Sex differences of the Brain

Stephan Anagnostaras stephan at psych.ucla.edu
Thu Dec 5 12:20:36 EST 1996


In article <01bbe17e$1cbe8f00$2d063bcb at skolb.granite.treko.net.au>, "Steve
Kolb" <skolb at treko.net.au> wrote:

> In their book  "BrainSex" , Anne Moir and David Jessel  showed that mens
> and
> womens brains  in fact are differant, basing  their  information on
> research done
> by many scientists around the world. 
> 
> I have always regarded men and women as equal but differant, this also 
> makes 
> sense from an evolutionary  point of view.
> 

Politics are amazing, especially the way people can use mathematical
terms in such a stunning way.  "Equal but different". So lets see,
does this mean the " = " sign and the "not equals" sign have the same
meaning? -- anyway, I get your drift:

Well, anyway, I think we all get your point, that the subjective value of
the things that mens and women's brains do is not different, even if the
actual ways they function is different.  In fact, Men's and Women's brains
are different; a decent source is LeVay's Sexual Brain book, or if you
would like I can point you to some scientific (i.e., journal article)
reviews. In humans, a few differences in structure have already been
reported (notably in the hypothalamus, corpus callosum, as well
as functional differences in Broca's and Wernicke's areas), whereas
in animals there are a number of larger differences in structure
(especially structures related to sexual behavior) as well as function
(eg., hippocampus). So women's and men's brains are really different.

Now, what this means for function is a different story.  Although the
structural differences seem quite striking (i.e., the data from
mens and women's brains sometimes show no overlap at all), the manifestation
of these differences in cognitive tests is quite small, with considerable
overlap. For example, when people broadly say "men do better in spatial
tests, women do better in verbal tests." this does not mean that "all men
do better on spatial tests," rather tha vast majority overlap. What it does
mean is that, on average, men do better; the same is true of verbal tests,
with only a few cognitive tests showing little overlap [the most notable:
dowel balancing, the ability to say it is perfectly staight up, favors
men :), and for women it is synonym generation, i.e., saying the same
thing over again in different ways :) ].  Now, it is probably the case
that these types of tasks recruit so many brain areas that the sex differences
are "washed out", and if you really found a task that relied heavily on a brain
area (only) with large sex differences you would see little overlap. Much of
this is in dispute, but in recent years in the scientific community
most people working in the field agree that structural/functional differences
in the brain probably underlie sex differences in cognitive performance
rather than differences in treatment (although most school psychologists
would probably disagree); this remains to be conclusively shown, however.
As far as sexual behavior, there is good agreement that this is probably
due to sex differences in the brain, at the very least in the hypothalamus.

Within animals, there are large sex differences in maze learning, fear
conditioning, open field activity, obviously sexual behavior, etc. To some
extent these differences have been attributed to sex differences in 
hippocampal morphology (size & shape) as well as physiology (e.g., long-term
potentiation).  Although it is likely the case that the human hippocampus
also has sex differences, I don't think this has been conclusively
demonstrated (although preliminary evidence is quite good).  

Anyway, there has been a reluctance to study sex differences within
psychology, one of which is political, and the other of which is related
to the older dogma within psychology known as the "general process
approach." This approach has tried to ignore even differences
among species, never mind sexes.  However, with good agreement about
what the general processes are (at least within learning), psychologists
are now also becoming interested (as ethologists have been for years) in
sex differences & evolution.  So, for this reason, you should see considerable
new research on things like learning & cognitive performance, whereas
much more work has been done in terms of sexual behavior already (primarily
by ethological and biological types).


Good luck, 
Stephan

> Does anyone here, working in this field,  dispute their findings ?  
> 
> Any information on the subject would be greatly appreciated.
> 
>                                 regards
> 
>                                   Steve Kolb
> 
>                                 skolb at treko.net.au



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