Cross-cultural Dyslexia
Dyslexics transpose letters as they read, making reading difficult. At least that's what happens with English-speaking dyslexics, but Chinese with dyslexia are more likely to have difficulty converting a symbol into sound and meaning. Earlier research showed that English-speaking dyslexics have reduced activity in temporo-parietal language areas. But researchers at the University of Hong Kong using functional MRI discovered that activity is not reduced in those areas in Chinese dyslexics but in the left middle frontal gyrus, known to be important in reading Chinese characters; there is also a significant reduction in gray matter volume in the frontal area, compared to non-dyslexic controls. If you were bilingual in English and Chinese and dyslexic in one of the languages, would you be dyslexic in the other? Research leader Li Hai Tan thinks not, because he believes different genes are responsible for the two dyslexias. Proceedings of the National Academy of Sciences, Vol 105, 5561-5566.
A Brain for Language
Chapter 9 makes the point that some non-human animals possess brain structures similar to those involved in human language. It also makes the point that language is a product of complex interactions among these structures, and a recent study indicates that non-human animals may have a deficiency here. In humans, Wernicke's area communicates with Broca's area via bundles of neural fibers that make up the arcuate fasciculus (see Fig 9.20). Imaging showed that the arcuate fasciculus also exists in chimps and macaque monkeys, but in chimps it makes only limited connections to temporal lobe areas comparable to Wernicke's area, and there is little evidence of these connections in macaques. The researchers suggest that strong connections between Wernicke's and Broca's areas enabled our development of language. Nature Neuroscience, Vol 11, 426-428.
