Edition: U.S. / Global

Men and Women Use Brain Differently, Study Discovers

Published: February 16, 1995

Using a powerful new method for glimpsing the brain in action, researchers have found the first definitive evidence that men and women use their brains differently.

The investigators, who were seeking the basis of reading disorders, asked what areas of the brain were used by normal readers in the first step in the process of sounding out words. To their astonishment, they discovered that men use a minute area in the left side of the brain while women use areas in both sides of the brain.

Dr. Sally E. Shaywitz, a behavioral scientist at the Yale University School of Medicine who was a principal author of the study, said, "As far as I know, this is the first time that anyone has been able to demonstrate anything functionally different" between the brains of men and women.

The new findings follow on a rich body of research looking for sexual differences in the brain. Psychologists have found that women do better on certain tests, like those measuring verbal speed, and that men do better on other tasks, like imagining what an object would look like if it were rotated. Neurologists have found that women seem to recover better from strokes in the left hemisphere of the brain, where language abilities are thought to be situated. Autopsy studies have shown that male brains are more asymmetrical than female brains.

But these previous studies were indirect. The psychological studies could not prove that it was nature, not nurture, that elicited the differences. The anatomical studies could not show what the actual effects of the brain differences were.

The new study, in contrast, showed actual differences in the parts of the brain used when men and women were thinking, and coming up with the same answers.

Dr. Shaywitz said the finding meant that "the brain is a lot more complicated than people envisioned." But it does not say that women's brains are better at this task than men's or vice versa. Although the men and women used their brains differently, she added, the fact that they sounded out words equally well means that "the brain has a lot of different ways to get to the same result."

Dr. Elizabeth Hampson, a neuroscientist at the University of Western Ontario, said the finding "provides definitive evidence" that men and women can use their brains differently to perform the same task. "Nothing was conclusive until now," she said. It means, she said, "we should be open to that possibility in other areas of the brain as well."

Dr. Shaywitz said she was particularly surprised to see differences between men and women in decoding words. Reading, she said, has nothing to do with basic survival skills or reproduction, for which men and women might have developed different brain functions during the long course of evolution. "This is a difference that involves cognition," she said. "And it is the most complex of human functions. Reading is the pinnacle of what humans can do."

Dr. Reid Lyon, director of extramural research on language disorders and learning disabilities at the National Institute of Child Health and Human Development, said the discovery went far beyond a mere curiosity. It is a huge step in a comprehensive research program that is allowing scientists to understand why some children and adults have such difficulty learning to read and it has immediate implications for tests for reading disabilities and strategies to overcome them, he said.

It also might explain why it is that although girls and boys are equally likely to have difficulty learning to read, women seem to compensate better than men for their disability, he said.

Dr. Shaywitz, her husband, Dr. Bennett A. Shaywitz, a neurologist, and their colleagues are publishing their findings today in the journal Nature.

The Shaywitzes' main interest has been to understand the neurological underpinnings of reading disorders. In recent years, they and others have discovered that dyslexia, a difficulty in learning to read, is not a visual problem, not a problem that involves reversing letters, but is instead a language problem. People with reading disabilities have great difficulty breaking words into their most basic units, phonemes. A test for an ability to separate words into phonemes might be to ask a person to say philosophy without the "la" sound or Germany without the "ma."

Dr. Bennett Shaywitz explained that "by convention, we have adopted rules that say that certain sounds in print correspond to certain letters and certain letters form phonemes. The trick in reading is to get from print into phonemes, then it's automatic."

In studying people with reading disabilities who nonetheless learned to read, Dr. Sally Shaywitz said she and others found that they learned to compensate for their inability to decode words into phonemes. "They used other higher order cognitive abilities: their vocabulary, their reasoning power," she explained. But, she said, reading was never easy or automatic for these people.

In the last year, researchers discovered a method that can potentially show the brain in action and that is completely harmless to subjects.

The new method, functional magnetic resonance imaging, can show differences between blood carrying oxygen and blood that is depleted of oxygen. An active area of the brain gets fresh supplies of oxygenated blood. The trick to using functional M.R.I.'s is to design thinking experiments carefully so that they will isolate a particular task.

The Shaywitzes and their colleagues asked their subjects, 19 men and 19 women, to recognize whether nonsense words, like "jete" and "lete," rhyme. The only way to know is to sound them out. And the only way to do that is to use phonemes.

All 19 men used a tiny area of the brain, about a centimeter, or less than half an inch, in diameter, near Broca's region, an area in the front of the left side of the brain, at the temple, that is thought to be used in producing speech. Eleven of the 19 women used this region but also used a comparable area on the right side of the brain. The rest of the women used just the left side of the brain.

The next step, now under way, is to see how children and adults with reading disorders use their brains. The Shaywitzes, who will not comment yet on what they are finding, hinted that those with reading disabilities had profoundly different functional M.R.I. patterns.

Soon, Dr. Lyon said, it should be possible to design simple tests that will reliably detect young children who will have reading disabilities before they are faced with the daunting task of learning to read. It may also be possible to design ways to help these children overcome or even avoid the coming struggle.

Shirley Kramer, executive director of the National Center for Learning Disabilities, an advocacy group based in New York, said she could hardly wait. The new work, she said, "has moved this field forward by leaps and bounds," adding, "There is a real momentum going now."

Photo: Magnetic resonance images of a man's brain, left, and a woman's brain show differences between the sexes in the decoding of words. Men use a small area on one side of the brain, whereas women use areas on both sides of the brain. The lighted spots along the upper right side of the image on the left show a man's brain in action. The image of the woman's brain shows activity on upper right and upper left. (pg. A22)