Sex difference in behaviour and relevant neural substances

Question 1

what do sex differences refer to ?

Answer 1

• difference between the average male and the average female
• the range of differences within each sex usually is larger than the average difference between the sexes. - Therefore, identification of a sex difference acknowledges mean differences, but may allow one to predict very little about a specific individual’s performance on the basis of sex alone

Question 2

Heterosexual mating behaviour in mammals

Answer 2

• for mating to start 3 factors are needed, attractivity, proceptivity and receptivity
• if they’ re met you will have courting behaviour which leads to mating behaviour
• testosterone is necessary in males for mating to occur
• mating behaviour is particularly dependent on the menstrual cycle which controls the 3 factors above

Question 3

Reproductive and hormonal cycles in female mammals

Answer 3

• pregnancy only possible during a certain time of the cycle around ovulation (when estrogen and progesterone levels are high)
• female sexual behaviour is linked with the reproductive cycle and controlled by the hormonal fluctuations
• females can mate only during a certain time of the cycle around ovulation (behavioural estrous), except for primate females who can mate at any time. However in primates attractiveness, receptivity and perceptivity appear to be modulated in the hormonal cycle

Question 4

spinal mechanisms relevant to male copulatory behaviour in rats

Answer 4

Spinal nucleus of the bulbocavernosus (SNB)
- collection of motor neurons in the lower lumbar spinal chord; controls the bulbocavernosus muscle at the base of the penis
- these motorneurons and muscles are necessary for normal penile reflexes that are important for successful copulation
- they are absent of substantially reduced in size/number in adult females as compared to males

Question 5

Interaction of ‘nature’ and ‘nurture’: testosterone exerts some masculinising effects on SNB and sexual behaviour via the rat mother

Answer 5

• Rat mothers are stimulated to lick their male pups more often than their female pups because of testosterone in urine.
• Such anogenital licking contributes to normal male sexual behaviour in the adult and to a normal number of SNB neurons.

Question 6

what are sex circuits?

Answer 6

• contain sex hormone receptors, and these are critical for sex differences in mating behaviour: testosterone for male behaviour, estradiol and progestorone for female behaviour.
• Several components of these circuits show sex differences

Question 7

Sexually dimorphic nucleus of the preoptic area (SDN-POA) and posterodorsal medial amygdala (MePD)

Answer 7

• SDN-POA is masculinised by testosterone during a critical perinatal period.
• MePD volume and cell size depend on testosterone action in adulthood.

Question 8

Sex differences in human homologue to rodent spinal nucleus of the bulbocavernosus (SNB)
Forger & Breedlove, 1986

Answer 8

• humans have a similar motorneuron muscle that stimulate the penis muscle

Question 9

Sex differences in human preoptic area (POA) of the hypothalamus, Fliers & Swaab, 1985

Answer 9

• One nucleus in the POA of hypothalamus was larger in volume and cell number in males than in females.
• Hence, authors named the nucleus SDN.

Question 10

replication of Fliers & Swaab, 1985
Allen et al, 1989

Answer 10

• Studied four nuclei in the POA, which they named interstitial nuclei of the anterior hypothalamus (INAH) 1-4.
• INAH1 corresponded to SDN of Fliers&Swaab (1985), but did not differ between sexes.
• INAH4 also did not differ.
• INAH2 and 3 were larger in men than in females.

Question 11

LeVay, 1991 Sex differences in human preoptic area (POA) of the hypothalamus

Answer 11

• Found no significant sex differences in INAH1,2, and 4.
• Replicated that INAH3 was larger in heterosexual men than in women.
• Found additionally that INAH3 did not differ between homosexual men and heterosexual women.

OVERALL some evidence for sex difference in hypothalamus but research is unclear

Question 12

Sex differences in aggressive behaviour Arnold et al, 1993

Answer 12

• behaviour which involves threat or attack on other individuals
• aggression is not a unitary concept, some aspects of aggression are strongly related to reproductive behaviour e.g. competition for a mating partner
• In rodents, it has been shown that these aspects of aggression are mediated by brain regions that overlap with regions implicated in reproductive behaviour
• they are sex dependent and under the influence of sex steroids (there is particularly strong evidence for a role of testosterone).

Question 13

sex differences in aggressive behaviour in humans

Answer 13

• evidence for some aspects of aggression being sexually dimorphic
• one example finding that effect size differences in ratings of aggression and competitiveness based on questionnaire responses
• found statistically significant differences between m and f score on physical aggression, verbal aggression and interpersonal competitveness
• Testosterone has been suggested to contribute to these sex differences by acting on the brain, and some direct evidence supports this suggestion (Pasterski et al., 2007)

Question 14

sex differences in cognitive functions

Answer 14

• on average there is consistent evidence that women show advantages over men for perceptual speed, visual memory, verbal fluency and fine motor control
• males show an advantage over women for spatial rotation, paper folding, target accuracy and embedded figures

Question 15

Better place learning and navigation in males than in females –
Example study in rats (Markowska, 1999)

Answer 15

• water maze
• rats swim to find floating platform
• usse various things to measure: how fast they get there, distance travelled, heading angle
• males tend to have a slight advantage

Question 16

Better place learning and navigation in males than in females –
Example study in humans (Astur et al., 1998, Behav. Brain Res. 93:185)

Question 17

brain mechanisms which underlie Sex differences in place learning and navigation and relevant neural substrates

Answer 17

• in voles, evidence that it has evolved through ecological pressure
• only exist in polygamous species in which males range more widely than females in the field
• correlate with a larger hippocampus
• Sex differences in the hippocampus have also been found in rats and men (humans) - even though in rodents, the hippocampus tends to be larger in males than in females, whereas in humans the opposite is the case → origin of sex differences not clear

Question 18

sex difference hippocampus could be to do with hippocampal recruitment

Answer 18

• human MRI scan suggest that rather than size or volume
• the diferential recruitment of how they use their hippocampus could be important
• ps do place learning in a visual maze with a brain scan

Question 19

Sex differences in mental rotation and water jar task
Gladue & Bailey, 1995

Answer 19

• Mental rotation: 20 items with two correct and two incorrect choices each; 1 point per correct choice; maximum score 40.
• Water jar task: 10 items, consisting of jar tilted at different angles; subjects required to draw water line assuming jar is half full; maximum score 10 correct (drawn line within 5 deg of accurate water level).

Question 20

Sex differences in rapid place learning and mental rotation

Answer 20

• 60 females, 63 males – large sample size giving about 80% power to show signficant difference with an effect size of 0.5 (note: many published studies are underpowered)
• Although men were on average better on both tests, performance measures on place learning and mental rotation test did not significantly correlate (F1,121=2.11, p=0.15, r=0.13). This implies that sex differences on these two tests are likely to rely on different neuro-psychological mechanisms

Question 21

can anything be concluded between sex difference in the brain and sexual behaviour?

Answer 21

no, brain sites not primarily associated with sexual behaviour