Dyslexia as neurologic deficit

Abstract

In the search for a universal neurologic basis for dyslexia despite differences in prevalence amongst countries, an international research team found that English, French, and Italian individuals with demonstrated reading and phonological deficits also exhibit decreased left brain activity by PET scan. During reading and naming tasks, they show reduced activation in the left temporal lobe and middle occipital gyrus compared with normal readers. Why, then, is dyslexia so less prevelant in Italy compared with France, the UK or the US? The authors of the March 16 Science article argue that the same phonological deficits are more likely to cause literacy problems in languages with more irregular writing systems. Therefore, individuals with deficits would have more trouble with English, in which 40 sounds are represented by over a thousand different letter combinations and some of them arbitrarily. By comparison, Italian has less ambiguity and uses only 33 combinations for 25 sounds.