Psych - sex differences

first lecture of pain (im presuming) + second lecture + 3rd lmao + 4th hehe + 5th!

Principal Parts of a neurone

• Dendrites

• Soma (Cell body)

• Myelin Sheath

• Axon (inside myelin sheath)

• Terminal buttons

Difference between EPSP + IPSP

exhitory + inhibitory

Sex determination in mammals

• Located on the Y chromosome

• SRY gene turns fetal gonad into a testis - in absence of SRY gene gonad becomes ovary

Hormones

Early testis produces 2 hormones:

• Anti-mullerian Hormone (Defeminising)

• Androgens (Masculinising)

If these hormones aren’t present, the internal sex organs will develop into female sex organs

Development of internal sex organs

Precursor of female sex organs - Mullerian system

precurser of male - Wolffian system

• Anti-mullerian hormone removes Mullerian system - results in male internal sex organs

• No hormone - Wolffian system is removed and Mullerian system remains, as Wolffian system requires androgens

Development of external Genetalia

Dihydrotestosterone (DHT) is required for the develpoment of the male external sex organs

• Absence of DHT results in female organs

A person with Persistent Mullerian Duct Syndrome has…

Male external genitalia, with testes, male and female internal genitalia

The external genitalia of a person with androgen insensitivity syndrome are…

Female

Actions of hormones

Organisational;

• Effect remains after the hormone has been removed. Often occurs during a sensitive period (such as embryonic development)

Activational;

• Effect is reversible, depending on presence or absence of hormone

Puberty

• Organisational and activational role of sex hormones

• Development of secondary sexual characters

• Pubic and axillary hair are androgen (androstenedione) sensitive in both males and females

Onset of Puberty

• During childhood, sex hormone levels are almost undetectably low

• Developmental timing mechanisms starts puberty

• Sex differences in mechanisms and timing

Pre-pubertal period (In Hypothalamus)

• GABA/NPY neurons inhibit KNDy neurons - prevents them from stimulating GnRH neurons

Post-pubertal period

• GABA stops inhibiting - KNDy neurones stimulate GnRH

• (don’t know how this happens)

Gonadotropin Releasing Hormone (GnRH) starts off puberty

In hypothalamus are the GnRH releasing hormones - released into the bloodstream into the anterior portion of the pituitary gland - releases gonadotropins

Gonadotropins

Follicle Stimulating Hormone (FSH)

• Males

  • Sperm Production

• Females

  • Cause follicles to ripen

Luteinising Hormone (LH)

• Males

  • Testosterone Production

• Females

  • Induce ovulation and formation of Corpus Luteum

(lil summary) Hypothalamo-Pituitary-Gonadal (HPG) axis

• Hypothalamus: GnRH (gonadatropin-Releasing Hormone)

• (Anterior) Pituitary Gland: Gonadotropins (FSH, LH)

• Gonads:

  • Testies: Testostorone

  • Ovaries: Oestradiol, progesterone

HPG Axis - Feedback system

Regulates the gonadal hormones

• Eg regulates testosterone - when its released in the bloodstream it stimulates the anterior pituitary and hypothalamus (Negative feedback loop)

What are the consequences on the HPG axis of taking anabolic steroids?

• Testes make low amounts of testosterone

• The hypothalamus produces less GnRH

• Testes will shrink

The Menstrual Cycle: Ovulation

• Anterior pituitary gland releases FSH into ovary

• Growth of follicle

• release of Estradiol stimulates LH release from pituitary (from hypothalamus)

• LH stimulates Ovum release from follicle (ovulation - goes into Fallopian tube)

• The ruptured follicle develops into corpus luteum, releasing progesterone and Estradiol

• If ovum is not fertilised, progesterone and estriadiol levels fall and uterine walls sloughed off as menstrual flow

