1. Chapter 17 Sex and the Brain

2. Introduction Influence of brain on sex hormones
Sexual and reproductive behaviors
Male and female brains

3. Sex and Gender Concept of Gender
Biological characteristics and qualities
Gender-specific behaviors
Self-assessment
Societal expectations
Genetics
Hormones
Gender-identity
Perception of gender

4. Sex and Gender The Genetics of Sex Encodes testis-determining factor
Location of SRY on Y chromosome
Causes development of testes and testicular hormones
Makes fetus develop as male
Default pathway, female

5. Sex and Gender
Differentiation of fetus and development of gonads

6. The Hormonal Control of Sex
Hormones regulate physiological processes
Sex hormones: Steroids
Endocrine glands: Release sex hormones
Pituitary gland: Regulates endocrine glands
Structure affects function of hormone
Primary male hormones: testosterones
Primary female hormones: estradiols

7. The Hormonal Control of Sex
The Principle Male and Female Hormones
Men: High concentration of androgens
Women: High concentration of estrogens
Aromatization Process for Steroid Hormones:
Testosterone (androgen) + aromatase  estradiol (estrogen)

8. The Hormonal Control of Sex
Concentration of estradiol receptors in sagittal section of rat brain

9. The Hormonal Control of Sex
Males: Testes- release androgen
Testosterones – increase at puberty leads to development of secondary sex characteristics
Females: Ovaries- secrete estradiol (estrogens) and progesterone (progestins)
Blood concentrations of sex hormones vary
Males- levels fluctuate mildly during a 24 hour cycle
Females- levels fluctuate more extensively but on a
28-day cycle

10. The Hormonal Control of Sex
Pituitary and Hypothalamus Control of Sex Hormones
Gonadotropins: LH and FSH
Males- LH produces testosterone; FSH aids sperm maturation
Females- LH, FSH cause estrogen secretion

11. The Neural Basis of Sexual Behaviors
Mammalian Mating Strategies:
Polygyny
Male mates with many females
Polyandry
Female mates with many males
Monogamy
One mate

12. The Neural Basis of Sexual Behaviors
The Neurochemistry of Reproductive Behavior
Prairie voles: Solidly monogamous
Meadow voles: Asocial and promiscuous
Affected by oxytocin and vasopressin… Prairie voles exhibit higher levels of vasopressin and oxytocin…. Suggesting a role in the brain

13. The Neural Basis of Sexual Behaviors
Role of oxytocin and vasopressin receptors in reproductive behavior
Prairie voles display more oxytocin receptors in females and more vasopressin receptors in males
Meadow voles, fewer receptors in both sexes

14. Why and How Male and Female Brains Differ
Sexual Dimorphisms of the CNS
Sexually dimorphic nucleus (SDN)
INAH in humans analogous to rat SDN

15. Why and How Male and Female Brains Differ
Organizational effect of hormones
Tend to be irreversible
Activational effect of hormones
Tend to be temporary

16. Why and How Male and Female Brains Differ
An example of the activational effects of hormones… in the somatosensory cortex, the plasticity of the ventral surface for the nipples increases by ~100% to encourage lacation .
This increase in sensation is associated also with increases in prolactin, oxytocin, and a variety of birthing, parental care, and reproductive behaviors.

17. Why and How Male and Female Brains Differ
Sexual Orientation
INAH-3 - twice as large in heterosexual males compared to heterosexual females: Sexually dimorphic
INAH-3 in homosexual males: Similar in size to that in heterosexual females
INAH – 3 in homosexual females does not appear to differ from heterosexual females
See Levay, 1991.