Effects of lexicality and word frequency on brain activation in dyslexic readers.

We investigated the neural basis of lexical access to written stimuli in adult dyslexics and normal readers via the Lexicality effect (pseudowords>words) and the Frequency effect (low>high frequent words). The participants read aloud German words (with low or high lexical frequency) or pseudowords while being scanned. In both groups, both Lexicality effect and Frequency effect involved Broca's region (areas 44 and 45). Whereas the effects were stronger for dyslexic than normal readers in area 44, area 45 showed the reverse pattern. These findings mimic recent results from an fMRI study on dyslexic primary school children, indicating that lexical access to written stimuli poses increased and enduring difficulties on dyslexic readers, at least in a language with a transparent orthography. Additionally, data from four compensated adult dyslexics are reported and discussed, which hint at the importance of both Broca's and Wernicke's region for recovery from childhood dyslexia.