Examples of sexual differentiation

• Androgen Insensitivity Syndrome

• 5α-reductase deficiency

• Congenital Adrenal Hyperplasia

Androgen Insensitivity Syndrome

• Gonads develop as testes

• Androgen receptors do not work

• Testosterone cannot do its normal job

• 46, XY individuals develop anatomically as female, but without female genitalia

• Puberty is typically late, sometimes helped with hormone supplements

  • typically identify as a woman

Complete Androgen Insensitivity Syndrome in 46,XX individuals leads to…

Lack of pubic hair

5α-reductase deficiency

• 5α-reductase turns testosterone into DHT (Dihydrate Testosterone)

• DHT is crucial for prenatal external genital development

• 46,XY children are born with female external genitalia, but male internal genitalia

• At puberty, the high levels of testosterone can ‘mimic’ DHT

  • They develop male genitalia (“Guevedoces”)

  • After puberty, they mostly identify as men

Congenital Adrenal Hyperplasia

• Results in lower Cortisol levels

• causes more testosterone to be produced by the androgens

• not easy to identify in males at birth

• Most common cause of CAH is 21-hydroxylase deficiency (enzyme deficiency needed for synthesis of cortizol)

CAH in girls

• High levels of prenatal testosterone in girls

• Ambiguous external genitalia in girls

• Often treated once diagnosed

• Some 46,XX children assigned male at birth

  • 5% of CAH girls assigned female at birth have gender dysphoria

  • 12% of CAH “girls” assigned male at birth have gender dysphoria

Sex Differentiation in the Brain

Both structural and functional sex differences, due to:

• Hormones, (activational and organisational)

• Genetics (Genes on sex chromosomes)

• Environment (eg peers, culture)

Experimental manipulation possible in mice, not humans. Info in humans gathered from:

• Congenital Adrenal Hyperplasia in 46,XX

• Complete Androgen Insensitivity in 46,XY

• Hormone treatment in transgender individuals

Sex Differentiation in brain - Behavioural Differences

• Boys and girls have different toy preferences

• CAH 46,XX individuals have more masculine toy preferences

• CAIS 46,XY individuals typically have feminine toy preferences

• Correlation between play style and prenatal testosterone

• Men tend to be faster in spatial mental rotation tasks

• CAH 46,XX individuals perform better than non-CAH 46,XX individuals

• CAIS 46,XY individuals are indistinguishable from non-CAIS 46,XX individuals

  • Suggests a role of testosterone in spatial mental rotation

Sex diff in brain - Structural Differences

• Male brains are ~10% larger

• Female cortex is thicker (more grey matter)

• Males have larger white matter volume and subcortical structures

• CAIS 46,XY individuals have some features that are masculine (genetics), and some that are feminine (hormones or environment)

  • Sex differences in the brain are complex and specific, and due to many different causes

Sex Differences: Sexual Orientation

• One of the most extreme sex differences

• 90-95% of human males are attracted to human females exclusively (“gynophile”)

• 85-90% of human females are attracted to human males exclusively (“androphile”)

Sex differences in the brain that co-vary with sexual orientation in humans

• SCN larger in androphile individuals (Swaab & Hofman 1988)

• INAH-3 smaller in androphile individuals (Levay 1991)

• Anterior commissure larger in androphile individuals (Allen & Gorski 1992)

Brain differences

Could be:

• Causal to sexual orientation

• purely correlation, as indicators of other mechanisms (hormonal, genetic)

• Consequence of sexual orientation

Origins of Sex differences in brain and behaviour

• Experimental / Cultural Effects

• Activational Hormonal Effects

• Organisational Hormonal Effects

• Genetic Effects

Environmental effects on sex differences

• Influences on brain development

• Effects of practice

• Social effects

  Little to no evidence that this affects sexual orientation

Experience and Sexual orientation

• Most people feel their sexual orientation has always been this way

• No good evidence to support effects of parenting, learning, etc

• Evidence from other species (sheeps)

