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SEX DIFFERENCES START EARLY

By Sean Henahan, Access Excellence


TORONTO, Ont.- 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 normal children.

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.


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