[Neuroscience] Re: Gender Differences in the Human Brain

Bill via neur-sci%40net.bio.net (by connelly.bill from gmail.com)
Fri Aug 15 23:52:24 EST 2008

This was something I wrote a while ago for a semi scientific audience:
But it doesn't really say too much

To most people, the fact that men and women are frankly different, is
pretty obvious. However declaring that there are differences in the
brains of men and women has been decidedly unfashionable since some
time in the 1960s, presumably because if you say there are
differences, then someone has to have been dealt the better hand.

So first off, if you're offended by the suggestion the men and women
have different brains, please go back to 1450 and stop Johannes
Gutenberg inventing movable type printing, because I'm sure someone
who 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 for
idiots who think an episode of CSI is an educational experience, an
article by Seymour Levine summarized the extent of the known sex
differences in the brain. His answer was essentially none, apart from
in a little place called the hypothalamus, an evolutionarily ancient
structure that controls all sorts of things like body temperature,
food intake, sleep and sexual function. Cut forward 40 years and a lot
of things have changed, it's still a bad idea to say the word
"homosexual" when requesting funds from the US government, but the
list of brain differences between the sexes is as long as my arm. To
start with, men have bigger brains. Not really that surprising, as men
have pretty much bigger everythings, because men are just bigger.
However, before any men in the audience start celebrating, this
difference can largely be put down to differences in the volume of
white matter, rather than the grey matter in the cortex (white matter
being the wires that pass information to the cortical grey matter,
where the actual processing happens) [1]. But of course, when you look
at things in a more detailed fashion, you find that some cortical
regions are thicker in women (the primary sensory and motor cortexes,
that process incoming sensations from the skin, and outgoing motor
control) and some areas are thicker in men (a small area in the left
medial temporal lobe, that should be involved in dealing with visual
information) [2]. Is there any functional relevance to this? I would
be very careful is ascribing a purpose to this difference, but one
doesn't need look at brain scans to find real differences in the way
men and women think.

It is widely agreed that males perform spatial tasks more proficiently
than women. The mental rotation task is often claimed to be the most
divergent. This task involves the subject being shown an abstract
shape and then being required to pick the image that shows the object
rotated 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 cortex
more, while women use the frontal cortex [5]. Men are generally
expected to perform spatial perception (such as judgment of line
orientation), maze navigation, and targeting and intercepting tasks
better too [3, 4]. On the other hand, women excel at high interference
memory tasks, such as problems where one is shown a complex field of
objects, with a short period to memorize them, and then shown a
similar but subtlety different field, where objects may have been
moved or subtracted, and is then required to state the differences.

Biochemical differences abound too. Men seem to be about 50% faster at
synthesizing the neurotransmitter serotonin (a chemical which may
enhance mood and sleep), which may explain why women suffer from
approximately 2x the rate of depression [5]. Amphetamine releases more
dopamine in men than women, while women seem to have higher activity
in the proteins that inactive dopamine (both transporters and
metabolic enzymes) which may explain why men report to enjoy a dose of
amphetamine more than women and experience higher rates of dopamine
related disorders like schizophrenia, OCD and Tourette's [6, 7, 8].
The differences truly go on and on (get down to your local library and
read Nature Reviews Neuroscience 7, 477-484 (2006) for more).

I'd love to wow you with the fact that in the nucleus in the
hypothalamus that is 4 times as big in men as it is in women (called
INAH3), is much larger in gay men than in straight men, (i.e. gay men
have female brains) as was reported by LeVay in 1991 to much
excitement. However, subsequent attempts to repeat this finding have
failed [9, 10]. A similar paper reported that in an area of the brain
called the bed nucleus of the stria terminalis, that is also
significantly larger in men than women, male-to-females transsexuals
had a female sized nucleus [11]. Finally, a doubly exciting pair of
papers in PNAS showed that two putative pheromones, an androgen (which
men presumably excrete) and an estrogen (which women presumable
excrete), when smelt by females and males respectively, excites the
hypothalamus. Furthermore, the estrogen that excites male brains had
no effect on homosexual men, while they were excited by the androgen
that excited females [12]. This observation was reversed in homosexual
women, whose brain were excited by the estrogen that normally excites
male brains [13].

It really should be very obvious that men and women are different, we
evolved to do different things. Most animal species on earth have huge
differences between the sexes, why should we be any different?

On Aug 11, 4:11 pm, kiwasabi <kiwas... from gmail.com> wrote:
> Hey everybody,
> I'm a Game Designer who is very interested in Neuroscience. I have
> read around 8 or so books on the brain so far. I was wondering if you
> guys could answer a question for me: What are the differences between
> a female and male brain? I have read that males have better developed
> visuospatial skills while females have better developed social and
> communicative skills. What else is there that I'm missing (a ton, I'm
> sure ;))?
> Thanks,
> Adam

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