuli, one of which appears in the left and the other in the right visual field, they usually cannot remember the stimulus that appeared on the side opposite to the damage. The use of positron emission tomography when comparing such patients with healthy people made it possible to identify the different importance of the left and right hemispheres in the distribution of attention in space. It turned out that the right hemisphere can control attention in both the left and right visual fields, while the left hemisphere can only do this in the right visual field. Thus, when maintaining attention on objects located in the right visual field, both hemispheres are active, and when transferring it to objects presented in the left visual field, only the right hemisphere exercises conscious control. The right posterior parietal region shows two distinct control regions, while the left region shows only one.

Studies of the electrical activity of individual neurons in the posterior parietal cortex have been conducted in monkeys. At the moment when a light signal appeared in the field of view and the monkey switched its attention to it, the activity of some neurons became maximum and remained this way as long as the animal was interested in this object. If the monkey ignored the signal that appeared in its field of vision, the activity of these neurons was significantly less. These and some other studies have led to the conclusion that it is the activity of neurons in the posterior parietal cortex that determines the direction of attention necessary for manipulating an object. After the monkey fixes its attention in order to better study the object that has aroused its interest, neurons in other areas of the brain that are involved in hand-eye coordination, for example, cells of the frontal cortex.

9.6. Prefrontal association cortex

In the cortex of the frontal lobes, motor and associative areas are distinguished. The anterior central gyri is occupied by the primary motor cortex. Immediately in front of it, on the lateral surface of the frontal lobes, are two regions of the secondary motor cortex: the accessory motor area and the premotor cortex. Ventral to the accessory cortex, in the cingulate gyrus, two more areas of the secondary motor cortex are found. The secondary motor cortex receives most of its afferent signals from the associative cortex, and transmits its signals primarily to the motor cortex.

The entire remaining surface of the frontal lobes is occupied by the association cortex, which is divided into two large regions: the prefrontal and orbitofrontal cortex. The prefrontal cortex is located dorsolaterally, and the orbitofrontal cortex occupies the medial and ventral parts of the frontal lobes and belongs to the limbic association cortex. The primary function of the prefrontal cortex is to formulate plans for executing sets of motor actions.

The prefrontal region receives most of the information necessary for voluntary activity from the posterior parietal association cortex. After the integration of sensory information occurs in the posterior parietal areas of the cortex different types, first of all, somatosensory with visual and auditory activation of the prefrontal cortex begins, which is connected to the posterior parietal areas by numerous intracortical and subcortical connections, for example, through the thalamus. Thanks to this, the prefrontal cortex receives a complete spatial map of the objects in the field of view. Information about external space is combined here with information about the position of the body and its individual parts, and the prefrontal cortex includes all this data in short-term working memory. On this basis, a plan for upcoming actions is created, i.e., from the many possible options for activity, the necessary ones are selected and in the most rational sequence. First of all, the position of the eyes directed to the desired object is programmed, coordination of the actions of both hands is provided, etc. Most of the signals emerging from the prefrontal cortex enter the premotor area of ​​the cortex.

The prefrontal cortex is characterized by an abundance of dopaminergic endings. Dopamine here apparently plays the role of a modulator necessary for maintaining short-term working memory. After a local injection into the prefrontal region of a substance that selectively disrupts dopaminergic transmission, the choice of the correct actions that the monkey must perform in order to get to food worsens.

The development of schizophrenia is associated with disturbances in the dopaminergic system: in most schizophrenics, the size of the frontal lobes is smaller than in healthy people. When solving problems related, for example, to sorting playing cards According to the proposed instructions, in normal people, blood flow increases in the frontal areas, which indicates increased neuronal activity. In schizophrenia, blood flow in the frontal lobes also increases, but significantly less than in healthy people. Patients begin sorting exactly according to the instructions, but soon stop following them, although they can easily repeat the instructions. If you ask them to press a button with their right hand when turning on a light bulb of one color, and with their left hand when turning on another, then, after following the instructions correctly several times, they get confused and either press only one button in response to different signals, or press different buttons in random order. It is noteworthy that here they do not forget the instructions and can repeat them at any time. This suggests that it is not a disorder of long-term memory that leads to deterioration in performance, but a disruption of the interaction between the parieto-temporo-occipital and prefrontal regions.

