Researchers are reporting direct neurological evidence that the region of the brain that processes brief, rapidly successive sounds is functionally abnormal in adults with the reading disability known as dyslexia. The findings, documented through simultaneous brain imaging and behavioral tests, strongly indicate, the researchers said, that adult dyslexics have an enduring neurological deficit in their ability to process these brief, rapidly successive sounds.
They suspect that the deficiency contributes to difficulties in early speech and language learning, and leads to a weakness in the subsequent mental leap in abstraction to words on a page that enables people to learn to read. The study was published in the May 24 issue of Proceedings of the National Academy of Science.
Perhaps the most provocative aspect of the finding, the researchers said, is the clear and direct neurological evidence that reading deficits are generated, at least in part, by a deficit at a very fundamental level of cortical processing of sound inputs.
"Our findings indicate that there is a basic problem in signal reception, as complex sound information streams into the cerebral cortical system underlying aural speech representation," said the senior author of the study, Michael Merzenich, Ph.D., the Francis A. Sooy Professor of Otolaryngology and a member of the Keck Center for Integrative Neuroscience at UC San Francisco. "The way that the brain processes sound in poor readers is very different from its processing and representation of rapidly changing sound inputs in competent readers."
"Our research indicates that adult dyslexics are representing the sound parts of
words by the activation of cortical neuron populations in a weaker and less
salient form within their cortical aural speech processing system. We believe
that they, therefore, are not delivering the normal forms of representation of
the separable sound parts of words to the regions of the brain involved in
Contact: Jennifer O'Brien
University of California - San Francisco