April 9, 2008

Language and Culture Play Role in Dyslexia

Chinese scientists reported results of a study that found dyslexia affects different parts of the brain in children, depending on whether they learned to read English or Chinese.

The findings could have implications for treatment of dyslexic children, and suggest that therapists may need to use different methods to assist those 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 Li-Hai Tan, the study's lead author and 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," Tan told the Associated Press.

Reading English, an alphabetic language, requires different skills than reading Chinese, which associates symbols with words and relies less on sound representation.

Dyslexia, a language-based learning disability that can involve problems in reading, writing, spelling and speaking words, affects millions of children around the world. Although there is no consensus on the precise number because not all children are screened, the International Dyslexia Association estimates that 8 percent to 15 percent of students are affected.

Tan explained that although previous studies had found the brain may use different neural networks for different languages, none had found a difference in the structural parts of the brain involved.

Using functional magnetic resonance imaging (fMRI), Tan and his team studied the brains of students raised reading Chinese, then compared those findings with similar studies of the brains of students raised reading English.

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

"Becoming a reader is a fairly dramatic process for the brain," Eden, who was not part of Tan's research team on this paper, told the Associated Press.

Learning to read is culturally significant in children, but is not really natural, Eden said. So when the brain adjusts to different writing systems it copes with it differently.

Eden said English-speaking children, for example, learn the sounds of letters and how to combine them into words, while Chinese children memorize hundreds of symbols that represent words.

"The implication here is that when we see a reading disability, we see it in different parts of the brain depending on the writing system that the child is born into," Eden said.

That means, "we cannot just assume that any dyslexic child is going to be helped by the same kind of intervention," she said during a telephone interview with the Associated Press.

The study's findings suggest that treating Chinese speakers with dyslexia may involve working with memory tasks and tests that involve sensor-motor skills, while current treatments of English dyslexia focus on sound awareness and letter-sound conversions, Tan said, adding that the underlying cause of dyslexia remains unknown.

"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 e-mail interview with the AP.

"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.

The researchers said that imaging studies of the brains of dyslexic children using alphabetic languages like English found unusual function and structure in the left temporo-parietal areas, the left middle-superior temporal cortex, and the left inferior temporo-occipital gyrus. These areas are believed to be involved in letter-to-sound conversions in reading, speech sound analysis, and quick word-form recognition, respectively.

In contrast, when the team performed similar imaging studies on dyslexic Chinese children, they found disruption in a different area -- the left middle frontal gyrus region.

In a previous study published two years ago, scientists at the University of Michigan found that North Americans and Asians view the world differently. Participants in the study were shown a photograph, and the researchers found that North American students of European background paid more attention to the object in the foreground of a scene, while students from China spent more time studying the background and taking in the whole scene.

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


On the Net:

A report about the study was published in Monday's online edition of Proceedings of the National Academy of Sciences. A summary of the report can be viewed at http://www.pnas.org/cgi/content/abstract/105/14/5561.

University of Hong Kong

International Dyslexia Association

Georgetown University

University of Michigan

Associated Press