Saturday, March 13, 2010

A structural–functional basis for dyslexia in Chinese readers

From the Cover: A structural–functional basis for dyslexia in the cortex of Chinese readers

We are by now aware that Developmental Dyslexia is a neurobiologically based disorder that affects ≈5–17% of school children and is characterised by an impairment in reading skills.

For readers of alphabetic (e.g., English) languages, recent neuroimaging studies (fMRI scans) have demonstrated that dyslexia is associated with weak reading-related activity in left temporoparietal and occipitotemporal regions, and the difference in the activity in this area, may be because of reduced gray matter volume in these areas.

In this research study, they find different structural and functional abnormalities in dyslexic readers of Chinese, a nonalphabetic more graphical language. It has often been said that the Chinese do not experience dyslexia but this is not the case. They may simply experience it in a different way.

In comparison with other developing Chinese children, children with impaired reading in logo-graphic 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, the study found reduced activation in this same left middle frontal gyrus region in Chinese dyslexics, and there was a significant correlation between gray matter volume and activation in the language task in this same area.

By contrast, Chinese children who suffer from dyslexia did not show functional or structural (i.e., volumetric gray matter) differences from other developing children, 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.

The Western child will work extremely hard, using their frontal lobes to interpret and understand letters and words, without having access to the long term word storage area in the back of the brain. This may be because the frontal lobes are unable to transfer letters and word data to the long term storage areas or the areas are unreceptive because they are under-developed or have limited capacity.

The Chinese child has no reliance on the long term letter and word storage area at the back of the brain or accesses it in a different way. Their reliance is in the capacity of their frontal lobes, which may or may not be fully developed or functional.

Future studies may look at a) the message and delivery service between the frontal lobes and the back of the brain, long term storage and b) the ability of the frontal lobes to connect succesfully with other cognitive parts of the brain.

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