This grant provides support for an NIH Autism Center of Excellence (ACE). Repetitive behaviors form a core feature of autism spectrum disorders (ASD), but the understanding of the neural basis of stereotypy and repetitive behaviors in ASD and their treatment is limited. Recently, risperidone, an antipsychotic, was observed to robustly reduce stereotypic behaviors in a sample of children and adolescents with autism. The proposed study attempts to increase understanding of repetitive behaviors in ASD and its treatment by examining the changes in key neural circuits associated with risperidone treatment using functional magnetic resonance imaging (fMRI). The proposed clinical trial and study design provide a unique opportunity to study the biology of treatment response on the target of repetitive behaviors which could cast a broader light on the nature of brain dysfunction across these similar parallel distributed brain systems and their interactions.