The limbic cortex includes the medial and ventral surfaces of the frontal lobes (since they are adjacent to the orbits, they are also called the orbital or orbitofrontal cortex), part of the medial surface of the occipital lobes, cingulate gyrus in the depths of the interhemispheric fissure, as well as the anterior surface of the temporal lobes. The limbic cortex interacts with the limbic system of the brain (Fig. 9.9), which consists of a number of interconnected structures located in the midline around the thalamus like its border (limbus - border, edge).

The limbic system includes the amygdala, a group of nuclei in the anterior part of the temporal lobes. Behind them, in the middle part of the temporal lobes, is the hippocampus, adjacent to the lower part of the thalamus. The hippocampus is joined by the fornix, a large collection of fibers that represents the most important pathway of the limbic system: it runs along the dorsal surface of the thalamus forward, to the mamillary bodies and the septum. Several bundles of nerve fibers connect the septum and mamillary bodies with the tonsils and hippocampus and give the limbic system a circular shape, which was first noticed in 1937 by James Papez J.W. On the inner surface of the hemispheres there are two gyri, which are usually referred to as the limbic system: the cingulate and parahippocampal, the first of which encircles the thalamus on the dorsal side, and the second on the ventral side.

The limbic cortex receives information from secondary sensory areas and plays a very important role in the formation of motivations and emotions and the formation of long-term memory. The orbitofrontal cortex, which is part of the limbic association cortex, has direct connections with the amygdala; on the other hand, it influences the creation of a plan for future actions. These connections largely determine the emotional aspects of behavior. When the frontal lobes are damaged, the formation of motivation is disrupted and it becomes difficult to predict the results of actions; such patients are characterized by short temper, are rude in communicating with other people and, at the same time, frivolous.

9.8. Temporal cortex

As already mentioned, this is where the primary and secondary auditory areas are located. When Penfield stimulated the primary auditory cortex during neurosurgery, patients experienced rudimentary acoustic sensations. Irritation of the secondary auditory areas located in the superior temporal region was accompanied by a sensation of rustling or noise, and many patients associated them with previously heard sounds. The inferior regions of the temporal lobes are essential for visual processing, and damage to them has been shown in monkeys to impair the memory-reliant learning process of some tasks. Thus, information processing in the temporal cortex is associated with the use of memory of past experiences.

After removing certain areas of the temporal cortex and hippocampus (to eliminate epilepsy), patients developed impairments in certain types of long-term memory. Memory impairment was more profound if the surgery was bilateral. When only the left temporal region was damaged, patients were worse able to remember the list of nouns presented to them than before the operation, and when the right temporal region was damaged, verbal memory remained almost unchanged, but patterns of drawings were remembered worse. geometric shapes, human faces. Since then, it has been generally accepted that the temporal cortex is related to memory formation.

Using two output electrodes lying on the surface of the cerebral cortex, it is possible to register biopotentials arising with a frequency from 1 to 50 Hz. It is also possible to observe changes in bioelectrical activity through monopolar recording, when the active electrode is located on the surface of the cortex, and the reference electrode is at some distance from it, for example, on the earlobe. The recording obtained under such lead conditions is called an electrocorticogram.

Fluctuations in biopotentials associated with changing activity of cortical neurons can be recorded using electrodes attached to the scalp. The recording obtained in this way is called an electroencephalogram (EEG). In everyday practice, electrodes on the head are placed according to standard patterns, which make it possible to judge changes in bioelectrical activity both between each pair of such electrodes (bipolar leads) and at individual points (monopolar leads). In the latter case, an indifferent electrode is attached to the earlobe or mastoid process, where the electrical processes are so insignificant that they can be taken as zero.

The electroencephalogram reflects changes in the activity of cortical neurons; its pattern depends on the location of the electrodes and the level of wakefulness. In an actively awake person, the EEG is dominated by the so-called. b-rhythm, which is characterized by a low amplitude of recorded potentials at a relatively high wave frequency - from 13 to 26 Hz. During relaxed wakefulness, when a person lies with his eyes closed, the b-rhythm begins to alternate with the a-rhythm, which has a higher amplitude and lower frequency (8-12 Hz). This change is called rhythm synchronization; it is caused by the rhythmic effect on the cortex of some thalamic nuclei.

If a stimulus causing an indicative reaction is applied and a person opens his eyes, then on the EEG the a-rhythm is immediately replaced by the b-rhythm: this phenomenon is called a-rhythm blockade (Fig. 9.10). Thus, the electroencephalogram allows one to observe not only the spontaneous electrical activity of the cortex, but also the neural processes associated with various types activities.

