Each person has their own unique palette of feelings and emotions. This determines his individuality and sets him apart from other individuals. From a scientific point of view, asymmetry, which characterizes the distribution of mental acts of activity in the hemispheres, is responsible for such mental originality.

The first assumptions about the different functions of the left and right hemispheres of the brain belong to the twentieth century. Scientists began to conduct experimental experiments on human brain in order to determine the functional affiliation of each hemisphere.

Functional asymmetry of the hemispheres, according to most scientists, is an evolutionary breakthrough that indicates a high level of development of the human mind. Functional asymmetry is based on genetic roots, that is, it is prone to hereditary transmission to descendants.

It is formed in close relationship with society, during the social formation of the individual. The dominant hemisphere is considered to be the one whose side is responsible for speech function. According to this theory, the overwhelming number of people have a dominant in the form of the left hemisphere - they are right-handed. Left-handers, accordingly, have the opposite picture, which is reflected in their thinking strategy.

Depending on the dominant hemisphere, all people can be divided into three large categories:

• Left hemisphere about 40 - 42% of the total population
• Right hemisphere from 10 to 20%
• Equihemispheric, having equal development of both hemispheres, about 40%

Right-hemisphere people, also known as left-handers, have always aroused public interest due to their uniqueness. Some peoples preferred to beware of left-handers, putting a negative meaning into this word. In fact, there is no pathology in being left-handed. This does not cause psychological abnormalities, but is individual feature personality.

According to statistics, left-handers more often become writers, journalists, artists, organizers, and left-hemisphere people, otherwise right-handers, become engineers, mathematicians, philosophers, and linguists.

The easiest way to assess the characteristics of brain asymmetry is to compare the development of the right and left hands. People who predominantly use their right hand when writing are right-handed and, accordingly, belong to the left-hemisphere type. Lefties are exactly the opposite. In addition, there are a number of tests that help determine belonging to the type of dominant hemisphere.

One such method is the “Napoleon Pose” or the arm crossing test. People who, when crossing their arms, right hand turns out to be on top of the left forearm are defined as right-handed, that is, left-hemisphere, otherwise - left-handed, that is, right-hemisphere.

Distribution of functions in the cerebral hemispheres

Each of the hemispheres of the brain has its own direction of functioning, creating, when acting together, a unique and inimitable combination of personality. The predominance of one hemisphere in the functioning of the brain leads to increased personal qualities in one direction or another. Right-hemisphere people are characterized by contemplation, subtle sensitivity and a desire to delve into the jungle of memories.

A person with a predominance of the right hemisphere is often slow and taciturn. And left-hemisphere people show a tendency towards analytical thinking and “iron logic”, they are easily given theoretical knowledge, they have considerable vocabulary, one can often say about such people “they won’t put their words in their pocket.” They are active and purposeful.

The main features that belong to each hemisphere are:

Both hemispheres are connected in their action, providing the personality with a holistic set of qualities, but each of them brings its own bit of uniqueness.

At the beginning of development, in the first years of life, right hemisphere big brain dominates over the left in functional terms, and the left catches up with it in the second year of life; over time, the hemispheres alternately overtake each other in development. The right and left hemispheres are united by the corpus callosum, which serves as a bridge between them and reaches its final development at the age of 25; in women it is usually larger.

The concept of symmetry in the human body as such is absent. The asymmetry of the hemispheres is closely related to the symmetry of the human face. People's faces are not symmetrical, this is a normal physiological condition. There is a relationship between hemisphere and facial asymmetry.

In left-hemisphere people or right-handed people, the nose is most often deviated right side, and for right-hemisphere or left-handed people - to the left side of the face. Raising one eyebrow often belongs to the narrow half of the face, and a crooked smile belongs to the wider half.

Thanks to the asymmetry of the brain, the coordinated work of brain structures is carried out by distributing the functional load between the two hemispheres, combining information and controlling each of the hemispheres over its inherent processes. Due to the fact that each of the brain functions is distributed in relation to both hemispheres, clinical damage to the right or left hemisphere will vary.

This allows us to identify functional asymmetry of the brain as a diagnostic basis for identifying many neurological diseases. Only the unity of the work of both hemispheres, their asymmetrical function, makes it possible to guarantee perfect human life.

