Female brains know how to fold 'em.

Thanks to their inherently larger bodies, men typically possess larger brains than women do. Size isn't everything, though. Women compensate for the smaller overall volume of their brains by squeezing more folds into some of the space than men do, a new brain-imaging study suggests.

Only women display a multitude of folds in the surface tissue of certain parts of the brain's outer layer, or cortex, Arthur W. Toga of the University of California, Los Angeles School of Medicine and his colleagues have found. These previously unnoticed pockets of bunched-up cortical tissue indicate that women's brains have a much-larger surface area than scientists had typically assumed, Toga's group concludes in the August Nature Neuroscience.

The investigators used a magnetic resonance imaging scanner to generate three-dimensional representations of the brain's surface in 30 men and 30 women, all healthy and ranging in age from 20 to 30. The team then measured the average number of folds in cortical tissue across all 60 brains.

No brain area in men exhibited a superior number of folds. But in the women's brains, there was substantially more cortical folding than in the men's brains in two regions--at the top of the frontal lobes and in the parietal lobes, toward the back of the brain. It's not yet known whether these brain differences are linked to any differences in cognitive skills--such as verbal fluency--in which women outperform men, the researchers say.--B.B.