Male brain and female brain.

Abstract

Men and women, so different in their adult behavior, are expected to have different brain organizations. Research with nonhuman animals has recently begun to uncover the brain mechanisms in the hypothalamus that underlie male-female differences in such basic functions as mating behaviors. Furthermore, even in the higher structures, sex differences have been observed.Sex differences in brain asymmetry have been reported for a species of albino rat. Diamond et al. (1981) reported that male rats showed significant thicker right hemispheres at all ages except very old. On the other hand, female rats somewhat showed thicker left hemispheres, although the differences for females were not significant statistically. Furthermore, measurements of the hippocampus show laterality effects as well. The male rat has large, significant differences favoring the right hippocampus early in life: these differences decrease considerably with age. The female rat shows the reverse asymmetry; the left hippocampus is thicker than the right, with the differences reaching statistical significance only at 21 and 90 days of age. In addition, the size of the corpus callosum is larger in the male rat than in the female rat. If testosterone is administered to newly born female rats, the corpus callosum becomes larger. On the other hand, male fetuses exposed to an antiandrogen have a smaller corpus callosum.Such facts emerging from the animal literature provide indirect support for the notion that the human brain is sexually differentiated. A quantitative analysis of the volume of 4 cell groups in the interstitial nuclei of the anterior hypothalamus (INAH) of 22 age-matched male and female individuals showed gender-related differences in the 2 cell gropus. One nucleus (INAH 3) is 2.8 times larger in the male brain than in the female brain irrespective of age. The other cell group (INAH 2) is twice as large in the male brain, but also appeared to be related in women to circulating steroid hormone levels. These results suggest that functional sex differences in the hypothalamus may be related to sex differences in neural structure (Allen et al., 1989). The volumes of four cell groups in the INAH 1, 2, 3 and 4 were measured in postmortem tissure from two subject groups: men who were presumed to be heterosexual, and homosexual. No differences were found between the groups in the volumes of INAH 1, 2 or 4. INAH 3 was more than twice as large in the heterosexual men as in the homosexual men (LeVay, 1991). This finding indicates that INAH is dimorphic with sexual orientation, at least in men, and suggests that sexual orientation has a biological substrate.Sexual differentiation is not limited to hypothalamic structures. Sylvian fissures of 67 brain specimens were measured postmortem from people who had been tested before death for detailed hand preference. Men having consistent-right-hand preference had longer the horizontal segments of sylvian fissure in both hemispheres compared to men not having consistentright-hand preference. Contrary to this, no...

The role of mindfulness in predicting individual performance.

“…Neuroscience research also provides reason to expect that the relationship between mindfulness and performance differs by gender. Studies show that males tend to rely on their left hemisphere when doing cognitive activity, whereas females tend to use both sides of their brain for the same task (e.g., Amen, 2004; Ashbrook, 1989; Baron-Cohen, 2003, 2005; Kikuchi, 1998; Nazario, 2005). This difference could underlie growing evidence that women tend to be better at multitasking than men (Burns, 2000).…”

Relationship between Sex-role Identity and Functional Cerebral Lateralization

“…Males may have greater functional cerebral lateralization (FCL) compared with females (Kimura, 1992;Kikuchi, 1998) in humans. Although sexual differences in FCL have been shown in functional magnetic resonance imaging (fMRI) studies (Levin et al, 1998;Baxter et al, 2003), greater FCL in males has not been reported in fMRI responses (Gur et al, 2000).…”

“…Sex-role identity (SRI) may be related to FCL. Sex steroidal hormones have been identified as a major factor in sexual differentiation of brain function (Toran-Allerand, 1984;Kimura, 1992;Kikuchi, 1998). On reviewing the relationships between sex steroidal hormones and FCL, Wisniewski (1998) concluded that testosterone is the most likely candidate to influence FCL.…”