IN recent years the development of higher mental functions of a person is associated with the level of interhemispheric asymmetry (lateralization) of the brain. According to psychologists, brain lateralization is one of the conditions for normal development, for example, the ability to read or develop articulate speech.

The absence of lateralization is observed in cases of various anomalies in mental development, in particular in schizophrenia, Down's disease, etc.

The most obvious external manifestation of interhemispheric asymmetry is the dominance of a certain hand in the implementation of motor acts - the so-called “right-handedness” and “left-handedness”. However, asymmetry is also manifested in the dominance of not only the hands (“leading hand”), but also the legs, eyes, and ears (respectively, “leading”)*

It has been experimentally shown that in right-handed people the dominant left hemisphere, and many “lefties” have the right one.

Research has shown that these external manifestations of asymmetry often reflect deep natural features of the mechanisms of the human psyche and behavior. They include the specifics of inclinations, temperament, motor activity, extra-introversion, emotionality, methods of self-expression, etc. In this regard, left-handed people are of particular interest.

About left-sided asymmetry

Lefties make up a significant percentage of the population in many countries. According to 1988 data, 25 million Americans are left-handed. In Brazil they make up 10% of the total population. There is now a trend towards an increase in the number of left-handers in the human population. In this regard, initiatives are increasingly emerging to create a subculture for left-handed people, which would make their life easier in the “right-wing” world.

As an analysis of specialized literature shows, there are three points of view when assessing the psychophysical characteristics of left-handed and right-handed individuals. According to one of them, left-handers have lower rates of mental development. The word "right" has an Anglo-Saxon source, meaning "correct", "honest", - "straight"; the word “left” means evil, “dishonest”, “deceitful”.

Marked negative qualities Left-handers: lower level of intelligence, lack of confidence, less ability to learn, greater propensity for drugs and crime.

According to the second point of view, left-handers do not differ from right-handers in the main indicators of higher mental functions. Studies conducted on large samples have shown the absence of any significant differences in academic performance between left-handed and right-handed schoolchildren. However, the arguments are questioned on the grounds that they were conducted under normal conditions, and the specificity of left-handers, according to other sources, manifests itself mainly in unusual situations, for example, in stressful ones.

There is a third point of view: left-handers have higher rates of mental development than right-handers. For example, in Japan, left-handers are especially respected as more skilled craftsmen. Everyone knows the left-hander from story of the same name Leskova, “shoed the flea.” Left-handers are better at solving numerical problems; their special achievements in sports are known: they are the best boxers, fencers, etc. The third point of view is supported by the fact that many talented and brilliant people were left-handed: Michelangelo, Leonardo da Vinci, Joan of Arc, Charlie Chaplin, Maxwell, K . Bakh, I.P. Pavlov, Lewis Carroll and many other outstanding personalities.

What are the characteristics of the mental properties of left-handers? What are the structural features of their brain? How did these features develop during evolution and how do they develop during ontogeny in humans? What is the role of heredity and environment in the formation of interhemispheric asymmetry? These issues will be discussed in subsequent sections.

About the structure of the brain of “right-handers” and “left-handers”

The discovery of morphofunctional asymmetry of the brain itself was made in the clinic. In 1960, the French neurologist P. Broca found that with hemorrhages in the area of ​​the inferior frontal gyrus, and in most patients - in the left hemisphere, the patient loses the ability to pronounce words. This is how the speech motor center (Broca's center) was discovered. Then Wernicke discovered the speech-hearing center in the superior temporal gyrus. Then the speech-visual center and the center were opened writing. Studies have shown that there is a fairly clear correlation between right-handedness and the localization of the speech motor center in the left hemisphere.

The problem of “right-handedness” - “left-handedness” has long been studied by psychologists, but morphological studies aimed at exploring the structural and functional foundations of this phenomenon have practically begun only in recent years. This is explained by many reasons, in particular, the extremely high individual variability of the brain structure and the great methodological difficulties of studying interhemispheric asymmetry. Studying on sectional material is associated with limited information (or lack thereof) about the “leading” hand. Intravital studies require very complex and expensive equipment, and, in addition, the possibility of obtaining sufficiently representative samples is very limited.

Significant difficulties are also associated with establishing the morphofunctional correlations themselves in such areas as the human psyche.

