Sex Hormones,the brain

and behavior

Definitions of Sex

GeneticGonadalHormonalMorphological

Behavioral (gender role behavior)Identity

Hypothalamus

Adenohypophysis

Testes or Ovaries

Target tissues

Control ofSex Hormones

IndirectLoop

ShortLoop

DirectLoop

GnRH

LH, FSH

Testosterone or Estrogen &Progesterone

neural inputs

Sexual Dimorphisms

Phenotypic differencesbetween males and females

They can be:anatomicalphysiologicalbehavioralcognitive

They can be:qualitativequantitative

Effects of Sex Hormones

• 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 tissuethat can differentiate into either a male orfemale form.

Sexual Dimophisms: Structures, functionsor behaviors that differ qualitatively or quantitatively between the sexes.

Castrate male hamster at birth

Prototypical Experiment(Males)

(before period of brain differentiation)

Test in adulthood

place with receptive female

inject with testosterone

male typical behavior low

mounting, intromission (ejaculation not possible)

female-typical behavior high

darting, ear-wiggling, lordosis

place with male

inject with estrogen and progesterone

Neuter female hamster at birth andinject with testosterone

Prototypical Experiment(Females)

(before period of brain differentiation)

Test in adulthood

place with receptive femaleinject with testosterone

male typical behavior high (mounting)

female-typical behavior low (ear-wiggling, darting, lordosis)

place with male

inject with estrogen and progesterone

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

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Differentiation of the Brain

MasculinizationInduction of male characteristics

DefeminizationSuppression of female characteristics

Two processes

both are dependent on fetal androgens

Estradiol is the sexhormone primarilyresponsible formasculinization ofthe brain.

Why aren’t all femalesmasculinized?

α-fetoproteinbinds to estradiol extracellularyand prevents entry into cell

Steroid Hormones

cholesterol

Hypothalamus

Adenohypophysis

Testes or Ovaries

Target tissues

Control ofSex Hormones

IndirectLoop

ShortLoop

DirectLoop

GnRH

LH, FSH

Testosterone or Estrogen &Progesterone

neural inputs

Hypothalamus

Adenohypophysis

Adrenal Cortex

Target tissues

Control ofStress Hormones

IndirectLoop

ShortLoop

DirectLoop

CRF(aka CRH)

Corticotrophin(aka ACTH)

Cortisol or Corticosterone

neural inputs(limbic system)

This is usually referred to as the “HPA axis,”but is now often called the “LHPA axis.”

estradiol

aromatase 5-alphareductase

cholesterol

DHT

Suppose there is a deficiency of either21-hydroxylase or 11-β hydroxylase.

cholesterol

estradiol

aromatase5-alphareductase

cholesterol

DHT

5-αreductase

Testosterone

Dihydrotesosterone

Sex differences in cognition

Studies of mathematically gifted

Effects of brain damage

Anatomical studies of brain laterality

Functional (fMRI) studies of brain laterality

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Benbow20 year follow-up

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

Brain Laterality

Females Males Totals

Left Positive

15/111(9%)

100/246(41%)

115/357(32)%

Right Positive

16/103(16%)

120/276(43%)

136/379(36%)

Totals 31/214(14%)

220/522(42%)

Data from:Inglis, J. & Lawson, J.S. (1981) Sex differences in the effects of unilateral brain damage on intelligence. Science, 212, 693-695.

Meta-analysis of data from 13 studies of unilaterally brain-damaged adult humans

Geshwind’s Theory of

Cerebral Lateralization

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.

Hypothalamus

Adenohypophysis

Testes or Ovaries

Target tissues

Control ofSex Hormones

IndirectLoop

ShortLoop

DirectLoop

GnRH

LH, FSH

Testosterone or Estrogen &Progesterone

neural inputs

perform well on verbal and motor taskspoorly on spatial tasks

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

Activational Effects of SexHormones on Cognition

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

Splenium

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 identitynot sexual orientation