Thursday, April 17, 2008

Brain changes in dyslexia - different in Hong Kong and Chicago

Siok et al show that the brain changes associated with dyslexia in an alphabetic versus an ideographic language can be different. In alphabetic language, a reader sees a letter and associates it with a sound. Chinese characters correspond to syllables and require much more memorization. Both Chinese and English dyslexics find it harder to make their way through even fairly simple written material. This study suggests that their brain mechanics as they try to read may be as different as Chinese is from English. Here is their abstract:

Developmental dyslexia is a neurobiologically based disorder that affects approximately 5–17% of school children and is characterized by a severe impairment in reading skill acquisition. For readers of alphabetic (e.g., English) languages, recent neuroimaging studies have demonstrated that dyslexia is associated with weak reading-related activity in left temporoparietal and occipitotemporal regions, and this activity difference may reflect reductions in gray matter volume in these areas. Here, we find different structural and functional abnormalities in dyslexic readers of Chinese, a nonalphabetic language. Compared with normally developing controls, children with impaired reading in logographic Chinese exhibited reduced gray matter volume in a left middle frontal gyrus region previously shown to be important for Chinese reading and writing. Using functional MRI to study language-related activation of cortical regions in dyslexics, we found reduced activation in this same left middle frontal gyrus region in Chinese dyslexics versus controls, and there was a significant correlation between gray matter volume and activation in the language task in this same area. 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 results suggest that the structural and functional basis for dyslexia varies between alphabetic and nonalphabetic languages.

3 comments:

John Hayes said...

All observations and evidence about dyslexia suggest that there is not a single cause for dyslexia. Different dyslexics have different problems as related to reading at least in English.
Chinese dyslexia problems are concentrated in the visual processing centers because in their written language images need to be learned rather that sounds of letters.

Only by beliving that dyslexia has one cause and is a single condition can the researchers say Chinese and English readers are different. That is not true. The genetic research that has found genes associated with dyslexia are studies of particular families with a high incidence of dyslexia. There is little evidence of widely spread genetic influences.

If two families can have different dyslexia genes and yet both families are dyslexic and express their dyslexia in different ways it is hard to argue the single cause od dyslexia position. All the fMRI studies conclude that they can see differences between groups of dyslexics and non dyslexics but can not identify individuals as dyslexic or not.

It is not that English dyslexics don't have visual processing problems. It is that people with visual processing problems that are Chnese are concentrated into the dyslexic population because of the need for visual processing is more important to reading Chinese.

I suggest that English reading dyslexics have about a 25% incidence of visual image processing problems.

The incidence of Chinese having dyslexia is about 25% of the incidence of English dyslexics .

I suggest that the incidence of visual imaging processing problems that cause reading problems is the same in both English and Chinese general populations.

The higher rate of reading problems in English readers is due to having additional tasks to read each task can cause different problems that do not show up in China because different skills are needed to learn Chinese.

I see See Right Dyslexia Glasses that remove the problems of visual dyslexia at www.dyslexiaglasses.com and about 25% of English dyslexics can describe visual problems that make reading difficult.

Dyslexia is not caused by a single factor. It is a syndrome that affects different dyslexics differently.

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