Nevertheless, there is information in the literature about some features of the structure of the brain in left-handers and right-handers. Thus, it has been shown that in 70% of cases the length of the so-called planum temporale (part of Wernicke's area) is greater in the left hemisphere than in the right. This matches percentage"right-handed" in a random sample of people. It is known that the asymmetry of the dimensions of the temporal plane increases with age.

Studying asymmetry in a living person using angiography and computed axial tomography is of significant value. They make it possible to directly compare morphological asymmetry with functional asymmetry (for example, with data on the predominance of activity in one of the hands). These studies showed that the brains of right-handed people have greater anatomical asymmetry than left-handed people. Angiographic studies (the study of blood vessels) show that in most cases the middle cerebral artery, which runs along the Sylvian fissure, has a steeper rise in the right hemisphere and rises higher than in the left. The computer axial tomography method allows you to study brain structures in any section. Using this method, it was found that in “right-handers” the parietal and occipital lobes in the left hemisphere are wider than in “left-handers”. Their frontal lobe is wider in the right hemisphere. The depth of impressions on the inner surface skulls (endocranes).

According to the work of the Brain Institute, in individuals with musical and artistic abilities, the left hemisphere dominates in terms of pronounced apicalization (multiple branching of apical, i.e., apical dendrites) neurons of layer III, horizontal striation of layers IV and V, radiarity of layers VI and VII. The right hemisphere dominates in the number of ultra-small neurons in field 17. In 70-80% of the examined visual field 17 in the right hemisphere was dominant in the width of layers III and V.

Our data on the study of the vascular bed of specifically human cortical areas showed that in speech areas in 75% of cases the left hemisphere dominates in terms of volumetric vascular density.

By comprehensive characterization structural and quantitative characteristics of the hemisphere, including the inferior frontal gyrus, three variants of features and structure can be distinguished, quite clearly different from each other.

The majority (70-80%) of the studied brain specimens are characterized by: 1) left-sided dominance along the arc length of the hemisphere; 2) triangular gyrus of the most complex type with a left-sided dominant complexity; moreover, its apex rests directly on the Sylvian fissure, in which the middle cerebral artery is located; 3) the ascending and horizontal branches of the Sylvian fissure extend directly from it almost at right angles to each other; 4) interhemispheric asymmetry in the pattern of the sulci is clearly expressed.

The second group (6-8%) is characterized by: 1) right-sided dominance along the arc length of the hemisphere; 2) the triangular gyrus has an insufficiently complex structure (2nd or 3rd type of complexity), its apex does not reach the Sylvian fissure; 3) the ascending and horizontal branches form acute angle and depart from a common stem extending from the Sylvian fissure; 4) interhemispheric asymmetry in the pattern of sulci is not pronounced.

The third group (22% of specimens) combines the characteristics of the first two.

Since the identified groups in their numerical ratio correspond to the data on the quantitative proportions of left-handed and right-handed people in a random sample of people, and also based on the fact that many of the studied criteria have a pronounced functional significance, we can compare these groups with phenotypes: the first group is “right-handed” ", the second - "left-handed", the third - ambidextrous (equal use of both hands).

The state of interhemispheric asymmetry in the process of ontogenesis

Signs of morphological asymmetry of the brain in the speech motor cortex appear very early. Differences between the right and left hemispheres are noticeable already in a 5-month-old fetus. Thus, according to our data, in the region of the inferior frontal gyrus, in most of the cases studied, the ascending branch of the Sylvian fissure first appears in the right hemisphere. During embryonic development, the right hemisphere is slightly ahead of the left. Thus, the insula in the right hemisphere is more often immersed in to a greater extent than in the left. The arc lengths of the hemisphere as a whole and the frontal lobe in the right hemisphere are greater than in the left, etc.

Starting from 7 months of the fetal period and up to 2 years of life, according to many indicators, the right hemisphere turns out to be more “advanced” compared to the left. The age of 2-5 years is a turning point, and the left hemisphere becomes dominant.

A similar direction of asymmetry was also noted by employees of the Brain Institute of the Russian Academy of Medical Sciences (works by I.N. Bogolepova and co-workers) in relation to the structural-quantitative relationships of the cytoarchitectonics of fields 44 and 45. It was shown that in terms of the volume of structures, neuron density, width of the cortex, glioperineuronal index, etc. A newborn child has a right-sided asymmetry. Subsequently, the sign of the asymmetry changes, and the value of many indicators becomes greater in the left hemisphere.

