Genetic
Gonadal
Hormonal
Morphological
Behavioral (gender role behavior)
Identity

Control of
Sex Hormones neural inputs
Indirect
Loop
Hypothalamus
Short
Loop
GnRH
Adenohypophysis
LH, FSH
Direct
Loop
Testes or Ovaries
Testosterone or Estrogen &
Progesterone
Target tissues

Phenotypic differences between males and females
They can be: anatomical physiological behavioral cognitive
They can be: qualitative quantitative

• Organizational Effects
• structural
• sensitive period
• irreversible
• masculinization/defeminization
• Activational Effects
• act on existing structure
• no sensitive period
• reversible

testes differentiate ovaries differentiate

Bipotential tissues: Undifferentiated tissue that can differentiate into either a male or female form.
Sexual Dimophisms: Structures, functions or behaviors that differ qualitatively or quantitatively between the sexes.

Prototypical Experiment
(Males)
Castrate male hamster at birth
(before period of brain differentiation)
Test in adulthood inject with testosterone place with receptive female male typical behavior low mounting, intromission
(ejaculation not possible) inject with estrogen and progesterone place with male female-typical behavior high darting, ear-wiggling, lordosis

Prototypical Experiment
(Females)
Neuter female hamster at birth and inject with testosterone
(before period of brain differentiation)
Test in adulthood inject with testosterone place with receptive female male typical behavior high
(mounting) inject with estrogen and progesterone place with male female-typical behavior low
(ear-wiggling, darting, lordosis)

Kelley, D.B. (1988) Ann. Rev. Neurosci.,
11, 225-251.

♀

Differentiation of the Brain
Two processes both are dependent on fetal androgens
Masculinization
Induction of male characteristics
Defeminization
Suppression of female characteristics

Estradiol is the sex hormone primarily responsible for masculinization of the brain.

α-fetoprotein binds to estradiol extracellulary and prevents entry into cell

Steroid Hormones

cholesterol

Control of
Sex Hormones neural inputs
Indirect
Loop
Hypothalamus
Short
Loop
GnRH
Adenohypophysis
LH, FSH
Direct
Loop
Testes or Ovaries
Testosterone or Estrogen &
Progesterone
Target tissues

Control of
Stress Hormones neural inputs
(limbic system)
Indirect
Loop
Short
Loop
Hypothalamus
CRF
(aka CRH)
Adenohypophysis
Direct
Loop
Corticotrophin
(aka ACTH)
Adrenal Cortex
Cortisol or
Corticosterone
Target tissues
This is usually referred to as the “HPA axis,” but is now often called the “LHPA axis.”

cholesterol aromatase estradiol
5-alpha reductase
DHT
Suppose there is a deficiency of either
21-hydroxylase or 11β hydroxylase.

cholesterol

cholesterol aromatase estradiol
5-alpha reductase
DHT

Testosterone
5α reductase
Dihydrotesosterone

Studies of mathematically gifted
Effects of brain damage
Anatomical studies of brain laterality
Functional (fMRI) studies of brain laterality

♀
♂

Benbow, C.P., Lubinski, D., Shea, D.L. &
Eftekhari-Sanjani, H. (2000) Sex differences in mathematical reasoning ability at age 13:
Their status 20 years later. Psychological
Science, 11, 474-480.

Meta-analysis of data from 13 studies of unilaterally brain-damaged adult humans
Females Males Totals
Left
Positive
Right
Positive
Totals
15/111
(9%)
16/103
(16%)
31/214
(14%)
100/246
(41%)
120/276
(43%)
220/522
(42%)
115/357
(32)%
136/379
(36%)
Data from:
Inglis, J. & Lawson, J.S. (1981) Sex differences in the effects of unilateral brain damage on intelligence.
Science, 212, 693-695.

Geschwind, N. & Galaburda, A.S. (1987)
Cerebral lateralization.
Cambridge, MA:
MIT Press

McManus, I.C. & Bryden, M.P. (1991) Geschwind ’s theory of cerebral lateralization:
Developing a formal, causal model. Psych. Bull., 110, 237-253.

Control of
Sex Hormones neural inputs
Indirect
Loop
Hypothalamus
Short
Loop
GnRH
Adenohypophysis
LH, FSH
Direct
Loop
Testes or Ovaries
Testosterone or Estrogen &
Progesterone
Target tissues

perform well on verbal and motor tasks poorly on spatial tasks perform well on spatial tasks, poorly on motor and verbal tasks

Splenium de Lacoste-Utamsing, C. & Holloway, R.L. (1982)
Sexual dimorphism in the human corpus callosum.
Science, 216, 1431-1432.

Gladue, Green
& Hellman (1983)
Science, 225,
1496-1499.

Gladue, Green & Hellman (1983) Science, 225, 1496-1499.

LeVay, S. (1991) Science, 253, 1034-1037

Size related to sexual identity not sexual orientation