Sex and the Brain

Sex is Complex Sex – a person’s genetic biological characteristics: Male, female, a continuum between the two Sexual orientation – who you are attracted to: Opposite sex Same sex Both, neither Gender – social roles assigned by biological sex. Sexual identity – which sex you feel you are, independent of biology. Transsexuals, transvestites

Sexual Behavior Phases of sexual response are the same across species. Behavior results from many circuits, including hypothalamic activation, environmental inputs, hormones. The cortex decides what is and is not sexually stimulating. Sexual scripts – learned ways of responding in sexual situations.

Human Sexual Response

Sexual Dimorphisms Male and female brains differ because male and female bodies differ. The most distinct dimorphisms are related to reproductive behaviors. Many other sex differences have been claimed in the literature but these do not hold up well. Few cognitive differences exist in behavior once the impact of culture/socialization is controlled.

Sex Differences Claimed Women are better at verbal tasks – false. Men are better at spatial tasks and math – largely false. Women are more emotional, men are less emotional – false, except for expressivity. Women talk more than men – false. Men are more aggressive and more violent – true.

Impact of Testosterone Testosterone is not responsible for the masculinization of the male brain. Estrogen, binding to estradiol sites, results in masculinization of a developing fetus. Females do not produce surges of estrogen early in development and so miss this stage. Testosterone organizes masculinization early on and is needed again to trigger puberty.

Male vs Female Because hormones trigger masculinization, it is possible to have male females (genetically XX) and female males (genetically XY). Genetic males with a defective androgen receptor will develop as female. Genetic females with congenital adrenal hyperplasia (CAH) have unusually large amounts of circulating androgens.

Homosexuality Defined as sexual attraction to members of the same sex. Large-scale studies show that neither early childhood experiences nor learning accounts for homsexuality. Postmortem studies suggest the SCN of the hypothalamus may be responsible. Hamer’s studies suggest a genetic basis.