The data presented correspond to the observations of psychologists about the early manifestation of functional asymmetry of the brain. It increases during human ontogenesis and decreases in old age.

One of the psychological hypotheses considers the brain of a child under two years of age to be functionally split due to the immaturity of the corpus callosum. When manipulating objects in such a child, the formation of engrams occurs in each of the hemispheres, independently. Subsequently, due to the predominant use of the right hand, the dominant role passes to the left hemisphere.

After two years, the corpus callosum begins to function, and the dominance of the left hemisphere increases. The function of spatial analysis, which was initially localized bilaterally, is displaced to the right hemisphere. Until about four years of age, the right hemisphere “speaks language” as successfully as the left. It is possible that the separation of the hemispheres is very early age would lead to the fact that each hemisphere, separately and independently of the other, would be able to carry out high-order mental functions, similar to those that usually only the left hemisphere possesses in humans.

Our sequential study the structure of the inferior frontal gyrus in different age periods of pre- and postnatal ontogenesis showed that the development of the left hemisphere, at least in the early stages, proceeds according to an independent program, in comparison with the right hemisphere. Thus, starting from the prenatal period, elements of the “structural features of the future” of the left hemisphere complex of “right-handers” appear in the left hemisphere: a clearly represented inferior frontal sulcus, separating the inferior frontal gyrus from the middle one: the ascending and horizontal branches of the Sylvian sulcus, first extending from the common trunk and dividing the inferior frontal gyrus into triangular, opercular and orbital. IN further development This complex goes in the direction of outstripping the growth rate of the triangular gyrus, which, as it were, “pushes apart” the opercular and orbital gyri, growing between them. Opercularization of the insula in this case occurs mainly due to the triangular gyrus. This gyrus itself takes the shape of an inverted dome with a blunt apex. The ascending and horizontal branches of the Sylvian fissure cover this dome from below, forming a kind of “bowl”.

The described complex is expressed in the inferior frontal gyrus of the left hemisphere in the majority (67-70%) of the studied specimens of the adult brain (right-handed individuals). These data show that, along with the signs noted in the literature (dominance in the left hemisphere of the planum temporale, structural features of the Sylvian fissure), “right-handers” also develop a whole complex of structural and quantitative features in the left inferior frontal gyrus. Its elements are noticeable already in the prenatal period. In single instances it manifests itself at very early stages of postnatal development (in a 4-month-old child), but is fully detected from 2 years of age.

The early appearance of signs of the “left hemisphere” complex in brain ontogenesis indicates a significant role of the genetic factor in the development of right-hand dominance (right-handedness). At the same time, its most intensive formation, accompanied by the subsidence of the island as a result of the “influx” of triangular, opercular and orbital convolutions onto it, takes a period of 2 to 6 years. The final formation with a clear dominance of the triangular gyrus, often acquiring a dome-shaped shape, with the development of the superficial component of the gyri and the emergence of a large-gyral formation occurs in the period from 6 to 10 years.

The presented morphological data correspond to the concept of the role of genetic and environmental factors in the dominance of the right hand (and therefore the left hemisphere), which is discussed below.

On the role of heredity and environment in the formation of interhemispheric brain asymmetry

Three main factors play a role in the formation of morphofunctional interhemispheric asymmetry of the brain: heredity, environment (here, the educational system) and pathology. There is a connection with ecology. Thus, among the population of the North - Eskimos, Chukchi, Koryaks, etc. - the right-hemisphere phenotype is more common (left-handed people are more common). This is probably due to their maximum adaptability to living conditions. Pressure cultural traditions, aimed at predominant use of the right hand, is weaker in them than in middle lane Russia. Perhaps this is due to their less familiarity with scientific and technological progress and their greater proximity to nature.

A parallel has been noticed between the degree of pressure from the social environment towards right-hand dominance and the percentage of left-handed people in the population. Thus, in China the percentage of left-handers is relatively small (3.5%). Environmental pressure is comparatively stronger in the US, left-handed people make up 11.5%. The pressure of the environment is weakened.

Of the many genetic hypotheses about the inheritance of left-handedness and right-handedness, the most interesting is Annette's hypothesis. Most people have the gene for right-handedness (“right-sided shift factor” - rs+). If a person has this gene, then he is predisposed to become right-handed with left-hemisphere localization of speech. In the absence of it and the presence of the recessive allele rs, a person can become either right-handed or left-handed, depending on the circumstances, for example, depending on the conditions of embryonic development.

