Female Brains Have More Folds

By Melissa Lee Phillips
Neuroscience for Kids Consultant
October 4, 2004
Women's brains may be smaller than men's, but the female brain packs an extra punch, says a study published in the August 2004 issue of Nature Neuroscience. Frontal and parietal regions of the cerebral cortex are more folded, or convoluted, in women than in men. These folds allow a larger total surface area of brain tissue to be packed into the skull. The surface area of the brain, not its total volume, determines how many neurons and synaptic connections it can store, so these deeply folded areas of the female brain might compensate for the larger overall size of the male brain.

Women have more complex brain tissue in the superior-frontal, parietal, and right inferior-frontal regions. Image courtesy Arthur W. Toga, UCLA.
Eileen Luders and her colleagues in the School of Medicine at the University of California, Los Angeles, created three-dimensional pictures of the brains of 30 women and 30 men, using magnetic resonance imaging (MRI) in combination with a new technique for analyzing the images. The average age of their subjects was about 25 years old. The researchers pinpointed prominent grooves in each brain image to divide the brain into distinct regions. They then looked at the complexity of the cerebral cortex in five different areas: the parietal, occipital, and temporal lobes, and the superior and inferior regions of the frontal lobe.

The researchers found that women had significantly greater cortical complexity than men in the superior-frontal and parietal lobes on both sides of the brain, and in the inferior-frontal lobe in the right hemisphere. No region was more complex in men.

This is the first study to reveal sex differences in the convolutions of the brain. The authors say that the sophisticated three-dimensional imaging analysis they used allowed them to observe these differences. They speculate that cortical folding differences might cause differences in behavior and abilities between women and men. For example, the areas of increased complexity in female brains might be related to cognitive skills in which women usually perform better than men. Or, they might just be females' way of packing equal numbers of neurons into their smaller skulls.

Increased folding in female brains "may help to explain why men and women perform equally in tests of general intelligence," says the study's senior author, Arthur W. Toga, who is a professor in the Laboratory of Neuro Imaging at the UCLA School of Medicine. But it's too early to say if these differences in brain tissue anatomy contribute to behavioral differences, according to Toga. In order to examine this more closely, scientists may have to look at cortical complexity in smaller areas of the brain, because each cortical lobe is responsible for many different behaviors and abilities.

For references and more information, see:
  1. Luders, E., Narr, K.L., Thompson, P.M., Rex, D.E., Jancke, L., Steinmetz, H. and Toga, A.W. Gender differences in cortical complexity, Nature Neuroscience, August 2004, 7(8):799-800. PubMed
  2. She Brains, He Brains - from Neuroscience for Kids
  3. Changing cortical size and shape - from Neuroscience for Kids

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