In article <3irh14$noh at netaxs.com>, swallow at netaxs.com (Ruder Than You)
wrote:
> For the most part, this is all true. In most right-handed folks,
> the left hemisphere controls speech, and the same applies for about 70% of
> left handers.
> The right hemisphere CAN take over control of the lost speech in
> some cases, but not in all. Many patients with strokes aquire a global
> aspasia, often permanent. Men in particular tend to not recover. Woman
> have a much higer recovery rate from strokes than men, as they often have
> language not localized to either hemisphere, or are able to adapt more
> easily.
> As you noted though, if the damage to the left hemiosphere is
> severe enough, there is certainly no assurance of recovery beyond simple
> speech.
>
I just found this group, and don't know the history of this thread, so
my comments may be rehashes. (If so, sorry.) But here goes:
I think there are a few interesting points that I don't see mentioned yet:
First, there is a newly published study, using functional MRI methods,
that reports evidence in support of the greater lateralization in men
than in women. Shaywitz et al. (Nature, 373:607-609) found that men
showed unilateral left-sided activation of the inferior frontal gyrus
during a phonological-processing task, whereas women tended to show
bilateral activation. they discuss the results in relationship to
previous stroke-recovery studies that are referred to above.
Second, although the stroke and hemispherectomy studies recounted above
hold true for adults, the story in kids is much different. Maureen Dennis
and colleagues have shown that children who undergo left hemispherectomy
develop excellent language skills that can be distinguished from controls
only with very fine experimental measures. Similarly, children who
suffer strokes early in life also usually develop very good language.
The point here is that brain plasticity allows the right hemisphere to
subserve language, as long as it is asked to do so before it loses that
plasticity.
Lastly, I think the big question is *why* the left hemisphere seems to
be the preferred locus for language. This question doesn't yet have a
definitive answer. Some have hypothesized that it is generally better
able to process rapid temporal stimuli (e.g. the auditory signals that
constitute language) than the right hemisphere. But this remains to be
proven.
paul wang wang at crl.ucsd.edu
