The Role of Biology
Decades of data from studies of different animal species show that hormones can play a role in determining the cognitive abilities that males and females develop. For example, during typical prenatal male development, high levels of hormones such as testosterone masculinize the developing brain and result in male-typical behaviors and probably male patterns of cognitive performance.
More recent studies have shown that hormones continue to play a role in cognitive development throughout life. Such changes have been observed in individuals receiving large quantities of male or female hormones in preparation for sex-change surgery. Researchers found, for example, that people undergoing female-to-male hormone treatment show “masculine” changes in their cognitive patterns: improvements in visuospatial processing and decrements in verbal skills.
The human brain is shaped by these hormones, as well as by our genetic inheritance and a lifetime of experiences, so it should not be surprising that numerous differences appear in female and male brains. In general, females have a higher percentage of gray matter brain tissue, areas with closely packed neurons and fast blood flow, whereas males have a higher volume of connecting white matter tissue, nerve fibers that are insulated by a white fatty protein called myelin. Furthermore, men tend to have a higher percentage of gray matter in the left hemisphere, whereas no such asymmetries are significant in females.
Imaging studies assessing brain function support the notion that females perform better on tasks such as language processing that call on more symmetric activation of brain hemispheres, whereas males excel in tasks requiring activation of the visual cortex. Even when men and women perform the same task equally well, studies suggest that they sometimes use different parts of their brain to accomplish it.
It is important to emphasize, though, that finding sex differences in brain structures and functions does not suggest these are the sole cause of observed cognitive differences between males and females. Because the brain reflects learning and other experiences, it is possible that sex differences in the brain are influenced by the differences in life experiences that are typical for women and men.