In the human population, there is probably a balanced polymorphism associated with the distribution of the dominant right-shift gene and its recessive allele. The influence of the gene affects not only the preference for one of the hands, but also other types of asymmetries (leg, ear, eye), however, the most objective external assessment of lateralization is the assessment of the leading hand.

The “right shift” gene leads to the development of asymmetry. In early ontogenesis, on the one hand, it inhibits the development of the plenum temporale in the right hemisphere, and on the other hand, the development of the left posterior parietal region. Due to this, the left temporal region receives advantages in phonetic processing processes, and the right posterior parietal region receives advantages in spatial vision processes. Homozygotes for the rs+ gene are distinguished by a particularly strong “right shift”. They will have a pronounced dominance of the right hand and weakened activity of the left, and the function of the right hemisphere in relation to the assessment of spatial relationships will be somewhat inhibited. In general, the rs+ gene has a negative effect on spatial judgment abilities.

Homozygotes for the recessive rs- gene, on the contrary, are distinguished by inhibition of the speech center of the left hemisphere and form a risk group in terms of speech development, especially the phonological aspect.

Heterozygotes for the rs+ gene have the greatest advantages, since they do not have such severe weakness of the left hand and right-hemisphere spatial abilities.

IN psychological literature the “ontogenetic hypothesis of interhemispheric brain asymmetry” was formulated. The origin of asymmetry is determined by five main factors.

1. A lateralizing factor of a non-genetic nature (most likely a weak type of physical influence), under the influence of which the left half of the body, and therefore the left hemisphere of the brain, has some advantages in the speed of embryonic development. Power of action this factor not very big.

2. Genetic mechanisms that form a bilateral trait. Manifestations (non-manifestations) of genetic dispersion of asymmetry depend on the characteristics of the phenogenesis of each trait.

3. Penetal environmental influences (stress, stroke, etc.), causing the emergence of an atypical (pathological) interhemispheric organization, in particular, left-handedness.

4. Environmental, systematic (cultural) influences that contribute to the formation of cerebral organization and functional specialization of the cerebral hemispheres. This factor significantly increases the incidence of right-handedness.

5. Environmental stochastic influences, which increase with age and with age-related cerebral pathology and are manifested by a violation of interhemispheric relations. The direction of the asymmetry does not change significantly, but becomes difficult to determine; the absolute value of asymmetry increases.

Psychological testing based on functional brain asymmetry

The concept of an individual asymmetry profile is being developed in the psychological literature. The latter includes the analysis of not just one sign (perhaps the most obvious, but not exhaustive, for example, manual asymmetry), but a whole complex - various criteria for motor and sensory asymmetry (leading hand, leading leg, leading eye, leading ear). In the works of T.A. Dobrokhotova and N.N. Bragina provides methods for determining these criteria. They are decisive in establishing the individual asymmetry profile.

Knowing the features of functional asymmetry in humans, it is possible to identify the hidden, most various shades human character. This assessment can be made using four main tests:

1) interlacing fingers;

2) determining the dominant eye in aiming ability;

3) Napoleon's poses;

4) applause.

Based on various combinations signs of asymmetry, 16 mini-portraits of brief generalized psychological characteristics which are given below. Designations: the first two letters are hand and foot, respectively, the third letter is eye, the fourth is ear.

1. PPPP (“completely right-handed”): only right-wing asymmetries: conservatism, orientation towards generally accepted opinion (stereotype); Such people do not like to conflict, argue, or quarrel.

2. PPPL: the most striking character trait is indecision.

3. PPLP: coquetry, determination, sense of humor, artistry, very contact type of character, more often found in women.

4. PPLL: rare combination; the character is close to the previous one, but softer; there is some contradiction between indecision (left applause) and strength of character; leading eye right.

5. PLPP: analytical mind and gentleness; more common in women; slow addiction, caution in relationships, tolerance and some coldness.

6. PLPL: the rarest combination; defenselessness, exposure different influence; more common in women.

7. DILI: very common combination; emotionality; lack of persistence on major issues; amenable male influence, which allows you to adapt to different conditions; happy with friends and easy to get along with people.

