Using Structural MRI to Examine the Neural Bases of Dyslexia, Dyscalculia, and ADHD in Children

Abstract

The neuroanatomical differences associated with the developmental disorder attention-deficit/hyperactivity disorder (ADHD) or the learning disabilities (LDs) dyslexia (or reading disability, RD) or dyscalculia (or math disability, MD) have been well characterized. ADHD, RD, and MD tend to co-occur, yet the neural profile of children in whom two disorders present simultaneously is not understood, even though this information would help advance our understanding of these conditions in isolation and in their co-occurring forms. This dissertation presents three studies. First, we compared gray matter volume (GMV) in children with LD+ADHD and LD-only. Based on prior GMV studies of ADHD (compared to controls), we expected to find less GMV in the basal ganglia, but did not, leading us to conclude that behavioral difficulties around inattention/hyperactivity emanated from their LD, rather than the fronto-striatal pathology characteristic of ADHD. Second, we compared GMV in children with RD+MD and RD-only. This time we expected to find lower GMV in the intraparietal sulcus, based on prior GMV studies of MD (compared to controls), but our results did not confirm this additive model. They also did not support other models, including one that states that MD in children with RD emanates from GMV deficits in language regions. We conclude that RD+MD is likely a heterogenous group, unlikely to have common anatomical anomalies. Based on its wide utilization, we measured GMV in the first two studies, but cortical thickness (CT) reveals more anatomical detail. The two programs widely used to measure CT have not yet been formally compared in children the way they have in adults. Third, we tested for correlations and differences between CT values generated from FreeSurfer and the Computational Anatomy Toolbox (CAT12) and found high correspondence between these two programs in children. We also observed lower CT values from FreeSurfer compared to CAT12, consistent with some but not all of the studies in adults. In sum, results from the first two studies have important implications for the etiology and treatment of LD+ADHD and RD+MD. The last study provides important information on CT measures to guide future neuroanatomical studies of children.