Mapping brain electric micro-states in dyslexic children during reading

An important issue in current research on dyslexia is to what extent the reading deficits of dyslexic children are related to processing deficits at the sensory-visual level, at the cognitive-linguistic level or at both levels. Event-related potential mapping distinguishes the split-second processing stages during reading as brief brain-electric micro-states and can address this issue directly. Previously, conventional studies have yielded inconsistent patterns of event-related potential differences between dyslexic and control children, but most of these discrepancies could result from the widely differing methodologies. We used event-related potential mapping during silent reading of correct and incorrect sentence endings to examine the neurophysiology of sensory and cognitive processes in dyslexic and control children (n = 12/group). Selected findings from spatio-temporal analyses of map strength (global field power), map latency and map topography measured in three dimensions are presented. Both sensory-visual processes in a P110 micro-state and cognitive-linguistic processes in an early N400 micro-state were affected in dyslexic children, and processing delays, as well as qualitatively different patterns of neural activation, were found. Our findings also indicated that the use of specific cognitive tasks and of appropriate spatio-temporal analyses of event-related map series are critical factors for successful identification of specific processing deficits in brain mapping studies.