[Survey of fMRI results regarding a phonological deficit in children and adults with dyslexia: fundamental deficit or indication of compensation?].

Early neuroimaging studies exploring the neurobiological correlates of the phonological deficit in dyslexia were restricted to adult probands with dyslexia due to the exposure to radioactivity in the course of PET measurements. The differences in activation between normal adult readers and adults with dyslexia recorded in these studies left open the issue of whether or not these are indeed fundamental activation deficits or only a reflection of lifelong experience with poor reading and writing skills and thus should be interpreted as a sign of compensation. Development of fMRI in recent years has enabled the investigation of children with dyslexia in order to explore the neurobiological activation patterns that underlie dyslexia. On the whole, the imaging findings in children and adults with dyslexia indicate that the left-hemisphere inferior frontal differences in activation, as well as the dorsal and ventral temporal differences in activation observed in all age groups during the processing of phonological language tasks are to be regarded as a fundamental biological deficit in dyslexia. Right-hemisphere differences in activation, which in German-speaking areas are observable in adults but only rarely in children with dyslexia, might, on the other hand, be regarded as a sign of developmental compensation.