8. LPPL: greater than previous types, gentleness of character, naivety.

9. LLPP: friendliness and simplicity; some scattered interests and a tendency to introspection.

10. LLPL: innocence, gentleness, gullibility.

11. LLLP: emotionality, energy and determination.

12. LLLL (“full left-handed”): anti-conservative character type; the ability to look at old things in a new way; the greatest emotionality, individuality, selfishness, stubbornness, sometimes turning into isolation.

13. LPLP: the most strong type character; find it difficult to change their point of view; energetic and persistent in achieving their goals.

14. LPLL: similarity to the character of the previous ones, instability, tendency to introspection; have difficulty finding new friends.

15. PLLP: easy character; know how to avoid conflicts and easily find friends; Hobbies change often.

16. PLLL: impermanence and independence; the desire to do everything yourself.

You can tell about a person’s character traits by performing even one test. If the left finger rests on top of the intertwining of fingers, this indicates emotionality, if the right one speaks of an analytical mindset. The right dominant eye speaks of a firm, persistent, more aggressive character, the left - of a soft and compliant character. If in Napoleon's pose you are on top left hand, then the person is capable of coquetry, if the right one is capable of simplicity and innocence.

On the social and genetic significance in the formation of an individual asymmetry profile

Studies of some physiological characteristics, as well as some properties of higher nervous activity conducted at the Department of Anatomy, Physiology and Valeology of Moscow State Pedagogical University showed that the individual profile of asymmetry in schoolchildren of all age groups and students is formed in the process of postnatal ontogenesis. In a group

of right-handers, complete right-handers account for 22.2%, dominant right-handers - 50%, right-handers with the presence of left-sided dominants - 8%, right-handers in the motor system and left-handers in the sensory system - 8%, and partial ambidextrous - 12%.

In the left-handed group, complete left-handers account for 6%, dominant ones - 27%, left-handers with right-sided dominants - 40%, left-handedness in the motor system and right-handedness in the sensory system - 12%, partial ambidextrous - 12%. In general, among older schoolchildren, compared to younger ones, the number of complete right-handers, as well as those with right-sided dominance, increases. So, if at the age of 8-10 years complete right-handers make up 4%, and dominant ones - 12.5%, then from 11 to 18 years old they make up 11% of all subjects, and dominant ones - 33.3%.

In children with more high level the predominance of the right hand has a higher indicator of motor plasticity, i.e. speed of movements, flexibility when switching from one form of motor activity to another. Right-handers are also distinguished by higher rates of processing speed of visual information, a higher value general activity in motor and communication areas. Left-handers have higher levels of concentration and volume of visual information, higher values ​​of general emotionality with a predominance of negative emotions.

In older schoolchildren, compared to younger ones, the number of combinations of the right leading hand with the right leading eye increases (for schoolchildren aged 8-10 years it is 11%, for schoolchildren older than 11-31%). The predominance of right-sided dominance in older age is expressed in both the motor and sensory systems (hand-foot, hand-ear, foot-ear, foot-eye), however, it is most expressed in the hand-eye system. This indicates the special social significance of this system and the importance of the conditions of the social environment in its development.

At the same time, some factors indicate a fairly early formation of the morphofunctional hand-eye system in human embryos. Unlike animals, this is manifested in a special position of the anlage of the future hand - clearly opposite the anlage of the optic cup (Fig. VIII. 1).

From this we can conclude about significant influence and genetic factors on the development of the hand-eye system. Thus, the idea of ​​special ontophylogenetic relationships of a person in connection with his biosocial essence is confirmed. Apparently, some higher mental properties (the ability to improve, the desire to join social progress, etc.) can be transmitted not only according to the laws of social heredity, but also through the genetic program.

The individual asymmetry profile is formed, to a large extent, in the process of individual development, based on brain plasticity. Genetically programmed right-sided dominance is realized under the influence of social factors- training, traditions, upbringing, acting in the direction of the predominant use of the right hand. Strengthening the right-sided dominants indicates a special plasticity of the left hemisphere. It is no coincidence that in its immediate vicinity there are centers of hand movement, as well as speech and oculomotor centers. Numerous variants of the individual asymmetry profile reflect the functional diversity of mental properties of human populations.

