Atypical neurodevelopment in auditory and language cortex and the corpus callosum in autism

Abnormalities in language and communication, auditory sensitivity, and complex information processing are associated with autism, yet the neural underpinnings are unknown. The studies in this dissertation examine neurodevelopment of several brain regions implicated in these abnormalities. We first examine age-related changes in midsagittal corpus callosum area in a large cross-sectional cohort from early childhood to adulthood. Increased variability in total corpus callosum area and atypical regional development in the rostrum and isthmus are found in autism compared with typical controls. In autism, larger areas are associated with reduced severity of autism behaviors, higher intelligence, and faster speed of processing, providing support to theories of underconnectivity in the autism brain. Longitudinal maturation of Heschl's gyrus gray matter and white matter and planum temporale during childhood and adolescence in autism and a typically developing sample are then described. Despite previous cross-sectional studies reporting typical Heschl's gyrus structure in autism, reduced developmental trajectories in the right gray matter and atypical white matter maturation are identified. Our longitudinal findings also expand on previous reports of reduced planum temporale asymmetry in autism by showing that the reduced asymmetry develops during later childhood and adolescence. In addition to the case-control comparisons, different developmental trajectories in those individuals with autism with delayed versus early language onset in Heschl's gyrus white matter and planum temporale asymmetry are apparent. Finally, individuals with autism exhibit associations between smaller Heschl's gyrus volumes and reduced auditory sensitivity and higher language function, and smaller planum temporale volumes associated with increased vocabulary aptitude. Our findings highlight the importance of longitudinal studies of brain development and examining behavioral profiles of individuals to identify functional and maladaptive pathological neurodevelopment.