National Post

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Tuesday, April 20, 1999

Women, men do think differently
Neurons V. Synapses

Michael Smith
National Post

Men have more neurons in the part of the brain where thinking occurs, while women have more connections between them, research released today shows.

The finding may help explain some differences in behaviour between males and females, according to Gabrielle de Courten-Myers, associate professor of neuropathology at the University of Cincinnati.

But Courten-Myers cautioned against interpreting the study as evidence that either the male or female brain is superior to the other: "That could cause tremendous harm," she told reporters at the annual meeting of the American Academy of Neurology, being held this week in Toronto. Instead, more neurons may be better for some brain functions, while more connections are better for others.

To collect her data, Courten-Myers painstakingly counted the numbers of neurons in 64 sites in the cerebral cortexes of 10 males and seven females aged six to 31. The subjects were healthy and had died in accidents. (Earlier studies that showed differences between men and women or between racial groups, were criticized because the subjects had died of age or disease, which can change the brain.)

Courten-Myers' results showed that on average males had 13% more neurons than females. But the extra space in the female brain had more synapses, dendrites, and axons that allow neurons to communicate.

The cerebral cortex, the densely folded outer layer of the brain, is responsible for voluntary movement, sensory perception, and functions such as memory, reasoning, learning, and language.

"There was a statistical significance for the morphological [structural] differences," she said. "What it means is much more speculative."

The finding may help explain, she said, why it is that women are more susceptible to some forms of dementia as they age: the impact of losing even a few neurons would be greater on women than men; or why boys are more likely to have learning disabilities: fewer neuron-to-neuron connections.

Canadian neuroscientist Sandra Witelson, of McMaster University in Hamilton, Ont., said the results were surprising. In a landmark study published in 1995 "we reported the exact opposite."

Witelson, one of the world's leading researchers on sex differences in the brain, said her 1995 study arose because she was interested in whether there were sex differences in the temporal lobes of the brain, where speech and related functions are located.

She found that women had 11% or 12% more neurons than men. "But of the six layers in the cerebral cortex, only two showed sex differences," she said.

The new study does not negate the earlier research. Courten-Myers sampled the whole brain, while Witelson's study was restricted to one area. It is possible that both reports are correct, said Witelson. "The truth will come out sooner or later," she said.

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