Sex Hormones, the brain and behavior
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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
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