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In an international study published this week by the prestigious international scientific journal Nature, they have found that dyslexia, rather than being caused by a universal deficit in the brain that is common to all languages, is instead associated with specific brain abnormalities that are shaped by the characteristics of the native language and culture.
Through a pioneering series of brain-imaging studies, they have shown, for the first time, that the abnormal pattern of activity seen in the brains of dyslexic individuals is not the same in Chinese children as it is in others.
Dyslexia, a common reading and language disorder, affects 5 to 10 percent of alphabetic language speakers. It is also a common disorder in Chinese communities. Experts estimate that approximately 2 to 7% of Chinese children are affected by developmental dyslexia. These children have severe problems with reading that are not accountable by any kind of deficit in general intelligence, educational opportunity, and motivational factors. If not treated effectively, dyslexia can have a profound negative effect on a child's educational attainment and quality of life.
The HKU researchers used functional magnetic resonance imaging (fMRI) to scan Chinese dyslexic children's brain activity while they were reading. In a character sound decision task, poor Chinese readers showed a reduced activation of the left middle frontal cortex compared to normal readers. In a second task, called a "lexical decision" task, which tapped the association between visual shapes of the characters and their meaning, weaker activation was also seen in the left middle frontal cortex for Chinese dyslexics. Moreover, dyslexics showed stronger activity in the part of the brain responsible for visual analysis of Chinese characters.
Dr Tan Li-Hai is associate professor of the Department of Linguistics at the University of Hong Kong and was the research fellow of the National Institute of Mental Health (NIMH) Intramural Research Programme. "Previous research using alphabetic languages found that dyslexic children show a reduced activity in the left temporoparietal part of the brain compared to good readers," he said. The left temporoparietal areas are traditionally associated with decoding written materials.
"Dyslexic children have problems in using letter-to-sound conversion rules and are less sensitive to sound structures of spoken words, so phonological deficits are a core cause of dyslexia in alphabetic languages." In contrast, what Tan and his colleagues found was that Chinese dyslexic children differed in that they do not show activity in the left temporoparietal area of the brain. It shows therefore that this particular area is not associated with dyslexia per se, but only with dyslexia in readers of alphabetic languages.
"English follows letter-to-sound conversion rules, whereas written Chinese is a logographic system that maps visual shapes onto meanings," said Dr Siok Wai-Ting, lead author of the study and assistant research professor of linguistics at the University of Hong Kong.
Because the relation between visual form and pronunciation is arbitrary in Chinese, children learn the characters' visual form, sound information and meaning by rote. Reading difficulty in Chinese develops not only from the poor quality of the links between the characters' visual shape and their pronunciation, but also from a substandard connection between visual shape and meaning. Both deficits appear to be caused by the weaker activation found in the left middle frontal gyrus.
The overactivation of the right occipital cortex in Chinese dyslexics, on the other hand, indicates that poor readers struggle even in the visual spatial analysis of characters.
The research was supported by a HKSAR Government Central Allocation Grant disbursed by the Research Grants Council of the University Grants Committee of Hong Kong and by funding from the NIMH.
For further enquiries, please contact Dr Li-Hai Tan or Dr Siok Wai-Ting of HKU's Department of Linguistics (e-mail: tanlh@hku.hk, siok@hku.hk or tel: 2241 5890, 2241 5877) or Miss Polo Leung of HKU's External Relations Office at 2859 2600.
Biological Basis of Dyslexia Dependent on Culture according to HKU Researchers
31 Aug 2004
Researchers from The University of Hong Kong, in collaboration with colleagues at the University of Pittsburgh and the Beijing 306 Hospital, report findings that challenge current views about the biological basis for dyslexia.
In an international study published this week by the prestigious international scientific journal Nature, they have found that dyslexia, rather than being caused by a universal deficit in the brain that is common to all languages, is instead associated with specific brain abnormalities that are shaped by the characteristics of the native language and culture.
Through a pioneering series of brain-imaging studies, they have shown, for the first time, that the abnormal pattern of activity seen in the brains of dyslexic individuals is not the same in Chinese children as it is in others.
Dyslexia, a common reading and language disorder, affects 5 to 10 percent of alphabetic language speakers. It is also a common disorder in Chinese communities. Experts estimate that approximately 2 to 7% of Chinese children are affected by developmental dyslexia. These children have severe problems with reading that are not accountable by any kind of deficit in general intelligence, educational opportunity, and motivational factors. If not treated effectively, dyslexia can have a profound negative effect on a child's educational attainment and quality of life.
The HKU researchers used functional magnetic resonance imaging (fMRI) to scan Chinese dyslexic children's brain activity while they were reading. In a character sound decision task, poor Chinese readers showed a reduced activation of the left middle frontal cortex compared to normal readers. In a second task, called a "lexical decision" task, which tapped the association between visual shapes of the characters and their meaning, weaker activation was also seen in the left middle frontal cortex for Chinese dyslexics. Moreover, dyslexics showed stronger activity in the part of the brain responsible for visual analysis of Chinese characters.
Dr Tan Li-Hai is associate professor of the Department of Linguistics at the University of Hong Kong and was the research fellow of the National Institute of Mental Health (NIMH) Intramural Research Programme. "Previous research using alphabetic languages found that dyslexic children show a reduced activity in the left temporoparietal part of the brain compared to good readers," he said. The left temporoparietal areas are traditionally associated with decoding written materials.
"Dyslexic children have problems in using letter-to-sound conversion rules and are less sensitive to sound structures of spoken words, so phonological deficits are a core cause of dyslexia in alphabetic languages." In contrast, what Tan and his colleagues found was that Chinese dyslexic children differed in that they do not show activity in the left temporoparietal area of the brain. It shows therefore that this particular area is not associated with dyslexia per se, but only with dyslexia in readers of alphabetic languages.
"English follows letter-to-sound conversion rules, whereas written Chinese is a logographic system that maps visual shapes onto meanings," said Dr Siok Wai-Ting, lead author of the study and assistant research professor of linguistics at the University of Hong Kong.
Because the relation between visual form and pronunciation is arbitrary in Chinese, children learn the characters' visual form, sound information and meaning by rote. Reading difficulty in Chinese develops not only from the poor quality of the links between the characters' visual shape and their pronunciation, but also from a substandard connection between visual shape and meaning. Both deficits appear to be caused by the weaker activation found in the left middle frontal gyrus.
The overactivation of the right occipital cortex in Chinese dyslexics, on the other hand, indicates that poor readers struggle even in the visual spatial analysis of characters.
The research was supported by a HKSAR Government Central Allocation Grant disbursed by the Research Grants Council of the University Grants Committee of Hong Kong and by funding from the NIMH.
For further enquiries, please contact Dr Li-Hai Tan or Dr Siok Wai-Ting of HKU's Department of Linguistics (e-mail: tanlh@hku.hk, siok@hku.hk or tel: 2241 5890, 2241 5877) or Miss Polo Leung of HKU's External Relations Office at 2859 2600.
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