Studies discover brain abnormality that may be cause of dyslexia

August 16, 1994|By Newsday

New studies of brain tissues have led to the discovery of a structural abnormality that may be the cause of dyslexia, doctors reported yesterday.

Three researchers in Boston have found a significant difference between dyslexic persons and non-dyslexics in the size of their nerve cells in the part of the brain that helps process sounds -- the left MGN, or left medial geniculate nucleus.

While it was long suspected that dyslexia is a visual problem -- causing trouble with reading and writing -- recent research suggests that it instead stems mostly from words not being heard and learned properly.

The size difference in the neurons of dyslexic persons -- more small neurons and fewer big neurons, compared with normal persons -- might be what hampers information processing. Having too few large neurons could make it difficult for dyslexics to follow rapidly changing sounds, especially the word sounds in human speech.

"This is consistent with their inability to process certain sound combinations," said neurologist Dr. Albert Galaburda, the leader of the research team. Rapid sound processing "is essential for learning language and learning to read easily."

The mismatch in the ratio of large to small neurons in the left MGN was found during the dissection of brain tissues from five dyslexic persons and comparisons with tissues from seven non-dyslexics.

Neurobiologist Margaret Livingstone at Harvard Medical School said Dr. Galaburda's results are not conclusive because of the small number of people studied, but that "this is one of those cases where one should publish a very inconclusive result. It may encourage more dyslexics to will their brains to science" so the research can be expanded.

Dyslexia is relatively common, afflicting about 12 million Americans. It is an inborn problem that involves difficulty in language learning, reading and writing. Dyslexics are usually of average, or higher than average, intelligence.

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