FUNCTIONAL DISRUPTION IN THE ORGANIZATION OF THE BRAIN FOR READING INDYSLEXIA

Learning to read requires an awareness that spoken words can be decomp osed into the phonologic constituents that the alphabetic characters r epresent. Such phonologic awareness is characteristically lacking in d yslexic readers who, therefore, have difficulty mapping the alphabetic characters onto the spoken word. To find the location and extent of t he functional disruption in neural systems that underlies this impairm ent, we used functional magnetic resonance imaging to compare brain ac tivation patterns in dyslexic and nonimpaired subjects as they perform ed tasks that made progressively greater demands on phonologic analysi s. Brain activation patterns differed significantly between the groups with dyslexic readers showing relative underactivation in posterior r egions (Wernicke's area, the angular gyrus, and striate cortex) and re lative overactivation in an anterior region (inferior frontal gyrus). These results support a conclusion that the impairment in dyslexia is phonologic in nature and that these brain activation patterns may prov ide a neural signature for this impairment.