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
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You write that "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." We're the speakers in question native speakers of both languages? If I recall, we use different areas of the brain for native languages as opposed to languages learned later in life. So if the people in question were native speakers of only one language, couldn't such damage have selectively damaged an area used only for native or non-native languages?
"has provided insights into our knowledge of associations between structural and functional abnormalities in dyslexic individuals"...I think that is all I would feel safe saying; the rest is conjecture.
"suggests that dyslexia may even be two different brain disorders in the two cultures"
My red flag goes up when I read or hear that a bio or psychogenic disorder is 'different across culture.' That in and of itself makes me cautious, if only because it implies false 'race' factors and makes me wonder if the researchers studied the same thing.
"dyslexia could be a condition caused by something, which in turn changes processing patterns, which in turn results in the differences"hmmm...there are three main types of dyslexia, and some of them are caused directly( in the case of trauma dyslexia)
The basic idea as I understand it is that it is likely genetic; but (Greg, you will love this one--from a homeschool perspective) some say it is caused by 'teaching methods', as opposed to exacerbated by them;-)
http://www.sntp.net/education/look_say_3.htm
As the dyslexia research community generally stays focused in investigating one area of the brain at a time
this study should help promote the concept that particular dyslexics have particular difficulties generated in particular areas of the brain.
I would be interested in whether the cultural and reading style differences show the same result of being able to see differences in Chinese dyslexics and English dyslexics as groups but without the ability to identify a dyslexic as either Chinese or English. This seems to be the common result with fMRI results when looking at one area of the brain with dyslexics and non dyslexics because of the overlap of results.
Could it also be possible to identify a brain as being Chinese or English by MRI and what might be learned from that fact ? If so are the same differences also seen in infants?
Doesn't this simply mean that phonetic (English) and ideographic (Chinese) writing systems are processed in different areas of the brain?
An interesting case is Japanese, which uses combination of phonetic symbols (hiragana and katakana) and ideographic symbols (kanji = Chinese characters). It is known (I suppose from studying patients with alexia) that lesions in one area of the brain disrupt reading of hiragana and katakana (phonetic writing) but leave comprehension of kanji (ideographic writing) largely intact. So, it makes a lot of sense that dyslexia in English and Chinese readers are caused by different abnormalities in the brain.
Josh: I don't think we know what you say for certain across ideographic vs. alphabet based languages. The specific cases I know of with stroke damage involved Chinese individuals who learned English later than the Chinese.
Yes, it does imply that we use different areas of the brain depending on what kind of language we speak. My problem with his is that the researchers seem to have a causal model that runs: Gene(or something) causes disease in a particular part of the brain, which causes a syndrome (dyslexia). My alternative suggestion is that something (genetic or developmental) causes language dyslexia no matter where the language function is distributed, which causes a different language function than "normal" which causes rearrangement of neurons. Thus, the neural rearrangement would be in different parts of the brain if those language functions are distributed in different parts of the brain.
John: I would predict that the differences would not be visible in infants because infants are not English or Chinese speakers yet.
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