BN Unit 2 Exam: sex differences in brain and behaviour

Why is it important to study sex differences, according to the slides?

Medical research and care have been centered on male physiology (male cells, male mice, men)

Name diseases/areas where sex differences exist that research has overlooked.

Heart disease, cancer, pulmonary disease, stroke, Alzheimer's, flu A, liver disease, and pharmacokinetics (drug handling)

What is the difference between within-sex and between-sex variation?

Between-sex = difference in the average male vs female; within-sex = spread among individuals of one sex. Male and female distributions overlap, and within-sex variation is often larger than the average difference

What are the two kinds of sex differences in the brain?

Connectional (functional) and volumetric (structural)

What is a connectional (functional) sex difference?

A difference in the type or number of synapses or the size of a projection

What is a volumetric (structural) sex difference?

A difference in the size of a structure or nucleus between males and females

What does SDN-POA stand for?

Sexually dimorphic nucleus of the preoptic area

Which sex has the larger SDN-POA?

Males

What happens to the SDN-POA of a female given testosterone early in life?

It becomes male-sized (masculinized)

Do males and females start with different numbers of SDN-POA neurons?

No — they start with equal numbers

Why is the SDN-POA smaller in females (and early-castrated males)?

Its cells undergo apoptosis (programmed cell death)

How do androgens make the male SDN-POA larger?

They prevent apoptosis during a sensitive period

By what route does testosterone masculinize the SDN-POA?

Through estradiol — T is aromatized to estradiol in the brain, which acts on estrogen receptors

What does MePD stand for, and which sex has the larger one?

Posterodorsal medial amygdala; males (about 1.5× bigger)

What does RA stand for, in which animal is it studied, and which sex has the bigger one?

Robustus archistriatum (a song nucleus) in birds like zebra finches; males

List the brain regions that are larger in males (Male > Female).

SDN-POA, MePD, BNST (bed nucleus of the stria terminalis), and in zebra finches RA, Area X, HVC

Which brain region is larger in females?

AVPV (anteroventral periventricular nucleus)

What does the AVPV regulate?

Ovulation

What happens to the AVPV of neonatally castrated males?

It approaches female size

What does the AVPV show about testosterone and apoptosis?

T can either prevent apoptosis (SDN-POA) or promote it (AVPV)

What did the 2020 human brain studies use?

The Human Connectome Project (976 healthy adults) and UK Biobank (1,120 healthy adults) to map male–female gray matter differences

What does INAH stand for?

Interstitial nuclei of the anterior hypothalamus

Which INAH nucleus is larger in men than women?

INAH-3

What did postmortem studies (of men who died from AIDS) suggest about INAH-3 and sexual orientation?

INAH-3 is smaller in gay men than in straight men

What proportion of rams are male-oriented?

About 7–10% (most, ~55%, are female-oriented; others bisexual or asexual)

How do male-oriented rams behave in partner-preference tests?

They show precopulatory behaviors and mounts toward rams, and essentially none toward estrous ewes

What does oSDN stand for, and how does its size relate to partner preference in rams?

Ovine sexually dimorphic nucleus; male-oriented rams have a smaller oSDN than female-oriented rams (closer to ewe size)

What did the 2021 Scientific Reports study find?

Brain structure differences associated with sexual orientation in humans

What did Fernández-Guasti et al. (2000) show?

Sex differences in androgen receptor (AR) density in the human hypothalamus (greater in men)

What did Kuhnemann et al. (1994) show about estrogen receptors?

Sex differences in ER emerge early in development (rat)

What did Rainbow, Parsons & McEwen (1982) show?

Sex differences in progesterone receptor levels in the rat hypothalamus (higher in females)

What did Dumais & Veenema (2010) show about vasopressin?

Vasopressin receptor density is sexually dimorphic

What happens to vasopressin and aggression after castration?

Reduced vasopressin content in the BNST and reduced aggression

What hormone is AVT, and in what animal was it studied?

