“Until now, the main theory in the literature was that dyslexia in all languages would have a single universal biological origin,” said Li-Hai Tan, a research fellow at the National Institute of Mental Health. But those studies looked only at dyslexics who spoke alphabet-based languages, like English. Learning to speak Chinese is a different mental task, requiring the memorization of about 5,000 to 6,000 characters. 　　Chinese requires much more visual processing than English, which relies more on stringing sounds together. In English, we learn that words are made up of chunks and that you can come across a word you've never seen before and apply the rules. That doesn't work in Chinese; you really have to memorize the characters. Tan found differences in patterns of brain activity between normal Chinese readers and English readers. Speculating that the contrasts might hold for learning disorders, he carried out a research, brain scanning 16 children studying Chinese characters. Half of the subjects were normal readers, the other eight were dyslexic.  　　Both groups had normal activity in the left temporoparietal cortex. But the dyslexic children showed glitches in a separate region, the left middle frontal gyros. The findings suggest a person can be dyslexic in one language but not in another. But Tan has found evidence that bilingual speakers use one brain region for different languages. He showed that Chinese speakers learning English use the left middle frontal cortex―not the left temporoparietal cortex, which native English speakers use. 　　Based on this, he said, a person who is dyslexic in Chinese can not have difficulty reading  English, but it is too soon to tell. “What we know is that dyslexics tend to be quite a heterogeneous group,” Eden said. “With English dyslexics, the areas of the brain affected are multiple. And with Chinese, we're probably looking at several different areas that are affected as well.”