Summary

The cerebral cortex contains significantly more neurons compared to other regions of the brain. In most of the cortex, neurons are grouped so that six alternating layers can be distinguished. Afferent information entering the cortex from the thalamus is transmitted predominantly to input neurons of layer IV, and output neurons are contained mainly in layer VI. The inputs to the cortex are organized in such a way that the processing of similar signals is carried out by a population of neurons located in all six layers and forming a vertical column, and homogeneous columns are combined into a module. The most important principle of information processing in the cortex is that cells performing elementary functions transmit signals to complex neurons, and from different types complex neurons, information is collected in certain regions of the associative cortex. Three association areas of the cortex are involved in various cognitive functions, such as the formation of sensations, the formation of emotions, the planning of conscious actions, the emergence of long-term memory, and the generation of speech. Although each of the association areas specializes in specific tasks, they are all involved in most cognitive functions because such activities require integrative activity from different brain regions.

Questions for self-control

130. Axons of which cells form the optic nerve?

A. Photoreceptor; B. Bipolar; V. Ganglionic; G. Neurons of the thalamus; D. Neurons of the lateral geniculate body.

131. What visual stimulus leads to activation of the receptive fields of simple neurons in the primary visual cortex?

A. Uniform illumination of the field; B. Uniform darkening of the field; B. Stimulus movement; D. Object color; D. The line between light and dark.

132. In which layer of the primary visual cortex are simple neurons concentrated?

A. II; B. III; V. IV; G. V; D.VI.

133. To what area of ​​the cortex is the ventral pathway, starting in the primary visual cortex, directed?

A. Prefrontal cortex; B. Limbic cortex; B. Posterior parietal cortex; G. Inferotemporal region; D. Somatosensory cortex.

134. The connection of which areas of the cortex is especially important in determining the location of an object in the visual field?

A. Visual – somatosensory; B. Visual – prefrontal; B. Visual – inferotemporal; D. Visual – middle temporal; D. Visual – posterior parietal.

135. In which field is the primary auditory cortex located?

A. 5; B. 7; V. 17; G. 39; D. 41.

136. After damage to which area of ​​the cortex can half-body neglect syndrome develop?

A. Left somatosensory area; B. Right somatosensory area; B. Right posterior parietal cortex; D. Left prefrontal region; D. Right motor area.

137. Activation of which area of ​​the cortex is required in order to transfer attention from one object to another?

A. Primary visual cortex; B. Secondary visual cortex; B. Inferotemporal region; G. Middle temporal region; D. Posterior parietal region.

138. Which of the following is not true of the frontal lobes of the brain?

A. Somatosensory cortex; B. Premotor cortex; B. Accessory motor area; D. Orbitofrontal cortex; D. Primary motor cortex.

139. With the interaction of which two areas, a plan for upcoming actions is created?

A. Primary visual cortex - extrastriate areas of the cortex; B. Primary visual cortex - posterior parietal region; B. Secondary motor cortex - primary motor cortex; D. Somatosensory cortex - primary motor cortex; D. Posterior parietal region - prefrontal cortex.

140. After a local injection of certain substances into the prefrontal cortex, a disruption occurred in the sequence of actions that allowed the monkey to get to food. In which neurotransmitter system do these substances disrupt signal transmission?

A. Glutamate; B. GABA; B. Adrenaline; G. Dopamine; D. Acetylcholine.

141. When what area of ​​the cortex is damaged, short-term working memory, necessary for performing a certain sequence of actions, is impaired?

A. Prefrontal; B. Orbitofrontal; B. Primary motor cortex; D. Somatosensory cortex; D. Temporal.

142. Which of the following is not true of the limbic cortex?

A. Dorsal surface of the frontal lobes; B. Medial surface frontal lobes; B. Ventral surface of the frontal lobes; G. Anterior surface of the temporal lobes; D. Cingulate gyri.

143. Which of the following does not belong to the limbic system?

A. Tonsils; B. Hippocampus; B. Arch; G. Corpus callosum; D. Septum;

144. Which of the following functions is impaired when the frontal lobes are damaged?

A. Long-term memory; B. Forecasting the results of actions; B. Attention; D. Recognition of human faces; D. Understanding the meaning of words.

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

1.2 Block of modulation, activation of the nervous system

1.3 Block of programming, launching and monitoring of behavioral acts

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

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 structural organization 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 lower limbs, middle areas - in the upper limbs of the contralateral side, and irritation of the points of the lower belt 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.