Arginine vasotocin (the non-mammalian vasopressin), studied in bullfrogs

What effect does AVT have on male bullfrogs?

Increased mating-call vocalization

What effect does AVT have on female bullfrogs?

No change in vocalization, but increased attention to the source of the mating call

Where are there sex differences in AVT receptors in bullfrogs?

In the hypothalamus, amygdala, and other regions

Why is birdsong a useful model of sexual dimorphism?

It's a sexually dimorphic behavior directly influenced by structural brain differences

What happens in the sensory stage of song learning?

Young birds hear and memorize the songs of adults

What happens in the sensorimotor stage of song learning?

The bird tries to reproduce the memorized song through trial-and-error and highly repetitive practice

What does it mean for a song to be "crystallized," and which species does this?

Fixed and impervious to change; zebra finches (other species can keep modifying song)

What is the function of the posterior descending pathway?

Song production

Trace the posterior descending pathway.

HVC (high vocal center) → RA → nXIIts (directly, or via the dorsomedial nucleus intercollicularis) → syrinx

What is the syrinx?

The bird's vocal production organ

What happens if the posterior descending pathway is lesioned?

Song production deficits

What is the function of the anterior forebrain pathway ("recursive loop")?

Song learning

Trace the anterior forebrain pathway.

HVC → Area X → medial nucleus of the dorsolateral thalamus (DLM) → LMAN (lateral magnocellular nucleus of the anterior neostriatum) → RA

What happens if the anterior forebrain pathway is lesioned?

Song abnormalities (problems learning song)

What happens to the LMAN after the song has been learned?

It shrinks, even as the brain continues to grow

How much larger are RA and HVC in male vs female zebra finches?

Up to 6× larger in males

What is unusual about Area X in female zebra finches?

It cannot be discerned at all

At the neuron level, how do male song nuclei differ from female ones?

Larger and more numerous neurons

How do song-nucleus sex differences vary across species?

Extreme in zebra finches, less extreme in canaries, almost nonexistent in bay wrens (where females also sing)

How is the birdsong system organized and activated?

Organized by estrogens, activated by androgens

In primate play, which behaviors do males show more than females?

Initiating play, threat behaviors (lunges, grunts, open-mouthed stares), rough-and-tumble/simulated fighting, pursuit play

What did the "gender and toys" slide show about monkeys?

Sex differences in toy preference in nonhuman primates (males tend toward wheeled toys, females toward dolls/plush)

What happened when pregnant monkeys were given androgen?

Daughters had masculinized genitalia — originally called pseudohermaphrodites, now called prenatally androgenized females

How did prenatally androgenized female monkeys compare in rough-and-tumble play?

Intermediate between males and control females

How did prenatally androgenized female monkeys compare in pursuit play?

Intermediate between males and control females

Was the play change in androgenized females due to their masculinized genitals?

No

Did postnatal endocrine manipulations change monkey play behavior?

No — the effect is prenatal (organizational)

Besides prenatal hormones, what is required for normal play behavior?

Appropriate social stimulation (organization by hormones + environment = normal play)

How do girls with CAH play compared to other girls?

Masculinized/defeminized play behaviors

How did girls exposed to prenatal progestins (with androgenic effects) score?

Higher on aggression, high-energy play, and athleticism

What is the overall conclusion of the play studies?

Gonadal steroid hormones contribute to sex differences in play behavior

What sex differences were found in colors used in children's freestyle drawings?

Boys used more dark/cool colors (e.g., black, blue, gray); girls used more warm/bright colors (pink, purple, red, orange)

What sex differences were found in motifs in children's drawings?

Boys drew mostly moving objects (vehicles, trains, aircraft: ~92%); girls drew mostly people (~97%), flowers, butterflies, sun

How did drawings of girls with CAH compare?

More boy-typical: more moving objects/vehicles and darker colors