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Brain & Nervous System Health Center

Brain Defect Underlies Reading Difficulties of Dyslexia

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Feb. 16, 2001 (San Francisco) -- A defect in a single part of the brain may underlie the reading difficulties of dyslexics, but intensive training can help them overcome their problems and allow them to read. The findings, presented Thursday at the annual meeting of the American Association for the Advancement of Science, could help researchers find a better way to diagnose and treat at-risk children before reading problems appear.

For years, no one knew what caused dyslexia, which afflicts 10% of the population. They did know, however, that the difficulties of dyslexics are not caused by a poor education or low intelligence. Studies from the last few years have hinted at a biological cause, says Thomas Zeffiro, MD, PhD. But reading is a complex task performed by several parts of the brain, so no one was sure which part was malfunctioning, he says. Zeffiro is co-director of the Georgetown Center for the Study of Learning at Georgetown University Medical Center in Washington, D.C.

To find out, Zeffiro, Guinevere Eden, DPhil, the other co-director of the Georgetown center, and their colleagues examined the brains of dyslexics and normal subjects using a brain-imaging method called functional magnetic resonance imagining -- a variant of the brain-scanning procedures doctors use to diagnose brain maladies that can detect changes in brain activity.

Although it seems simple, reading is a complex task, says Eden. Readers must see symbols and deduce what they mean, sound out words in their head, and grasp what each sound means. "Children who are good at this succeed in reading," Eden says.

Thirty-seven subjects -- 20 with dyslexia and 17 who read normally -- were monitored as they read and as they tried to detect moving dots on a computer screen. Dyslexics have problems with both tasks. An area of the brain called the left parietal lobe lit up for both tasks in both groups, but it lit up less for dyslexics. That meant that a single brain defect underlies both tasks, pointing to a common brain defect that goes awry in dyslexia.

The work is "further evidence that dyslexia has biological roots," says Eden.

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