Differences in dyslexia

A fascinating article came out in the Science section of The New York Times: Patterns: Dyslexia as Different as Day and Night, by Eric Nagourney. The article is based on an original research piece by Wai Ting Siok, Zhendong Niu, Zhen Jin, Charles A. Perfetti, and Li Hai Tan, who examined the abnormalities in brain activity associated with dyslexia in Chinese speakers (in comparison to better documented examples of the disorder in English speakers).

The basic result is simple, but intriguing, especially in light of some of the other research we’ve discussed on how brain areas linked to language differ, Two languages, one brain and theory of mind:

The report, which appeared last week in The Proceedings of the National Academy of Sciences, found that changes in the brain that may contribute to dyslexia are different for English speakers and Chinese speakers.
The difference may be explained by the fact that English is an alphabetic language, the researchers said. A reader sees a letter and associates it with a sound. Chinese characters, on the other hand, correspond to syllables and require much more memorization.

In English-speaking individuals, dyslexia shows up in neuroimaging studies as weak activity in left occipitotemporal and temporoparietal regions of the brain. The researchers find out, however, that readers of Chinese with dyslexia have a different anomaly in their brain, perhaps due to the difference between alphabetic and ideographic languages. Children with (from the abstract) ‘impaired reading in logographic Chinese exhibited reduced gray matter volume in a left middle frontal gyrus region,’ an area that had already been found to be active in reading and writing Chinese characters. ‘By contrast, Chinese dyslexics did not show functional or structural (i.e., volumetric gray matter) differences from normal subjects in the more posterior brain systems that have been shown to be abnormal in alphabetic-language dyslexics’: the abstract details.


As the researchers write, the structural difference in the brain areas associated with dyslexia in Chinese- and English-readers suggests that they may be two different disorders, even though the effect is very similar in terms of ability. I’m left to wonder if ‘dyslexia’ is similar in Chinese- and English-readers or if, examined closely, the disorder… errr, disorders, might manifest in subtly different ways.

References
Siok, Wai Ting, Zhendong Niu, Zhen Jin, Charles A. Perfetti, and Li Hai Tan. 2008. A structural–functional basis for dyslexia in the cortex of Chinese readers. Proceedings of the National Academy of Sciences 105 (14): 5561-5566 10.1073/pnas.0801750105 (abstract)

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