SEX DIFFERENCES START EARLY
By Sean Henahan, Access Excellence
Sex differences in brain organization occur
earlier in humans than previously believed according to new
research from the University at Buffalo presented at a conference
of the Society for Psychophysiological Research.
Neuroscientists there have demonstrated for the first time that
differences in the way the male and female brains process
information are present early in life, and are not laid down
during the hormonal surges of puberty, as previously thought. The
researchers also have pinpointed for the first time the areas of
the brain in prepubertal children that are involved in the
performance of certain tasks.
The findings may lead to a better understanding of why boys are
more likely to develop language-related disabilities such as
dyslexia and stuttering, and why girls are more likely to develop
"nonlanguage" problems such as math disability.
The researchers stress that their findings indicate a difference
in brain organization between the sexes, not superiority or
inferiority. Furthermore, not all boys and girls show these
differences, they state.
"We wanted to answer the question 'Is there a brain organization
that is developed very early based on hormonal expression
prenatally and early postnatally? Hormones are known to affect
brain development and certain types of cognitive functions in
animals. It has been thought that in humans, differences in
cognitive function between the sexes emerge during puberty. We
hypothesized that these differences are laid down before and
shortly after birth." said David Shucard, UB professor of
neurology, pediatrics and psychology.
In the present investigation, prepubertal children were studied
to determine if behavioral and neurophysiological evidence is
present to support this hypothesis, and to define the brain areas
most involved in two specific tasks -- object-recognition memory
and spatial-localization memory.
The study is part of a large, multi-year NIH-funded project
looking at the role of hormones in brain organization in normal
pre- and post-pubertal children and in girls with Turner's
syndrome, a genetic disorder that affects the development of
secondary sex characteristics. The present study involved only
Using an electrophysiologic technique called probe
auditory-evoked potentials to locate and measure brain activity,
the researchers recorded brain responses of 12 male and 12 female
8-12-year-olds, via 20 electrodes attached to the scalp, while
they did face matching and dot-location matching, two tasks
requiring spatial reasoning and memory.
The study produced two previously unreported findings. First, the
parietal lobes of the cortex were more involved than other areas
of the brain in performing the spatial tasks in prepubertal boys
and girls, a finding other investigators have seen in adults.
Second, even at this age, the patterns of brain activity were
different between boys and girls when they performed spatial
tasks. During the face-memory task, males showed stronger
involvement of the right parietal lobe than the left, while in
females, right and left parietals showed nearly equal activation.
The dot-memory task showed a similar pattern of response in males
and females, but the difference was not as striking.
"As a result of our findings, we know that these differences
exist before puberty," said Janet Shucard, UB research assistant
professor of neurology. "Since it is also known that the only
other period of dramatic hormonal activity occurs around the time
of birth and shortly thereafter, we believe that it is this early
exposure of the brain hormones that is responsible for these
cognitive sex differences."
The Shucards note that patterns of brain activity can be modified
slightly through the activating effect of hormones that begins
during adolescence, even though the basic background has been
laid down much earlier.
Related information on the
Ancient Y Chromosome