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Diffusion Tensor Tracking of Connectivity Abnormalities in Autism

Recent functional imaging studies (fMRI) have revealed a reduction in functional connectivity across cortical brain regions involved in language, problem solving, and social cognition; simple tasks showed normal connectivity. Structural brain studies have shown an increase in brain volume attributable largely to an increase in the outer white matter zone. This white matter connects immediately adjacent areas of cortex and makes longer distant connections between cortical regions within the same hemisphere. The corpus callosum, the major white matter pathway connecting the two hemispheres, is smaller in autism. This study investigated white matter connections using a new method called diffusion tensor fiber tracking to map white matter pathways related to each of the major symptom areas of autism. The size, shape and density of these pathways in high functioning teens and adults with autism were compared to matched normal controls and behavioral indices. The hope was that this study would advance the understanding of connectivity in autism, pave the way for comparisons with functional connectivity, guide developmental neurobiologic studies, and provide an index for future cognitive rehabilitation strategies designed to enhance connectivity.