Formation of morphofunctional asymmetry of the brain in anthropogenesis

Based on the analysis of ancient Paleolithic images, we can confidently assume that Paleolithic man was most likely ambidextrous; It is also possible that in those days the percentage of left-handed people was higher than that of right-handed people. Among our contemporaries, a high percentage of left-handed people was found among the Australian aborigines, as well as among the Eskimo hunters.

There is a fairly clear connection between speech and motor asymmetry (lateralization). The left hemisphere is dominant in relation to speech in right-handed people. Some researchers express the opinion that the center of movement of the tongue turned out to be predominantly in the left hemisphere, not because it gradually, in the process of evolution, became more and more connected with symbolism, but because the motor center of speech turned out to be connected with the center of hand movement localized nearby and fingers of the hand. It is believed that the predominantly left-hemispheric localization of the speech center arose in the process of evolution, due to a change in the control centers of the communication system. On initial stages During the process of hominization, the system of communication was gestural. At this stage, in the area of ​​the middle frontal gyrus (mainly the left hemisphere) there was a control center for the movements of the right hand. Hand indicated various directions movement, management of a team of people was carried out during relocation, during labor operations, etc.

Subsequently, the vocal muscles and tongue muscles began to be used for communication. And since the area of ​​control of these muscles is located in the brain adjacent to the centers of the hand (also predominantly in the left hemisphere), it was the left hemisphere that became dominant in the control of speech, both oral and written.

Security questions

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Medical psychology. Full course Polin A.V.

Interhemispheric asymmetry

Interhemispheric asymmetry

Sensory asymmetries

Vision. In the visual analyzer, asymmetry is observed on average in 90% of cases. The majority of subjects (60%) show a predominance of the right eye, which is called the leading eye. Color is perceived immediately by the dominant eye, and a little later by the non-dominant eye. The right eye has a wider field of view and is better at aiming. Some painting effects are designed to address the phenomenon of vision asymmetry.

Hearing. The phenomenon of sensory asymmetry concerns hearing acuity and the ability to more accurately locate the source of a sound. Thus, most healthy people hear better with the left ear, and the right ear copes better with the task of identifying the location of the sound source. This phenomenon is called the right ear effect. Differences in perception between the right and left ears appear at the age of 4 years; in girls this phenomenon appears earlier than in boys. The greatest intensity of this phenomenon persists between 5 and 12 years.

Touch. In the process of touch, about 80% of subjects believe that for the left hand this process is somewhat more complicated than for the right. If we consider the adequacy of assessing the subject-spatial properties of the objects under study, then the right hand is characterized by greater success, and if we are talking about the most complete assessment possible in a short period of time with one hand, then the left hand is more successful. If we consider each sensitivity option separately, it turns out that pain, vibration and temperature sensitivity are higher on the left hand, and kinesthetic sensitivity is higher on the right. The distribution of sensitivity in children deaf from birth, in contrast to hearing ones, is interesting. Deaf children aged 10–11 years right hand They recognize figures better, and letters with the left, while hearing people recognize the opposite.

Smell. 70% of adults note that left side the nose is more sensitive to odors, and in children no difference between the halves can be detected.

Taste. The vast majority of people notice that taste sensations are sharper on the left side of the tongue.

Any type of activity is accompanied by interhemispheric asymmetry. Electroencephalographic studies indicate that during intellectual activity there is significantly greater activity in the left hemisphere. Processing of received information is carried out differently by different hemispheres.

When studying the activity of the visual analyzer, it was found that the right hemisphere first describes the details of the image, after which they are generalized. In the left hemisphere, the process has the opposite direction - from the general to the particular. The result of such features is the fact that when comparing two objects or images, elements of similarity are more quickly established by the left hemisphere, and elements of difference by the right. Indicative are the experiments conducted in a psychiatric clinic on patients who received treatment leading to inhibition of the functions of one of the hemispheres and activation of the functions of the other. The right hemisphere, acting in isolation, perceives metaphors and idioms much better than the left, but also better than both hemispheres acting together. As it turned out, the right hemisphere better retains individual pieces of text - phraseological units, curses, which can be considered as cliches. Idioms are the same cliches that cannot be deciphered, but which can be remembered and known.

