Biological abnormality of impaired reading is constrained by culture

Developmental dyslexia is characterized by a severe reading problem in people who have normal intelligence and schooling(1-3). Impaired reading of alphabetic scripts is associated with dysfunction of left temporoparietal brain regions(2-5). These regions perform phonemic analysis and conversion of written symbols to phonological units of speech (grapheme-to-phoneme conversion); two central cognitive processes that mediate reading acquisition(6-7). Furthermore, it has been assumed that, in contrast to cultural diversities, dyslexia in different languages has a universal biological origin(1,8). Here we show using functional magnetic resonance imaging with reading-impaired Chinese children and associated controls, that functional disruption of the left middle frontal gyrus is associated with impaired reading of the Chinese language ( a logographic rather than alphabetic writing system). Reading impairment in Chinese is manifested by two deficits: one relating to the conversion of graphic form ( orthography) to syllable, and the other concerning orthography-to-semantics mapping. Both of these processes are critically mediated by the left middle frontal gyrus, which functions as a centre for fluent Chinese reading(9-11) that coordinates and integrates various information about written characters in verbal and spatial working memory. This finding provides an insight into the fundamental pathophysiology of dyslexia by suggesting that rather than having a universal origin, the biological abnormality of impaired reading is dependent on culture.