This is an Individual National Research Service Award, which provides postdoctoral research training to individuals to broaden their scientific background and extend their potential for research in specified health-related areas. Although many brain regions are likely involved in autism spectrum disorders (ASD), the amygdala has been an area of great interest due to its role in emotional behavior and its numerous connections to other brain regions also implicated in ASD. Abnormal amygdala function has been demonstrated in ASD subjects and initial studies have identified altered amygdala anatomy in post-mortem tissue from adults with ASD. In addition, several magnetic resonance imaging (MRI) studies demonstrate that the amygdala is enlarged in young individuals with ASD. Studies employing a technique known as diffusion tensor imaging (DTI), which allows for visualization and investigation of pathways in the brain, have already begun to identify abnormalities in the brains of adults with ASD. However, no studies have yet investigated amygdala connectivity early in life when ASD symptoms first emerge and when abnormal enlargement of the amygdala is most pronounced. The proposed research will utilize DTI to investigate amygdala connectivity in a large longitudinal group of preschool-aged children with ASD and typically developing children. The proposed research will contribute significantly to current knowledge of amygdala abnormalities in ASD. In addition, by examining neural pathways in a large group of children with ASD, this study will further identify specific subtypes of neuropathology in ASD.