"We studied general intelligence, which is the same between men and women," said Richard Haier, lead researcher and professor of psychology at the Department of Pediatrics at University of California, Irvine. "But we looked at structural brain differences and found that gray and white matter areas differed. This suggests to us that the brain has different ways to accomplish the same thing in men and women."
Gray matter is where information is processed in the brain. White matter is a bundle of fibers that contain connections among brain cells.
"The connections among neurons might be better in women," Haier theorized. "Women's brains may be more efficient."
Women and men perform equally well on intelligence tests, but a growing body of research shows that the brains of women and men process information differently at a biological level. More studies are needed to understand the functional effects of these differences.
Previous studies have shown that, in general, men seem to perform better on tasks that require spatial reasoning and advanced mathematical skills; whereas women outperform men in areas including verbal reasoning and memory.
These differences may explain why some women and men often take different career paths.
"The difference in the number of women in high end mathematical reasoning careers may be a reflection of differences in gray and white matter," Haier said. Women may gravitate toward careers involved more with verbal reasoning. But because there are no apparent sex differences in measures of intelligence and intellectual capacities, other factors may play a role in career choices.
There is a tremendous amount of overlap between the abilities of men and women, so it is important to examine cultural, social and economic influences as well.
In many countries, for example, the difference in performance in science and mathematics between boys and girls is not statistically significant. This implies that factors beyond brain structure play a role.
"There is so much overlap between the abilities of men and women that we cannot predict an individual's performance solely on the basis of whether they are male or female," Sherry Marts, vice president of scientific affairs for the Society for Women's Health Research said. "We must be careful to not over apply generalizations about brain structure to individuals."
Marts points to social and environmental factors as indicators of brain performance.
"In addition to biological sex," Marts said, "many other factors have an impact on brain development. Beginning with the environment in uterus and continuing throughout an individual's life, the body's internal environment combines with external conditions such as nutrition, physical activity, parental educational levels and the availability of educational opportunities to have a profound impact on brain development and function."
The UC Irvine study may also help elucidate gender differences in neurological diseases such as Alzheimer's.
"You may not see the symptoms of Alzheimer's disease in women as early in the disease process as you would in men," Haier said. Stronger verbal and memory skills in women may explain why some women are diagnosed later with the disease than men. In addition, certain diseases that cause brain cell loss in the cerebral cortex are more damaging to women because women appear to have a lower number of brain cells in that specific area of the brain than men.
There are gender differences in certain brain injuries as well. Frontal brain injuries can be more serious in women: "cognitive impairment is greater in women," Haier said. These types of injuries can be more harmful to the intelligence and cognitive processing of women than men.
From intelligence to illness and injuries, additional brain research holds the key to understanding much of human health and performance.