Although the biological basis of sex differences in the brain's structure and function has not been entirely elucidated, there are at least two reasons that the brains of men and women might be different, size and laterality of cognitive processes. These two reasons, however, are not entirely independent. As I mentioned earlier, men's brains are larger than women's brains and there are more neurons. Although these differences are at least in part developmental, it is unknown whether these differences between men's and women's brains are induced by differences in hormonal exposure during development, are related to genetic differences independent of the hormonal influence, or are a combination of both. Men's and women's brains from the fetus to old age are exposed to different sex hormones, and hormones might influence thought patterns, moods, and behavior, both during development and after maturation. As mentioned previously, one of the major differences between the brains of men and woman is the lateralization of cognitive functions, and it has been thought by several investigators that sex hormones might influence the laterality of functions (Geschwind & Galaburda, 1985; Witelson, 1991). Grimshaw, Bryden, and Finegan (1995) studied the relations between prenatal testosterone levels in second-trimester amniotic fluid and lateralization of speech, affect, and handedness at age 10. Girls with higher prenatal testosterone levels were more strongly right handed and had stronger left-hemisphere language-speech representations. Boys with higher prenatal testosterone levels had stronger right-hemisphere specialization for the recognition of emotion. This pattern of results is most consistent with the claim that prenatal testosterone leads to greater lateralization of function.
In addition, there is evidence that hormones such as androgens and estrogens might influence cognition, even postnatally. For example, Maki, Rich, and Rosenbaum (2002) studied 16 young women during two different stages of their menstrual cycle. During the follicular stage of the menstrual cycle, both estrogen and progesterone are low, and during the midluteal phase, both are high. These investigators found that whereas explicit memory was unchanged during the high estrogen phase, visuospatial functions were not as well-performed as during the low estrogen phase. Choi and Silverman (2002) studied the relationships between route-learning strategies and circulating testosterone and estrogen in a large population of students by obtaining salivary assays from the students. They found that testosterone levels were positively correlated with the use of route-learning strategies in men, but not in women. In addition, Wisniewski (1998) compared the spatial ability of hypogonadal men to normal men and found that the hypogonadal men had a decreased left-visual-field-right-hemisphere superiority, suggesting that testosterone might have a greater influence on the right hemisphere than left hemisphere, and the right hemisphere appears to be dominant for performing spatial tasks. Keenan, Ezzat, Ginsburg, and Moore (2001) studied frontal-lobe executive functions in postmenopausal women while they were taking or not taking estrogen and found that executive functions improved with estrogen. Although divergent thinking, so important in creativity, is, at least in part, mediated by the frontal lobes, I could not find any studies that examined women's creativity while they were on and off estrogen.
On the basis of some of the studies I reviewed earlier, Kimura (2002) concluded that gender differences in the cognitive abilities are a product of not only current but also early hormonal environments. Thus, it is possible that men have a better chance of being recognized as creative because they have better spatial abilities and that this difference might reflect genetic and hormonal influences both early and late. Independent of spatial abilities, however, we still do not know if a person's gender influences creativity.
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