We know that male and female brains are different. Structural difference between the
male and the female brain - sexual dimorphism - has been long detected
morphologically in numerous brain structures including cell groups in the area
critical to most hormonal, vegetative, emotional and reproductive responses in our
behavior - the hypothalamus, and other deep brain structures. Recent neuro-imaging
studies in the living brain identified sex differences in brain activity in various areas
of the brain. Some of these areas are associated with language which in males appears
to be highly lateralized in the lower left part of the frontal cortex, while in females the
active areas are diffused between left and right parts of the lower frontal cortex.
... Another question is how do sex differences and sexual orientation develop?
Experimental alteration of sex hormones concentration during development alters
sexual behavior. Exposing females to androgen just before birth and blocking
testosterone in males influences behavioral sex differences and differentiation of
genitalia. Remarkably, female rats exposed to exogenous androgens during the
perinatal period develop a masculine peripheral and brain characteristics. Deprived of
androgen, young male monkeys, for example, spend more time with their mothers
then their peers who also display seven times the blood concentration of
testosterone. It is now thought that it is predominantly testosterone that determines
the masculine morphology of the brain at the early stages of development. Lack of
testosterone determines a feminine brain. Any environmental aspect that may
influence secretion of testosterone in early development could also influence the
brain differentiation process. For example maternal stress has been shown to result in
more feminine morphology of male rats brains.
... Morphologically, in the developing human the sexually dimorphic nucleus (In) of
the MPO has been first identified at 16 weeks of development and it is thought that it
develops evenly in males and females up until 2 years of age after which many cells of
the female but not the male die to give the MPO sexual dimorphism. This
information may help to determine the critical time for differentiation of our sexual
behavior. In conclusion, the sexual dimorphism between male and female brains
includes structures directly involved in regulation of sexual behavior including the
medial preoptic hypothalamic nucleus. The mechanism of sexual differentiation of
the brain and MPO is most likely based on hormonal interactions during crucial
period of fetal and postnatal development.
Gender dimorphism in brain. NIDA Res Monogr. 1986; 65 : 49 - 57. Review. No abstract
available. PMID: 3016544 [PubMed - indexed for MEDLINE] Science, Vol 228, Issue
4703, 1112-1115 © 1985 by American Association for the Advancement of Science
__