  • 8% of male sheep are exclusively interested in other males

  • Sexually Dimorphoc Nuclueus (SDN) of preoptic area is smaller in these males

  • Size of SDN is influenced by developmental T levels

Activational Hormonal Effects

• Variations with varying testosterone levels

• Variations with varying estradiol levels

• Variations with the menstrual cycle

• No differences detected in adulthood between different sexual orientations

  • Hormone fluctuations, manipulations, or treatments affect sexual motivation, but not orientation

Organisational Hormonal Effects

• There are two periods during development during which T is high in boys:

  • Weeks 8-24 of pregnancy

    • Early: external genitalia

    • Late: brain differentiation

  • First 3 months after birth

    • Potential further brain differentiation

• Correlations with measured prenatal hormones

• Correlations with adult correlates of prenatal hormones

• Conditions with varying prenatal hormone levels

  • Congenital Adrenal Hyperplasia (CAH)

  • Androgen Insensitivity Syndrome

Correlates of Embryonic T

• Cognitive performance

• Ratio of 2nd and 4th finger length (2D/4D)

• Oto-acoustic emissions

Cognitive Performance

• Verbal abilities are better in androphile men than gynophile men

• Visuo-spatial performance is worse in androphile men than gynophile men

• Mental rotation is faster in gynophile women than in androphile women

2D/4D ratios

• Sex differences in 2D/4D ratios

  • (male: 0.95, female: 0.97)

• Early testosterone dependent

• Butch lesbians have more masculine 2D/4D

• No consistent finding in androphile men, but may differ between sub-groups - 2D/4D correlates with gender non-conformity

Oto-acoustic emissions

• When stimulated with a click, ears make a sound back

• This is louder and more frequent in women (and females of other species)

• Early T-dependent in other species

• Gynophile women’s OAEs closer to gynophile men’s than androphile women’s

Organisational Role of Hormones

• Most evidence points towards a role of prenatal testosterone in developing as a gynophile adult

  • CAH females are also more likely to identify as a gynophile

Genetic effects

• Twin studies

• Genetic mapping

• Concern from an evolutionary angle

• Fraternal Birth Order effect

Twin Studies

• Higher concordance in monozygotic than dizygotic twins

• Estimates from 30-100%

• Possible higher concordance for women than men

Genetic mapping

• Androphilic men often have androphilic maternal uncles

• Suggests an X-chromosome inheritance pattern

• A region of the X-chromosome has been identified as related to sexual orientation

• Regions on other chromosomes have also been identified

Evolutionary Concerns

• Should homosexuals not have fewer offspring?

• How does a putative genetic basis not get selected out of the population then?

• Possible mechanisms for maintaining such genes:

  • Heterozygote advantage

  • Different effects in males vs females

  • Kin selection

Fraternal Birth Order Effect

• More likely to be a gay male if you have older gay brothers (from the same mother not adopted)

• Maternal Immune Hypothesis:

  • Mothers immune response to protein neuroligin 4 Y-linked predicts probability of having male-oriented son

Sexual Orientation: Conclusions

• Clear biological developmental influences

• No influence is absolute

• Sexual orientation can be influenced by a number of different factors

Gender Identity

• Gender identity has an even larger sex difference than sexual orientation

• Does not seem to be binary

• Childhood gender dysphoria does not always continue after puberty (does for ~40%)

• What influences gender identity?

  • Not a single ohenotype

  • Genetic predispositions ( there is a slide on this but i dont get it, its just an image )

  • Pre-transition brain differences

Pre-transitional brain differences

• Brain volumes are in line with natal sex

• MtF individuals show more feminine cortical thickness and white matter in some brain areas

• FtM individuals show more masculine basal ganglia and some white matter tracts

• Some aspects of brain anatomy are different from both cis males and cis females

Conclusions

• Genetic and hormonal factors cause sexual differentiation

• Different aspects of brain and behaviour can be
masculinized or feminized, leading to a wide diversity of
combinations of “gendered” traits