Men and women really do use their brains differently, study confirms

January 27, 1995|By Knight-Ridder Newspapers

PHILADELPHIA -- Brain researchers at the University of Pennsylvania have uncovered strong evidence of what everybody already knows.

In some important respects, men and women don't think alike. They literally use their brains differently.

A study of brain use patterns in 61 Philadelphia-area subjects reported in the current issue of Science found a biological basis for long-noted behavioral differences between the sexes -- differences such as the fact that, for instance, men are far more prone to violence than women, or the fact that women tend to have a harder time with math.

"Our findings do not answer the question of whether the differences are genetic or cultural in origin," said Ruben C. Gur, the Penn neuropsychologist who wrote the report. "After all, culture shapes the brain just as the brain shapes culture. I can tell you which came first if you can tell me if the chicken came before the egg."

The evidence suggests that, on average, women are more inclined to exercise a portion of the lower brain that helps refine the way emotions are expressed, and are also more likely than men to flex the side of the brain associated with abstract thinking, verbal memory and flexible problem-solving.

Men, on the other hand, think like lizards. Also, they tend to be better at algebra and trig. But let Dr. Gur explain:

"If you peel off the outer cortex you get to the part of the brain we share with reptiles and beasts of prey, the limbic system. It is made up of several structures, some older and more primitive than others. The most complex portion of the limbic system is the singulate gyrus, which is thought to be involved in regulating emotion." The study concludes that women tend to use the singulate gyrus more than men do.

In the case of aggression, this more recently evolved portion of the limbic system seems to afford a broader range of emotional options. A chimpanzee can do more with aggression than, say, an alligator. Rile a gator and he's got one attack mode -- hard and fast, with his teeth forward. An angry chimp, on the other hand, can opt for something short of frontal assault. He can try, for instance, to scare away an enemy by baring his teeth or making threatening noises or gestures.

"The lower, older portion of the limbic system is what we share with reptiles," explained Dr. Gur, who directs Penn's Brain Behavior Laboratory. "The singulate gyrus isn't there with reptiles. You do see it in apes and in man."

Each of the 61 subjects (37 men and 24 women), who answered ads, were injected with a slightly radioactive glucose solution. Proton Emission Tomography (PET) scans were then used to observe how their brains took up the glucose -- the brain feeds off of sugar in the blood. The more active portions of the brain absorb the most glucose.

Computers display the glucose uptake in the form of colorful brain images. Researchers can actually observe what portions of the brain are active or at rest. By comparing the images, they can observe even slight differences between subjects' brains in action.

For the most part, the PET scans were "remarkably similar" for men and women, Dr. Gur said. The anatomy of the male and female brains were the same; the only differences came in a small number of functions. The biggest difference was in the limbic system. Women tended to have a far more active singulate gyrus than men, who displayed much more activity in the lower, more primitive limbic regions.

"If the singulate gyrus is responsible for modulating emotional response, it might help explain why women are far less likely than men to express emotion aggressively, or violently," said Dr. Gur.

More activity in the singulate gyrus might also reflect the tendency of women to be more finely sensitive than men at reading emotional cues. Studies have shown that women are more adept than men at interpreting facial expressions. Said Dr. Gur, "Men are very good at reading happiness on a woman's face, but often miss signs of sadness altogether."

More subtle observations reflected other well-documented differences between the sexes. Brain studies have long shown that (for right-handed people) the left hemisphere of the brain is most active in verbal and analytical tasks, while the right hemisphere controls spatial problem-solving. All of the subjects in the study were right-handed.

Dr. Gur and his associates found that women tended to have more active left hemispheres, which would correspond with the superior verbal memory talents of women.

"It has long been known that if you give men and women a list of words to memorize, on average, women will remember more of the words than the men," Dr. Gur said.

On the other hand, men routinely score higher than women on math tests and other measures of spatial problem-solving, or right-brain tasks.

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