Behavioral, neurological, and biochemical studies are shedding light on the processes that produce sex differences in brain organization. Sex hormones begin to affect the brain at such an early age that the response to the external environment of differently wired brains in boys and girls differs significantly almost immediately after birth. The effect of gender on intellectual function appears more in the nature of mental abilities, and not in the general level of intelligence, measured by IQ.
Men are better oriented along the way, following a route. They need less time to remember the route, they make fewer mistakes. But after the route is memorized, women remember more landmarks than men. Apparently, they tend to use more visual landmarks in everyday life.
Men tend to be better than women at solving spatial problems. They perform better on tests that require you to mentally rotate an object or manipulate it in some way. They outperform women in tests that require mathematical reasoning (Kimura D., 1992). Men show great abilities for the formation of precise motor skills of aiming, throwing, and intercepting various projectiles.
Women, as a rule, surpass men in the speed of identifying similar objects, in arithmetic counting, they have better developed speech skills. Women cope faster with some manual tasks, where precision and jewelry of movements are required.
Since the genetic material in males and females is the same except for the sex chromosomes, rather, the different quality of mental abilities in males and females reflects the difference in hormonal influences on the developing brain. The separation of the sexes occurs in the early stages of embryonic development under the influence of estrogens (female sex hormones) and androgens (male sex hormones, the main of which is testosterone).
Testosterone causes masculinization, promotes the formation of male genital organs, and also forms stereotypes of male behavior already in the early stages of life. Sex hormones change the functioning of the brain only during a critical period of human development. The introduction of the same hormones in later periods of life does not cause such effects. The deprivation of newborn males of testosterone by castration or the introduction of androgens into newborn females leads in adulthood to a complete change in the forms of behavior specific to a given sex to the opposite. Female rats injected with androgens behave like males. They become more aggressive, prone to games with elements of a fight, and prefer good physical contact. Castrated males behave like females. At the same time, they show a tendency characteristic of females to use visual landmarks when performing tasks related to spatial learning.
A study of the behavioral characteristics and abilities of girls who, in prenatal or neonatal life, were exposed to excessive exposure to androgen (male sex hormone) due to congenital adrenal hyperplasia of their mothers, showed that, as they grew older, they showed more pronounced boyish behavior and greater aggressiveness. The effect was irreversible and was not corrected by drug therapy. They, like men, have better developed spatial functions. They better perform tests for spatial manipulation, rotation of objects. However, no differences were found in other perceptual or verbal tests requiring logical reasoning between the two groups of girls — with and without hormonal disorders -.
Many scientists believe that the difference between the male and female mind is based on the less pronounced asymmetry of the hemispheres in women compared to men. In women, damage to one cerebral hemisphere more often than in men causes a smaller defect, the same injury in men is accompanied by more pronounced consequences. There is evidence that the back of the corpus callosum is larger in women. This should indicate a more complete interaction of the hemispheres in women compared to men.
It has been established that in male rats the cortex of the right hemisphere is thicker than the left. This is consistent with other evidence that early exposure to the male sex hormone (androgen) leads to suppression of left cortical growth.
Observation of human embryos also showed that in future boys, the cortex of the right hemisphere is thicker than the left. However, as follows from the results of examination of men and women with damaged right hemisphere, the ability to rotate objects in space, which is better expressed in men, is not due to sexual functional differences in the right hemisphere. Damage to the right hemisphere did not cause more pronounced violations of spatial rotation in men than in women, as might be expected if such abilities in men were determined by the greater development of the right hemisphere.
A similar assumption about a more pronounced asymmetry of the brain in men was also expressed in relation to speech. This proceeded from the fact that aphasia is more common in men after trauma to the left hemisphere. On this basis, it was concluded that in women, both hemispheres are more involved in the organization of speech. However, the data obtained by some authors refute this opinion: among women with damage to the right hemisphere, aphasia occurs as often as among men with a similar injury.
D. Kimura (1992), studying speech disorders in men and women as a result of brain damage, found that in women the organization of speech and the motor functions associated with it are localized in the left frontal cortex.
In men, a center with similar functions is located in the posterior sections of the same hemisphere. After damage to the frontal part of the brain, women develop aphasia more often than men. With damage to the posterior parts of the brain (usually this injury occurs more often than lesions in the anterior parts), the speech functions of women suffer less often, not because they have less pronounced asymmetry of the brain, but because they are less likely to destroy the center of organization of speech movements, localized in the anterior regions of the brain. In men, the system for choosing and programming speech movements is located in the posterior parts of the hemisphere.
According to D. Kimur, the specificity of the left hemisphere is not only the programming and choice of speech reactions, but also the organization of complex movements of the mouth, hands involved in human communication. These functions in women are presented in the anterior regions, and in men — in the posterior regions of the hemisphere.
In women, the praxis system, which selects the appropriate hand movements, is in topographic proximity to the motor cortex immediately behind it, which may explain the ability of women to form finer motor skills. On the contrary, in men, movements such as aiming are better formed, i.e. directed at objects at some distance. These skills require close interaction with the visual system, located in the back of the hemispheres.
According to D. Kimura, the anterior motor control system of women is detected even in tests that require the simultaneous participation of visual information (construction of a figure from cubes based on a visual model). In women, when performing this test, large violations are found when the anterior rather than the posterior sections of the hemispheres are damaged. In men, there is an inverse relationship.
Although the functional asymmetry of the brain does not seem to affect the organization of speech and movements, as well as the ability to spatial rotation, however, it seems that the performance of some abstract verbal tasks depends on it. The performance of the test to assess vocabulary in women was affected by damage to both hemispheres, and in men only to the left. In other words, women use both hemispheres to a greater extent than men when comprehending words. At the same time, the motor skills of men are less dependent on the left hemisphere, since left-handers are more common among them. Among right-handed women, women are more right-handed than men: they prefer to use their right hand more often than men.
Thus, the asymmetry of the brain associated with sex differences, depending on the function, can be expressed in the dominance of different hemispheres. Therefore, one gender is not always more “asymmetric”. Thus, in women, the successful completion of verbal tasks is associated with the activity of the dominant left hemisphere. The same can be said about the greater percentage of right-handedness among them. In men, motor skills are less dependent on the left hemisphere.
As follows from the above data, the organization of the brain in men and women from a very early age follows a different path. This differentiation of development is directed by sex hormones, which forms different cognitive abilities in representatives of different sexes. Cognitive operations retain their sensitivity to sex hormones throughout life. Estrogen levels, which change during the menstrual cycle, affect cognitive processes. High levels of these hormones are associated with a relative deterioration in spatial abilities and an improvement in motor and articulation skills. In men, there are seasonal fluctuations in testosterone levels. At some optimal level in the blood, men show the maximum ability to solve spatial problems. The best results are noted in the spring, when testosterone levels are lower.