Images of brains of dyslexics show disruption in key circuit Translating letters into sounds is visible with new technology

March 03, 1998|By Sandy Banisky | Sandy Banisky,SUN NATIONAL STAFF

Split-second images of the brain, taken while it reads, show that dyslexics have a disruption in the circuit that translates letters of the alphabet into the sounds of speech, according to a study released yesterday.

The research shows that dyslexia, a condition that makes reading difficult for otherwise normal individuals, is a neurological problem -- and not the result of laziness or low IQ, said Dr. Sally Shaywitz, the Yale University researcher who led the study.

Until now, she said, such evidence was "elusive."

"It's a hidden disability," Shaywitz said. "If you have a broken arm, you can hold up an X-ray and say, 'Oh, here's the fracture.' Until now, we couldn't demonstrate that with dyslexia."

"We've got real pictures. We can see that something's not working right in the dyslexic brain when it comes to decoding the written word," said J. Thomas Viall, executive director of the Baltimore-based International Dyslexia Association.

'It's real'

Viall said the study shows "dyslexia is not a sight problem, not a hearing problem, not an emotional problem, not an intelligence problem. It's a neurobiological disability. It's based in the brain. It's real."

The mapping of the dyslexic brain may one day help parents and teachers diagnose the condition earlier and develop better methods for teaching dyslexics to read, Shaywitz said.

The study, published today in Proceedings of the National Academy of Sciences, included researchers from Yale and the Haskins Laboratories, both of New Haven, and the University of Texas Medical School in Houston.

The Shaywitz team studied 61 right-handed subjects, 29 of whom were dyslexic readers and 32 who had no reading difficulty.

The researchers used new technology called functional magnetic resonance imaging. Similar to the MRIs that doctors might use to diagnose torn ligaments or a brain tumor, but "souped up with some very smart software," the functional MRIs allow scientists to collect thousands of images of the brain as it works on a specific task.

The researchers already had identified the parts of the brain associated with language and reading. In this study, they asked subjects to identify single letters, select rhyming words and decide whether words belong in the same category.

The tasks put progressively higher demands on the regions of the brain that break words down to the sounds that their letters represent. Dyslexics had more trouble at each step.

"In order to read it, the reader has to appreciate that the word 'bat' is made up of three sounds -- 'buh,' 'ah' and 'tuh' -- and that the letters represent those different sounds," Shaywitz said. "The brain is breaking the word down into its underlying sound units."

But in dyslexics, the regions of the brain associated with vision and language function differently from those of normal brains. The dyslexics had trouble decoding the letters. Researchers described this as "an imperfectly functioning system for segmenting words into their phonological constituents" -- the mapping of letters onto sounds.

A 'neurosignature'

"Function was relatively underactive in the back of the brain, relatively overactive in the front of the brain," Shaywitz said. "We believe this may represent a neurosignature for the dyslexic."

Gordon Sherman, president of the International Dyslexia Association and director of the dyslexia research laboratory at Beth Israel Deaconess Medical Center in Boston, said the study shows that "language pathways are developmentally different" in dyslexics. "They are organized differently."

Researchers know that dyslexic children do better if they are taught with lessons that focus on their difficulties. Reports like the Shaywitz study, scientists say, may lead to the development of even better teaching methods.

"We may not have a cure, but a better way to cope," Viall said.

Shaywitz said early diagnosis, with reading lessons, might even change brain function in children as they are trained to read differently from other children.

Pub Date: 3/03/98

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