Biology of Dyslexia Varies With Culture, Study Finds

[Harold F. Schiffman]

NYTimes,  September 7, 2004
http://www.nytimes.com/2004/09/07/science/07read.html

Biology of Dyslexia Varies With Culture, Study Finds
By ANAHAD O'CONNOR

Reading may be a uniquely human talent, but it is not an innate skill.
Writing systems differ vastly from one culture to the next. Chinese, for
example, is composed of thousands of logographic symbols, while English
has a mere 26 alphabetical building blocks. A new study suggests that the
biology underlying reading disorders may also vary by culture. Chinese
speakers who suffer from dyslexia, the study found, have different brain
abnormalities than English speakers who are dyslexic. The report was
published last week in the journal Nature.

The results suggest that the treatments for English speakers with dyslexia
might not be effective for those who speak other languages and have the
disability. "Until now, the main theory in the literature was that
dyslexia in all languages would have a single universal biological
origin," said Dr.  Li-Hai Tan, a research fellow at the National Institute
of Mental Health and an author of the study. "But the Chinese language is
so different from English and other alphabetical languages that we assumed
that the neurobiological basis could not be the same."

Dyslexia affects up to 15 percent of Americans, and about 7 percent of
people in China. Most brain imaging studies of children with the disorder
have identified anomalies in the left temporoparietal region of the brain,
an area that helps attribute blocks of sound - called phonemes - to
different letters and decodes their meaning. But those studies looked only
at dyslexics who spoke alphabet-based languages, like English, German and
French. Learning to speak Chinese is a different mental task, Dr. Tan
said, requiring the memorization of about 5,000 to 6,000 characters, each
corresponding to a different word. As a result, dyslexic Chinese speakers
have trouble converting symbols into meanings, not letters into sounds.

"If you think about Chinese, it requires much more visual processing than
English, which relies more on stringing sounds together," said Dr.
Guinevere Eden, director of the Center for the Study of Learning at
Georgetown University, who was not involved in the study. "In English, we
learn that words are made up of chunks and that you can come across a word
you've never seen before and apply the rules. That doesn't work in
Chinese; you really have to memorize the characters to master the
language." In an earlier study, Dr. Tan found differences in patterns of
brain activity between normal Chinese readers and English readers.
Speculating that the contrasts might hold for learning disorders as well,
Dr. Tan, in research carried out at the University of Hong Kong, did brain
scans on 16 children as they studied Chinese characters on a screen. Half
of the subjects were normal readers, the other eight were dyslexic.

In one task, they had to decide whether two different characters had the
same pronunciation. In a second test, they were shown real and fake
characters and asked about their meanings. Both groups had normal activity
in the left temporoparietal cortex. But the dyslexic children showed
glitches in a separate region, the left middle frontal gyrus, which helps
coordinate shape, meaning and pronunciation.

The findings suggest that a person can be dyslexic in one language but not
in another. At least one case study supports that: In 1999, researchers
found that a boy with dyslexia in English had no problems reading in
Japanese. Dr. Tan, however, has found evidence that bilingual speakers use
one brain region for different languages. He showed that Chinese speakers
who learn English use the left middle frontal cortex - not the left
temporoparietal cortex, which native English speakers use. Based on this,
he said, a person who is dyslexic in Chinese should also have difficulty
reading in English, but it is too soon to tell.

"What we know is that dyslexics tend to be quite a heterogeneous group,"
Dr. Eden said. "With English dyslexics, the areas of the brain affected
are multiple. And with Chinese, we're probably looking at several
different areas that are affected as well."


http://www.nytimes.com/2004/09/07/science/07read.html