SEXUAL ORIENTATION AND ANATOMY OF TEH CORPUS CALLOSUM
Scamvougeras, et al.
An increased prevalence of left-handedness (defined as not exclusive
right hand preference) was found in gay men compared to the general
population McCormick & Witelson, 1991). Left-handedness and, by
inference, hemispheric functional asymmetry,was found also to be
correlated with increased cross-sectional area of the isthmus of the
corpus callosum in men (Witelson & Goldsmith, 1991). Based on these and
other finsdings it was hypothesized that the isthmus is larger in gay
men than in heterosexual men even when hand preference is controlled.
Eleven gay men and 10 heterosexual men matched for age and educational
level, all selected to be in good health and consistently right-handed,
underwent a research MR scanning procedure specifically designed for
this study. Callosal measurements were obtained from 4mm midsagittal
slices. Area measures of the total corpus callosum, the isthmus and
other subregions were obtained. The isthmus was larger in gay men by
13% (p = .05, one-tailed test). Similar results were found for the
anterior commissure (Allen & Groski, 1992). The isthmus interconnects
right and left parietotemporal regions involved with linguistic and
spatial functions, tasks on which gay and heterosexual men differ
(McCormick & Witelson, 1991). Our findings add to the evidence of a
neurobiological factor in the origin of male sexual orientation.
Moreover, our results indicate the sexual orientation is linked to
functional lateralization of higher cognitive functions and may be part
of a larger constellation of cortical and cognitive characteristics.
On Apr 4, 2006, at 11:25 AM, Stephen Black wrote:
Michael Sylvester was challenged about his remark of "talk" of an
association between the
corpus callosum and sexual orientation. He was asked for a reference.
He replied:
It either came from LeVay or check out a Brain/Mind video
I thought this was interesting, so I looked into it. There is no
published work, as far as I can
find, on the corpus callosum and sexual orientation. However, Allen
and Gorski (1992) did
report that the anterior commissure was larger in homosexual than in
heterosexual men.
The anterior commissure is a bundle of nerve fibers which, like the
corpus callosum,
connects the two hemispheres of the brain. However, it's smaller than
the corpus callosum
and deeper within the brain. Its function is largely unknown. So the
claim is close, but no
cigar.
Curiously, though, if the claim is googled rather than pubmedded,
references to such a
finding by (yes) the neurophysiologist Simon LeVay and the
neuropsychologist Sandra
Witelson turn up. For example, LeVay is described in an article by
Chandler Burr in the
_The Atlantic Monthly_ in March, 1993 as carrying out an MRI study of
the corpus callosum
and sexual orientation. Some reports are even more specific. An
article at the gayline
website (http://www.gayline.gen.nz/natural.htm) says that LeVay
discovered that the corpus
callosum "was bigger in gays than straight men".
Since I could find no such study, I went right to the top, and wrote
to Dr. LeVay. Through the
magic of the Internet, he replied almost immediately. He said he never
made any such
discovery and never published on the topic. He did say that at one
time he worked on an
MRI study, as reported by Burr, but they didn't obtain any clear
results and didn't publish it.
So where did the misinformation come from? Another site repeats the
exact passage I
found at the gayline website, but this time credits it to the book
"Mapping the Brain" by Rita
Carter, from where gayline probably copied it without attribution. We
have the book in our
library, but it's out at the moment, so I can't check to see how she
came to provide this
misinformation.
What about the claim about Sandra Witelson's finding (at McMaster,
from whence I come)?
For example, Maclean's Magazine (the Canadian _Time_ wannabe) for
January 22, 1996
(available on-line at the Canadian encyclopedia) says "Witelson and
her research partners
illustrated another dimension of brain differences in November, 1994.
In a study involving
21 people, they showed that part of the corpus callosum in the brains
of some homosexual
men was 13 percent larger than in the heterosexual men".
Seems too specific to be made up. But where's the pub? Dr. Witelson
hasn't yet replied to
my query. But I've discovered in the meantime that this refers to a
presentation she made
with Scamvougeras as first author at the Miami meeting of the Society
for Neuroscience in
1994. I can't get the abstract, but it was cited as recently as 1993
by Rahman and Wilson
who say the study was MRI and confirm the Maclean's account. Given the
potential interest
in such a finding, I find it peculiar that they never published it.
Stephen
References
Allen, L., & Gorski, R. (1992). Sexual orientation and the size of the
anterior commissure in
human brain. Proceedings of the National Academy of Science, 89,
7199-7202.
Rahman, Q., & Wilson, G. (2003). Born gay? The psychobiology of human
sexual
orientation. Personality and Individual Differences, 34, 1337-1382.
Scamvougeras, A., Witelson, S. et al (1994). Sexual orientation and
anatomy of the corpus
callosum. Society for Neuroscience Abstracts, 20, 1425.
______________________________
Stephen L. Black, Ph.D.
Department of Psychology
Bishop's University
Lennoxville, QC J1M 1Z7
Canada
[EMAIL PROTECTED]
Dept web page: www.ubishops.ca/ccc/div/soc/psy
TIPS discussion list for psychology teachers at:
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Steven M. Specht, Ph.D.
Associate Professor of Psychology
Utica College
Utica, NY 13502
(315) 792-3171
"Mice may be called large or small, and so may elephants, and it is
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