On Tue, 31 Oct 2000, Michael David Lee wrote:
>
> I was talking to my class, 2nd year child development class,
> about the growth of the corpus callosum in early childhood.
> One student told me that she remembered from Intro Psych
> that she was told that it is actually thicker in women
> than it is in men. This difference apparently accounts for
> why men do not always say what is on their minds, whereas
> women tend to be more emotionally upfront about things.
Aside from the speculative application to alleged differences in
the way the sexes think, a debate has been raging concerning
corpus callosal differences between men and women. Kolb and
Whishaw (3rd ed. 1990, and there's probably a newer edition it
would be of interest to consult) summarize the debate. They say
(p. 386) that the main claim is that the posterior part of the CC
(the splenium) is larger in females than in males, and of a
different shape. K & W comment that this has not been confirmed
by either postmortem exam or MRI scans. The scorecard (before
1990) was five replications, six failures.
I did a quick PubMed search and came up with plenty of studies.
Of two of the most recent, one says "myth", the other says
"true". BTW, one difference I haven't checked recently which
probably holds up is that us lefties have larger CCs than
brain-deficient right-handers. Makes me proud to be sinister.
-Stephen
1: Neurosci Biobehav Rev 1997 Sep;21(5):581-601 Related Articles,
Books
Sex differences in the human corpus callosum: myth or reality?
Bishop KM, Wahlsten D
Department of Psychology, University of Alberta, Edmonton,
Canada.
It has been claimed that the human corpus callosum shows sex
differences, and in particular that the splenium (the posterior
portion) is larger in women than in men. Data collected before
1910 from cadavers indicate that, on average, males have larger
brains than females and that the average size of their corpus
callosum is larger. A meta-analysis of 49 studies published since
1980 reveals no significant sex difference in the size or shape
of the splenium of the corpus callosum, whether or not an
appropriate adjustment is made for brain size using analysis of
covariance or linear regression. It is argued that a simple ratio
of corpus callosum size to whole brain size is not an appropriate
way to analyse the data and can create a false impression of a
sex difference in the corpus callosum. The recent studies, most
of which used magnetic resonance imaging (MRI), confirm the
earlier findings of larger average brain size and overall corpus
callosum size for males. The widespread belief that women have a
larger splenium than men and consequently think differently is
untenable. Causes of and means to avoid such a false impression
in future research are discussed.
Neuroreport 1999 Apr 6;10(5):937-40 Related Articles, Books
Re-evaluation of sexual dimorphism in human corpus callosum.
Oka S, Miyamoto O, Janjua NA, Honjo-Fujiwara N, Ohkawa M, Nagao
S, Kondo H, Minami T, Toyoshima T, Itano T
Department of Oral Surgery, Kagawa Medical University, Miki,
Japan.
To study the sexual dimorphism of human corpus cauosum (CC), we
analyzed the midsaggital magnetic resonance imaging (MRI)
morphometry in 67 adults aged (mean+/-s.d.) 36.82+/-9.35 years.
Four specific angles of the CC were determined. All four angles
in 34 females and 33 age-matched males showed a significant
difference between females and males. These morphometric findings
confirm a gender difference in the orientation of corpus
callosum.
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Stephen Black, Ph.D. tel: (819) 822-9600 ext 2470
Department of Psychology fax: (819) 822-9661
Bishop's University e-mail: [EMAIL PROTECTED]
Lennoxville, QC
J1M 1Z7
Canada Department web page at http://www.ubishops.ca/ccc/div/soc/psy
Check out TIPS listserv for teachers of psychology at:
http://www.frostburg.edu/dept/psyc/southerly/tips/
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