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Dyslexia Affects Hearing Process

Left Brain Activity Differs from Nonimpaired Readers
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WebMD Health News

Oct. 27, 2003 -- It is becoming increasingly evident that people with dyslexia process sound and language differently from people who don't have trouble reading.

Using a highly precise imaging technique, University of Texas researchers compared brain activity in areas known to be associated with analyzing the sound structure of written and spoken words in children with dyslexia with children without reading problems. They found that the areas of the left-brain associated with speech were highly active in the nonimpaired readers and not very active at all in those who were dyslexic.

The findings are consistent with the idea that problems understanding the "sound structure" of both written and spoken language are associated with abnormal activity in this area of the brain, the researchers say.

"We are not the only ones to find that this neurological deficit appears to be confined to very restricted areas of the brain," researcher Joshua Breier, PhD, tells WebMD. "The evidence is overwhelming that dyslexia is a very specific learning disability, and not a problem with intellect."

Left Brain, Right Brain

In this study, 12 children with dyslexia and 11 nonimpaired children were given simple speech-perception tests. Brain activity was simultaneously observed using a noninvasive imaging technique known as magnetoencephalography (MEG). The findings are reported in the October issue of the American Psychological Association journal Neuropsychology.

When the nonimpaired readers were distinguishing between sounds, they showed more activity in the left part of the brain associated with sound and speech. The children with dyslexia showed little activity in the area, but after a time showed more activity in the corresponding, but functionally mysterious, areas on the right side of the brain. The poorer the performance on the speech-perception tests, the more the right side of the brain "lit up" during testing.

In earlier studies the researchers found similar patterns of brain activity in dyslexic and nonimpaired children tested while they were reading.

Breier tells WebMD that it is not yet clear whether the right-sided brain activity seen in children with dyslexia occurs as an attempt to compensate for the left-brain inactivity, but other recent studies do show that this is the case.

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