S/He-Brains

By Sarah Richardson|Thursday, June 01, 1995
RELATED TAGS: SEX & THE BRAIN, LEARNING
For most kids, learning to read is just a question of practice. But an estimated 20 percent of Americans have persistent trouble converting letters on a page into sounds. Recently a brain-imaging study pinpointed where that seemingly magical conversion takes place. That was an important result: a first step toward untangling the neurological basis of why so many perfectly smart people have trouble learning to read. But what grabbed headlines was the study’s second result: women do it differently from men.

The authors of the study, pediatrician Sally Shaywitz and her husband, neurologist Bennett Shaywitz, weren’t looking for sex differences; as codirectors of the Yale University Center for the Study of Learning and Attention, they’ve been studying reading disabilities for a long time. For their most recent study, though, the Shaywitzes used the most sophisticated new brain-imaging technique available--functional magnetic resonance imaging (fMRI). Like other brain-imaging techniques, fMRI detects tiny shifts in blood flow that indicate which parts of the brain are more active. But fMRI, says Sally Shaywitz, is more precise than other techniques--which is how she and her husband ended up discovering sex differences in phonological processing, or letter-to-sound conversion.

The Shaywitzes studied 19 men and 19 women, all neurologically normal. As the subjects lay in the fMRI scanner, they were tested on four language-related tasks--each requiring them to compare two patterns on a video screen, and each more complex than the last. In the first task, the subjects decided whether two series of lines were going in the same direction. In the second, they decided whether two strings of uppercase and lowercase letters matched in both letter and case. In the third, they decided if two nonsense words--say, slote and roat--rhymed. This task tested the ability to match symbol to sound--the skill that most people with reading disabilities are deficient in. The final task tested understanding: the subjects had to decide, for example, whether the words senator and congressman belong in the same category.

Men and women showed a difference in brain use only on the rhyming task. In both sexes, trying to recognize rhymes led to increased blood flow in the inferior frontal gyrus of the left hemisphere--Broca’s area, as it’s commonly called--which has long been linked to language ability. In men that was the only active region, whereas 11 of the 19 women also showed activation in the corresponding region in the right hemisphere. The women’s brains weren’t working any harder overall; the work was just spread out more. The accuracy was very comparable, Sally Shaywitz says. It may be that there are just different routes in the brain to get to the same results.

Neither the Shaywitzes nor anyone else, though, knows for sure what the difference they detected means. Does it relate in any way to the observation that women are less likely to lose language ability when they suffer left-hemisphere strokes? To the fact that women tend to do better on tests that measure verbal fluency?

The women in the Shaywitz study, it’s worth emphasizing, didn’t do better than the men, they just did differently--and they did differently only on the rhyming task. On the fourth task, which required them to understand the meaning of words, their brains worked the same as the men’s. And even on the rhyming task, only 11 of the women were different from the men; the other 8 were not. So it’s not even clear that the difference in brain use detected by the Shaywitzes is a natural difference between the sexes; conceivably it could result from differences in upbringing.

The truth is, we’re no closer to answering the timeless questions--why men are less likely than women to ask for directions, more likely to vote Republican, and so on. On the other hand, we may be a little bit closer to understanding reading disabilities. Women tend to have more success at overcoming such disabilities--is it because they process letters into sounds on both sides of the brain? Says Shaywitz: We’re going to investigate that possibility.
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