Study: Dyslexia Differs by Language

Dyslexia affects different parts of children’s brains depending on whether they are raised reading English or Chinese. That finding, reported in Monday’s online edition of Proceedings of the National Academy of Sciences, means that therapists may need to seek different methods of assisting dyslexic children from different cultures.

“This finding was very surprising to us. We had not ever thought that dyslexics’ brains are different for children who read in English and Chinese,” said lead author Li-Hai Tan, a professor of linguistics and brain and cognitive sciences at the University of Hong Kong. “Our finding yields neurobiological clues to the cause of dyslexia.”

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Reading an alphabetic language like English requires different skills than reading Chinese, which relies less on sound representation, instead using symbols to represent words.

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Tan’s research group studied the brains of students raised reading Chinese, using functional magnetic resonance imaging. They then compared those findings with similar studies of the brains of students raised reading English.

Guinevere F. Eden, director of the Center for the Study of Learning at Georgetown University in Washington, said the process of becoming a skilled reader changes the brain.

“Becoming a reader is a fairly dramatic process for the brain,” explained Eden, who was not part of Tan’s research team on this paper.

For children, learning to read is culturally important but is not really natural, Eden said, so when the brain orients toward a different writing system it copes with it differently.

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That means, “we cannot just assume that any dyslexic child is going to be helped by the same kind of intervention,” she said in a telephone interview.

Tan said the new findings suggest that treating Chinese speakers with dyslexia may use working memory tasks and tests relating to sensor-motor skills, while current treatments of English dyslexia focus on letter-sound conversions and sound awareness.

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“Previous genetic studies suggest that malformations of brain development are associated with mutations of several genes and that developmental dyslexia has a genetic basis,” he said in an interview via e-mail.

“We speculate that different genes may be involved in dyslexia in Chinese and English readers. In this respect, our brain-mapping findings can assist in the search for candidate genes that cause dyslexia,” Tan said.

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The study was funded by the Ministry of Science and Technology of China, the Hong Kong Research Grants Council and the University of Hong Kong.

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[Editor’s Note: “Functional and Morphometric Brain Dissociation Between Dyslexia and Reading Ability,” by Fumiko Hoeft et al. can be read on-line here. It can be downloaded as a PDF document here.