Scientists at Johns Hopkins have discovered "striking" differences between men and women in a part of the brain linked with ability to estimate time, judge speed, visualize things three-dimensionally and solve mathematical problems. The differences, the researchers say, may underlie well-known trends that vary by sex, such as the fact that more men than women are architects, mathematicians and race-car drivers.
In a study reported in the Dec. 1, 1999, issue of the journal Cerebral Cortex, the researchers show that a brain region called the inferior parietal lobule, or IPL, is significantly larger overall in men than in women. The area is part of the cerebral cortex and appears on both sides of the brain, just above ear-level.
Also, there's a symmetry difference, with men having a larger left IPL than right. In women in the study, it's the right IPL that's somewhat larger, though the difference between the two sides of the brain is less obvious than in men, says psychiatrist Godfrey Pearlson, who headed the project.
"This is the same part of Albert Einstein's brain that was particularly large compared with controls," says Pearlson. "Scientists have noticed this region is also larger in the postmortem brains of other physicists and mathematicians."
In the study, researchers reviewed MRI scans of the brains of 15 closely matched men and women. They used new computer software created by Hopkins psychiatrist Patrick Barta to compare overall IPL volume by gender. The software lets scientists highlight the IPL by "painting" it in on computer images of each subject's brain; it then calculates a highly accurate volume. Researchers also compared IPL volumes on the left and the right sides of the brain. After allowances for men's larger overall head and brain size, men had roughly 6 percent more IPL tissue than women.
"The inferior parietal lobule is far more developed in people than in animals and has evolved relatively recently," says Pearlson. It allows the brain to process information from senses such as vision and touch, and enables the sort of thinking involved in selective attention and perception.
Studies link the right IPL with a working memory of spatial relationships, the ability to sense relationships between body parts and awareness of a person's own affect or feelings. The left IPL, Pearlson says, is more involved in perception, such as judging how fast something is moving, estimating time and having the ability to mentally rotate 3-D figures.
"To say this means men are automatically better at some things than women is a simplification," says Pearlson. "It's easy to find women who are fantastic at math and physics and men who excel in language skills. Only when we look at very large populations and look for slight but significant trends do we see the generalizations. There are plenty of exceptions, but there's also a grain of truth, revealed through the brain structure, that we think underlies some of the ways people characterize the sexes."
Earlier research by Pearlson showed that two crucial language areas in the frontal and temporal lobes of the brain were significantly larger in women, perhaps explaining their advantage in language-associated thought.
Other researchers in the study were Melissa Frederikse, Angela Lu and Elizabeth Aylward. Funding was through the National Institute on Aging.