Is there any difference between male and female brains?

While specific parts show
sex differences, an individual brain only
rarely has all "male" traits or all
"female" traits, researchers report.
It's more likely to be a mixed bag:
some things are more common in
women, some more common in men,
and some are common in both.
That argues against the idea that brains
can be neatly divided into two sex-
based categories, Daphna Joel of Tel-
Aviv University and co-authors
conclude.
Both male and female zones
They published their work in a paper
released on Monday by the
Proceedings of the National Academy
of Sciences.
They used MRI scans of more than
1,400 brains, focusing on anatomy
rather than how brains work. They
scored variable traits like tissue
thickness or volume in different parts
of the brain.
They focused on traits that showed the
biggest sex differences, dividing the
scores into a predominantly male zone,
a predominantly female zone, and an
intermediate range.
The key question: How often did a
brain end up in just one of those three?
Such consistency turned out to be
unusual, generally found in 6 percent
or less of brains across analyses of
several sets of data. It was much more
common for an individual to score in
both the male and female zones than
to show a lineup that indicated only
one sex or the other.
The researchers also used a similar
approach to analyse psychological and
behavioural scores from two prior
studies that covered more than 5,000
participants, and again got similar
results.
Overall, the results show "human
brains do not belong to one of two
distinct categories", male and female,
the researchers concluded.
Larry Cahill, a neuroscientist at the
University of California, Irvine, who
didn't participate in the new study,
said he agreed that brains contain
varying mixtures of male and female
anatomical traits. But that doesn't rule
out differences in how the brains of
the two sexes work, he said.
There's "a mountain of evidence
proving the importance of sex
influences at all levels of mammalian
brain function", he said.
That work shows how much sex must
matter, "even when we are not clear
exactly how", he said in an email.