Developmental dyslexia is a disorder affecting as many as 17% of school children. This neurological disorder involves an impairment in reading skills, and has been found to be “associated with weak reading-related activity in left temporoparietal and occipitotemporal regions” in English speakers. However, different abnormalities in the brain are associated with dyslexic readers in the non-alphabetic Chinese language, according to research just published in the Proceedings of the National Academy of Sciences.
This is not terribly surprising. Earlier research had shown that individuals with linguistic abilities in both English and Chinese who later suffer brain damage (such as a stroke) may have aphaisa (inability to produce or comprehend language) in relation to one language but not the other. Furthermore, non-alphabetic languages seem to recruit different brain areas than alphabetic languages for processing of the written form.
Figure 1 from the paper: Group differences in gray matter volume. (a, b, and d) A region in the left middle frontal gyrus (BA 9; x = -32, y = 31, z = 28) exhibited reduced volume in the dyslexic group, P < 0.05 corrected using the FWE correction for the whole brain. (c) At a less stringent uncorrected threshold of P < 0.001, reduced gray matter volume was seen in the left anterior temporal gyrus (BA 38/21) and the left Sylvian fissure, in addition to the left middle frontal gyrus. (e-g) ROI analysis of gray matter volume difference in the left posterior temporoparietal region (in green), the left middle temporal gyrus (in yellow), and the left inferior occipito-temporal cortex (in orange). No significant alteration was observed in these regions. View larger image
The study compared dyslexic children who are readers of Chinese to those of English, indicating structural and functional differences between the two groups. The researchers assert that the differences in brain imaging findings imply that dyslexia may be a different neurological condition in each group, and go further to suggest that this may lead to useful clues for further genetic studies in dyslexia. According to the paper,
This study has provided insights into our knowledge of associations between structural and functional abnormalities in dyslexic individuals that may yield neurobiological clues to the cause of developmental dyslexia. The fact that Chinese and Western dyslexics show structural abnormalities in different brain regions suggests that dyslexia may even be two different brain disorders in the two cultures.
However, this may be backwards. Differences in both neural number and neural connectivity in the brain are likely to result from different uses and behaviors. In other words, dyslexia could be a condition caused by something, which in turn changes processing patterns, which in turn results in the differences seen in these brains.
Siok, W.T., Niu, Z., Jin, Z., Perfetti, C.A., Tan, L.H. (2008). From the Cover: A structural-functional basis for dyslexia in the cortex of Chinese readers. Proceedings of the National Academy of Sciences, 105(14), 5561-5566. DOI: 10.1073/pnas.0801750105