Gender Differences in the Human Brain II

To most people, the fact that men and women are frankly different, ispretty obvious. However declaring that there are differences in thebrains of men and women has been decidedly unfashionable since sometime in the 1960s, presumably because if you say there aredifferences, then someone has to have been dealt the better hand.So first off, if you're offended by the suggestion the men and womenhave different brains, please go back to 1450 and stop JohannesGutenberg inventing movable type printing, because I'm sure someonewho hates the truth as much as you must think that is a good idea.So back in 1966, when Scientific American wasn't tripe written foridiots who think an episode of CSI is an educational experience, anarticle by Seymour Levine summarized the extent of the known sexdifferences in the brain. His answer was essentially none, apart fromin a little place called the hypothalamus, an evolutionarily ancientstructure that controls all sorts of things like body temperature,food intake, sleep and sexual function. Cut forward 40 years and a lotof things have changed, it's still a bad idea to say the word"homosexual" when requesting funds from the US government, but thelist of brain differences between the sexes is as long as my arm. Tostart with, men have bigger brains. Not really that surprising, as menhave pretty much bigger everythings, because men are just bigger.However, before any men in the audience start celebrating, thisdifference can largely be put down to differences in the volume ofwhite matter, rather than the grey matter in the cortex (white matterbeing the wires that pass information to the cortical grey matter,where the actual processing happens) [1]. But of course, when you lookat things in a more detailed fashion, you find that some corticalregions are thicker in women (the primary sensory and motor cortexes,that process incoming sensations from the skin, and outgoing motorcontrol) and some areas are thicker in men (a small area in the leftmedial temporal lobe, that should be involved in dealing with visualinformation) [2]. Is there any functional relevance to this? I wouldbe very careful is ascribing a purpose to this difference, but onedoesn't need look at brain scans to find real differences in the waymen and women think.It is widely agreed that males perform spatial tasks more proficientlythan women. The mental rotation task is often claimed to be the mostdivergent. This task involves the subject being shown an abstractshape and then being required to pick the image that shows the objectrotated in unknown directions from several dummy images.Interestingly, it seems that women use different parts of their brain,when attempting mental rotation, men seem to use the parietal cortexmore, while women use the frontal cortex [5]. Men are generallyexpected to perform spatial perception (such as judgment of lineorientation), maze navigation, and targeting and intercepting tasksbetter too [3, 4]. On the other hand, women excel at high interferencememory tasks, such as problems where one is shown a complex field ofobjects, with a short period to memorize them, and then shown asimilar but subtlety different field, where objects may have beenmoved or subtracted, and is then required to state the differences.Biochemical differences abound too. Men seem to be about 50% faster atsynthesizing the neurotransmitter serotonin (a chemical which mayenhance mood and sleep), which may explain why women suffer fromapproximately 2x the rate of depression [5]. Amphetamine releases moredopamine in men than women, while women seem to have higher activityin the proteins that inactive dopamine (both transporters andmetabolic enzymes) which may explain why men report to enjoy a dose ofamphetamine more than women and experience higher rates of dopaminerelated disorders like schizophrenia, OCD and Tourette's [6, 7, 8].The differences truly go on and on (get down to your local library andread Nature Reviews Neuroscience 7, 477-484 (2006) for more).I'd love to wow you with the fact that in the nucleus in thehypothalamus that is 4 times as big in men as it is in women (calledINAH3), is much larger in gay men than in straight men, (i.e. gay menhave female brains) as was reported by LeVay in 1991 to muchexcitement. However, subsequent attempts to repeat this finding havefailed [9, 10]. A similar paper reported that in an area of the braincalled the bed nucleus of the stria terminalis, that is alsosignificantly larger in men than women, male-to-females transsexualshad a female sized nucleus [11]. Finally, a doubly exciting pair ofpapers in PNAS showed that two putative pheromones, an androgen (whichmen presumably excrete) and an estrogen (which women presumableexcrete), when smelt by females and males respectively, excites thehypothalamus. Furthermore, the estrogen that excites male brains hadno effect on homosexual men, while they were excited by the androgenthat excited females [12]. This observation was reversed in homosexualwomen, whose brain were excited by the estrogen that normally excitesmale brains [13].It really should be very obvious that men and women are different, weevolved to do different things. Most animal species on earth have hugedifferences between the sexes, why should we be any different?




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