NEW YORK, May 20 (Reuters Health) -- The proportion of gray and white matter in the human brain differs considerably between the sexes, and this may explain why women perform better in verbal and memory tasks, while men do better in solving spatial problems, according to researchers at the University of Pennsylvania in Philadelphia..Their findings also show that women's brains, although usually smaller than men's, have relatively larger amounts of information-processing gray matter. This may help explain why the sexes score similarly on intelligence tests.

Using magnetic resonance imaging (MRI) techniques, Dr. Ruben Gur, a professor of psychology, and his team also found that men's brains have a relatively higher proportion of white matter than women.

In an interview with Reuters Health, Gur said he believes this is the first time the difference in proportional volume of gray and white matter has been examined in the sexes.

"It seems like it should have been obvious, but this is apparently new knowledge," he said. "Nobody really looked at sex differences by plotting cranial volume before."

Gray matter refers to the gray nervous tissue found in the brain and spinal cord. It is composed of neuron cell bodies and parts of nerve cells called axons, and it is the area involved in thinking and other higher cognitive tasks such as problem solving.

White matter, which is nervous system tissue that consists primarily of nerve fibers coated with a white, fatty substance known as myelin, is responsible for communication between different parts of the brain.

The discovery answers a question that has puzzled scientists for years. If greater head size indicates greater intelligence, why do women, who generally have smaller heads than men, perform equally well on intelligence tests?

The answer, suggests Gur and his colleagues, is that women's brains are more efficient. The greater proportion of gray matter provides them with a greater processing capacity.

These findings, from a study of young adults, 40 men and 40 women, could have implications for education and medicine, said Gur. It may explain why women perform certain verbal tasks better than men, while men, with their greater amount of white matter that provides for the transfer of information between distant regions of the brain, excel at spatial tasks.

"For education, this suggests that different strategies might work for men and women for cognitive and learning tasks. As we learn more about the neural networks that facilitate learning, the clearer the implications for education this information will become," he said.

Gur and his team suggest that more research on the anatomic differences "may have implications to brain disorders, in which sex differences have been noted in frequency and severity."

"In the area of medicine, we would assume that diseases that affect gray matter predominantly will affect men more adversely," Gur explained. "And of course, the inverse would apply for white matter and women. In stroke, for example, if it occurred in an area of gray or white matter, one could perhaps predict how serious the effects would be on the cognitive abilities of a man versus a woman."

SOURCE: The Journal of Neuroscience 1999;19

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