"tsoon" <tsoon@mail.usyd.edu.au> writes:
> I've read that left-handed people are less lateralised than right-handed
> people (i.e. the left and right hemispheres are less specialised in
> particular faculties so there is an intermingling of functions throughout
> the brain).
Most left-handed people have a mixture of left and right hemisphere control of speech, although the left side is dominant in most cases - truly right-sided language is rare. The corups calossum is on average ~11% thicker in left-handers, which may perhaps facilitate cross-hemisphere communication and bilateral functioning.
> Since men are more likely to be left-handed than women, doesn't that imply
> that women are less lateralised than men?
Men have on average a thicker corpus calossum than women, but since female brains are smaller than male brains the relative size of the CC in relation to the language areas is larger in women. There is also a result I saw on a seminar showing that the parts of the CC correlate more with various intelligence measures in females than in males - possibly both hemispheres are more involved in processing the same task in females.
There is also Geschwind & Galaburda hypothesis that testosterone influences (from prenatal environment, and genetic biases or production and sensitivity) the lateralization; it delays the growth of the posterior left hemisphere, increasing the risk for dyslexia, stuttering, hyperactivity abd learning disorders as well as anomalous dominance leading to left-handedness, right-hemisphere language and increased mathematical and artistic ability. The hypothesis is unfortunately a bit hard to test, and the difference in handedness and other properties between men and women is much smaller than predicted.
(taken from Biological Psychology by James W. Kalat - a nice introduction highly recommended for all extropians with neuropsychological interest)
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