FUNCTIONAL MRI STUDIES OF THE PATHOPHYSIOLOGY OF DYSLEXIA IN ADULTS

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This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Developmental dyslexia is a common disorder of reading whose etiology is poorly understood. The behavioral manifestations of dyslexia are complex, involving abnormalities in both language and visual perception. It is well known that reading ability is correlated with measures of phonological awareness. Because dyslexics exhibit abnormalities in various forms of phonological processing, this has been suggested as an explanation for their reading disability. While less clinically evident, specific visual processing problems have also been identified in dyslexia and it has been suggested that they contribute to the observed reading disorder. Surprisingly, few functional neuroimaging techniques now provide a way to identify the regional specialization and spatial congruence of the cortical areas engaged in visual sensory and language processing. These new techniques make possible novel investigations of the pathophysiology of the reading disorder developmental dyslexia. We have undertaken a series of integrated studies combining behavioral measures with functional magnetic resonance imaging (fMRI) to investigate the relationship between the disorders in phonological processing and visual motion processing in dyslexia. In this research, functional maps obtained from control subjects during reading tasks will be compared to those obtained in individuals with dyslexia. Our central hypothesis posits the existence of a disorder in temporal information processing in dyslexia that exhibits itself in deficits in both sensory and language processing. In our previous work we have demonstrated a sensory deficit specific to the visual motion processing system. Using similar techniques are now extending these investigations and relate them to dysfunction of phonological processing mechanisms. We hypothesize that we will identify spatial overlap in the cortical areas altered in dyslexia during both phonological and visual processing in the temporoparietal areas, as this area has shown to directly subserve both sensory visual motion and cognitive language processes. Specific questions being addressed include: (1) What are the neural systems involved in phonological awareness (segmentation, rhyme generation and coding in verbal memory) and visual motion processing in normal subject? (2) Do the neural systems involved in phonological awareness show sensitivity to performance rate, modality of presentation (auditory versus visual) or response (overt versus covert)? (3) Is there spatial overlap in the neuronal systems involved in the performance of phonological awareness tasks and visual motion processing ? (4) Since performance on these tasks reliably differentiates dyslexics from controls, are the neural systems involved differently activated in dyslexics and controls during the performance of these tasks? This study will require extensive behavioral testing which will be aided by the Behavioral Phenotyping and Instrumentation Core. Data management and statistical analysis are substantial for both behavioral and fMRI data and will be aided by the Informatics/Data Management and Biostatistics core.