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.

And it is important because it shows that "dyslexia is not an auditory problem and not a visual problem -- it's a problem with the auditory-visual connection," says Frank Wood, PhD, chief of neuropsychiatry at Wake Forest University School of Medicine in Winston-Salem, N.C.

To see if those biological problems can be overcome, Eden and her colleagues did brain scans on 20 dyslexic adults, then put 10 of them on an intensive training program. The program, which was designed to improve reading skills, consisted of three hours per day of training for eight weeks.

The 10 dyslexics who received the training learned to read, even forming a book club at the end of the training period. What's more, they compensated for the weak performance of their left parietal lobe by learning to use their right parietal lobe. According to Eden, the results show that the adult brain is capable of change. "It says you shouldn't give up on adult dyslexics," she says.

Knowing a biological cause for dyslexia should help researchers come up with better ways of diagnosing the disorder. Currently, most children are not diagnosed as dyslexics until they are in the second or third grade and have a hard time reading. "As a society, we're not doing a very good job at diagnosing children at risk for reading failure," Zeffiro says.

But understanding the specific brain functions and regions that go awry should allow researchers to come up with better diagnostic tests for children as young as 4 or 5. Those at-risk children could be directed to an intervention program that would help them learn to read better, Zeffiro says.

Parents should be aware that young children are at risk of dyslexia if at least one parent or relative has it, says Wood. And they should also be wary of quick and easy fixes for dyslexia. "Dyslexia can only be treated by trained teachers," he says.