Women Use More of Brain When Listening, Study Says

TIMES SCIENCE WRITER

Confirming what many women have long suspected, new brain research released Tuesday shows that men give only half a mind to what they hear, listening with just one side of their brains while women use both.

This latest insight into the oldest of humanity's differences--gender--doesn't say who is a better listener. But, using a brain scanning technique called functional magnetic resonance imaging (fMRI), the work does highlight the differences in neural activity between men and women listening to someone read aloud.

Conducted by researchers at the Indiana University School of Medicine, the new study is the latest addition to a growing catalog of research suggesting that the mental divide between the sexes is more complex and more rooted in the fundamental biology of the brain than many scientists had once suspected.

"As scientists, we're figuring out what normal is, and more and more often it seems that normal for men may be different than normal for women," said Indiana radiologist Dr. Micheal Phillips, co-author of the study. "That doesn't mean one is better than the other."

The findings were presented Tuesday at the annual meeting of the Radiological Society of North America in Chicago. The research also has been submitted to the journal Radiology.

Understanding whether differences in mental capacity or intellectual ability can be attributed to gender has long confounded scientists, parents, equal rights activists and educators. To be sure, men's and women's brains are more alike than not, but they are definitely not the same--in size, sense or sensibilities.

Only now, however, are reliable studies of metabolic and structural brain organization offering scientists hard evidence of how men and women may differ mentally, often in ways that buck conventional prejudices.

A growing library of medical scans captures the signs of mental activity in living brains. Men and women show significant differences in certain brain areas that are linked to how people think and experience emotions, mathematical reasoning, spatial relations and perceptual speed--and even sense color and sound. Whatever they are doing, women seem to activate more neurons than men.

Some of those differences appear to evolve throughout a lifetime. The brains of aging men and women have significant structural and functional differences, recent research reveals. Men's brains are larger but are more damaged by the aging process; women's brains seem to work more efficiently and appear to age more successfully.

In the new Indiana study, researchers used the brain scanner to study 10 men and 10 women--all healthy--as they listened to a John Grisham thriller read aloud. The fMRI scanner highlights activity in the brain by measuring high-speed changes in neural blood flow.

The radiologists were hoping to develop a simple test to identify critical language areas in those about to undergo brain surgery, to help surgeons avoid damaging certain areas during an operation. Instead, they found what appears to be yet another telltale difference in neural activity between women and men.

As they listened, a majority of the men showed exclusive activity on the left side of the brain, in the temporal lobe, which is associated with listening and speech. The majority of women showed activity in the temporal lobe on both sides of the brain, although predominantly on the left.

"Our research suggests language processing is different between men and women, but it doesn't necessarily mean performance is going to be different," said Indiana radiologist and co-author Dr. Joseph T. Lurito.

"We don't know if the difference is because of the way we're raised, or if it's hard-wired in the brain. We will never be able to figure that out completely."

The Indiana finding follows an influential 1995 study by Yale University brain researchers Sally and Bennett Shaywitz, who discovered that women appear to draw on both sides of their brains when they read, rhyme or engage in other verbal tasks. In contrast, males draw only on brain regions in the left hemisphere for such activity.

Whatever the biological reason for this difference, it may account for the fact that girls usually speak sooner than boys, learn to read more easily and have fewer learning disorders, several experts suggest. Women often also recover their speech abilities more quickly than men after strokes that damage language areas in the left hemisphere of the brain, suggesting that they can more readily draw on other portions of their brains to compensate.

Some of these gender differences in adults may themselves be no more than the end physical result of powerful social conditioning about sexual roles that begins in infancy. Such conditioning might include encouraging aggression in boys and passive behavior in girls. Throughout development, the neurons that make up the brain are remarkably sensitive to such outside influences, some researchers suggest.

At the same time, the biochemistry of gender itself also influences how many genes are activated or are regulated, altering the course of neural development. Indeed, the human brain begins as an essentially female structure; in males it is then altered by the onrush of the hormone testosterone during early development.

"Men generally are more dependent on one side of their brain than women, but what does it all mean?" said UCLA neurobiologist Roger A. Gorski, who studies sex differences in the brain. "I believe that sex differences do exist in the brain but the full significance of this no one really knows."

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He Heard, She Heard

Research released Tuesday shows that men (top scans) listen with one side of their brains, while women (bottom) use both sides. Radiologists at Indiana University School of Medicine used functional magnetic resonance imaging to take pictures of neural activity as volunteers listened to someone read aloud. Areas of intense neural activity are highlighted in red and yellow.

Source: Indiana University School of Medicine

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The research confirms what many women have been saying for years. A19

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