Atypical brain activation of reading processes in children with developmental dyslexia.

Brain activation differences of reading-related processes between dyslexic and normal reading children were localized with functional magnetic resonance imaging (MRI). The children performed tasks that varied in visuospatial, orthographic, phonologic, and semantic processing demands. Enhanced activation of the left extrastriate cortex was found during all tasks in the dyslexic group. During orthographic processing, dyslexic children predominantly showed activation in the right prefrontal cortex, as also occurred during the visuo-spatial task. Normal readers also showed activation in the left prefrontal cortex. Dyslexic readers showed less activation of both the temporal and the prefrontal cortex during phonologic processing. The results suggest that dyslexic readers fail to use brain areas that are normally specialized in language processing, but rather use areas that underlie visuospatial processing.