Structural and Functional Aspects of Brain Development in Children with an Autism Spectrum Disorder (ASD)

Research suggests that brain growth follows an abnormal trajectory in children with autism spectrum disorders (ASD). A better understanding of when and how patterns of brain development diverge from that seen in typically developing children could yield insight into the etiology of the disorder, and resulting symptomatology. To investigate this hypothesis, three studies examined the relation between structural and functional brain measures and age in a group of children with an ASD, aged 6 to 14 years. Age by group interactions were found in all three studies, providing further evidence that brain development may follow an atypical trajectory in ASD. Study 1: Differences in the relation between structural indices and age were found in grey matter volume, surface area and thickness, as well as in cortical thickness of specific regions in the left inferior frontal gyrus (BA 44) and left precuneus. These measures of grey matter structure generally decreased with age in the ASD children, compared to little or no change with age in the typically developing children. Study 2: Differences in the relation between age and measures of longitudinal, radial and mean diffusivity were found in frontal, long distant, interhemispheric and posterior white matter tracts; diffusivity decreased with age in the typically developing group, but showed little or no change in the ASD group. Study 3: Differences in the relation between BOLD activation on a set-shifting task and age were found in brain regions important for cognitive flexibility, such as areas of prefrontal, right insula and parietal cortex. These effects were mainly due to decreasing activation with age for the ASD group, but increasing or no age-related change in the TD group. The findings of these three studies provide converging evidence in support of an hypothesis of dysregulated brain development in this population, which could have significant, compounding effects on the development of neural connectivity, and contribute to atypical cognitive development in children with ASD.Ph