Women are more emotional. Men are more rational. Men are better at math, women at English. Men are insensitve. Women are nurturing.
Gender stereotypes like these have persisted for centuries, contributing to the popular notion that men and women view the world in fundamentally different ways. Although most of these ideas are completely unfounded, a substantial body of scientific research has demonstrated that there are anatomical differences between the brains of men and women. The research has now gone a step further - a husband-and-wife team of Yale researchers has published a study showing that the brains of men and women are not only structured differently, but function differently as well.
The study, which was published in the Feb. 16 issue of Nature, was done by Drs. Bennet and Sally Shaywitz, co-directors of the Yale Center for Learning and Attention at the Yale School of Medicine. Using a new technique that produces computerized images of the active areas of the brain, they proved that while performing specific tasks involving language, men use only one side of the brain while women use both.
This is the first time that researchers have identified differences in male and female brain function, though anatomical differences in the brain have been known for some time.
The Shaywitzes' research primarily focuses on learning disorders, and in this experiment, they performed a series of tests on the way people process language. Although the brains of men and women behaved in essentially the same way with tasks involving letter recognition and category choices, there was a sharp gender difference in a task involving rhyming. Nineteen men and 19 women were asked to rhyme nonsense words, such as "lete" and "zete." Using nonsense words forces subjects to sound out words, rather than rely on other means, such as merely recognizing a familiar word visually, according to Sally Shaywitz.
Both men and women used the inferior frontal gyrus, a small area near Broca's region, a part of the brain which has long been associated with speech. The researchers discovered brain activity only in the left hemisphere of the men's brains. The majority of women studied, however, used both the left and right inferior frontal gyrus of their brain. This difference indicates that women use both sides of their brains while brain activity in males tends to be more asymmetrical.
The findings could have immediate implications for learning and testing, and could shed light on why girls with reading disorders seem to fare better as adults than boys do, according to Sally Shaywitz. Also, there is some evidence that women recover better from strokes, which is perhaps related to the ability to use both sides of the brain, she said.
The researchers used what Sally Shaywitz called "the wonderful new technology" of functional magnetic resonance imaging (fMRI), which allowed them to take computerized images of the working brain. This technology allows scientists to take "the first step in relating brain function to cognitive function," Sally Shaywitz said. Developed by another Yale researcher, John Gore, professor of diagnostic radiology and director of nuclear magnetic resonance) research, fMRI uses the blood's magnetic properties to show what regions of the brain are being used when the subjects perform specific tasks. A strong magnetic field is passed through the brain; when an area of the brain is active, its blood flow increases, highlighting it on the MRI screen.
Sally Shaywitz said that they now plan to use fMRI for testing people with learning disorders. The technique will identify differences in the way that they process language. The Shaywitzes are currently studying learning-disabled women and will compare the results to those of the normal women already studied.
This study continues a substantial body of research that examines the differences between the brains of men and women; several studies indicate that parts of the corpus collosum (connective tissue between the two hemispheres of the brain) is larger in women's brains than in men's, indicating that women are more likely to use both sides, while men's brains are more asymmetrical.
"People have long suspected that men's brains are more lateralized than women's, but this is the first proof that there are functional differences," Sally Shaywitz said.
She added that people should not read too much into the study, but said that it shows that the brain is much more complicated than people realize. "What was especially interesting was that although men's and women's brains functioned differently, their comparable ability was very similar, indicating that there are potentially many diffferent ways that the brain performs the same task."
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