Cerebral mechanisms involved in word reading in dyslexic children: a magnetic source imaging approach.

The purpose of the present investigation was to describe spatiotemporal brain activation profiles during word reading using magnetic source imaging (MSI). Ten right-handed dyslexic children with severe phonological decoding problems and eight age-matched non-impaired readers were tested in two recognition tasks, one involving spoken and the other printed words. Dyslexic children's activation profiles during the printed word recognition task consistently featured activation of the left basal temporal cortices followed by activation of the right temporoparietal areas (including the angular gyrus). Non-impaired readers showed predominant activation of left basal followed by left temporoparietal activation. In addition, we were able to rule out the hypothesis that hypoactivation of left temporoparietal areas in dyslexics was due to a more general cerebral dysfunction in these areas. Rather, it seems likely that reading difficulties in developmental dyslexia are associated with an aberrant pattern of functional connectivity between brain areas normally involved in reading, namely ventral visual association cortex and temporoparietal areas in the left hemisphere. The interindividual consistency of activation profiles characteristic of children with dyslexia underlines the potential utility of this technique for examining neurophysiological changes in response to specific educational intervention approaches.