Sex and the Brain

1
Sex and the Brain
2
Sex is Complex

• Sex a persons 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

3
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.

4
Human Sexual Response
5
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.

6
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.

7
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.

8
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.

9
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.
• Hamers studies suggest a genetic basis.