The right hemisphere is better suited for recognizing the spatial characteristics of visual and auditory stimuli, as well as verbal stimuli characterized by high specificity. As a working hypothesis, neuropsychology uses the statement that the right hemisphere lives and acts in the present time based on the past, and the left hemisphere lives and acts in the present based on the future time. Hemispheric asymmetry is also characterized by a difference in emotional response. For positive emotions The left hemisphere is responsible, and the right hemisphere is responsible for negative ones. Various experimental data indicate that both hemispheres take part in solving any problem. This does not depend on the way information is processed and the way the problem is solved.

It is characteristic that it is the type of the proposed task that is the main factor activating specific brain structures of one of the hemispheres. The type of task can include detection, recognition, identification, comparison and other processes. For better understanding The question uses the concepts of “individual lateral profile of a person” or “profile-lateral organization”, which consider several specific leading systems (for example, visual and auditory analyzers) as an indicator of asymmetry.

Lateral functional differences in brain pathology

With focal unilateral brain lesions on the right or left, two most significant clinical facts are distinguished.

1. There is a significant difference in mental disorders in right-handed people when the pathological process is localized in the right or left hemisphere. When the right hemisphere is damaged, disturbances occur in the psychosensory sphere, the processes of perception and sensory knowledge of the surrounding world and oneself in it are disrupted. When the pathological process is localized in the left hemisphere, a violation of motor behavior, speech function, as well as the processes of cognition and thinking associated with them occurs.

Less clearly visible differences are also noted. For example, depression occurs in both right- and left-hemisphere localization of the pathological process, but in right-hemisphere pathology, depression has a melancholy character and is accompanied by motor and general mental retardation; with left hemisphere pathology, depression is anxious, accompanied by motor restlessness. Auditory hallucinations when the lesion is localized in the right hemisphere are non-verbal in nature, the patient hears imaginary music or some other sounds, and when the lesion is localized in the left hemisphere, the hallucinations have the nature of imaginary speech statements.

2. The above-described patterns are not observed in left-handed people. In rare cases, the disorders detected in left-handers will be the same as in right-handers, but there have not been any left-handers in whom the pattern of the pathological process in its patterns would be opposite to that of right-handers. In most cases, pathological symptoms in left-handers depend less on which hemisphere is affected. The most clear dependence of the pathology emotional sphere from the affected hemisphere. With left-sided damage, attacks of despair, aggressiveness, intolerance and other phenomena of dysphoria are noted, and with right-hemisphere damage, euphoric reactions are characteristic.

According to the method of processing information in case of violations on the part of the left hemisphere, the following violations are observed in right-handers:

1) inability to isolate the most significant features from the information received and summarize them;

2) inability to identify significant features for choosing a method for classifying elements of received information and carrying out the classification process itself;

3) inability to learn and acquire any new experience;

4) inability to remember general categories.

With disorders of the right hemisphere, right-handers experience the following disorders:

1) inability to evaluate specific features something with preserved ability to generalize;

2) inability to remember the individual characteristics and characteristics of something or someone;

3) inability to evaluate the spatial properties of objects and features.

Emotional disturbances are more pronounced in pathology of the right hemisphere than in the left. With right-sided damage, lability of emotional reactions is observed, as well as an inability to self-control one’s emotional state. Such patients are distinguished by cheerfulness, complacency, as well as indifference to the environment and carelessness in everything, including regarding their own illness (anosognosia). With left-sided lesions, lethargy, lethargy, and negative emotional experiences in the form of anxious depression with bouts of anxiety and fear are noted. It is conventionally accepted that in right-handed people positive emotions are formed in the left hemisphere, and negative ones in the right.

The problem of left-handedness. “Left-handedness” is the predominance of the functional significance of the left-located paired organs over the right ones when performing functions together and is a feature of interhemispheric asymmetry. “Left-handedness” is not identical to the concept of left-handedness. It often happens that with normal mental development, most of the paired organs are “right-handed,” and one or two are “left-handed,” and vice versa. Complete right-handers occur in 38–54% of examinations, and complete left-handers occur in no more than 2% of cases. At the moment, there are three theories of the origin of “left-handedness”. According to the first of them, “left-handedness” is a hereditary characteristic and is determined by chromosomal characteristics. The second theory is called sociocultural and associates “left-handedness” with the constant preferential training and use of the left hand. The pathological theory explains the phenomenon of “left-handedness” as a result of traumatic brain injury, most often birth. In each specific situation, “left-handedness” is considered both the result of one of these reasons, and their combination.