A research study involving children and adolescents (ages 6 - 18 years) with a diagnosis of an autism spectrum disorder. This study is looking at the effects of an investigational medication on the brain. Oxytocin (nasal spray) is thought to help with social behaviors. This study is looking specifically at the effects of oxytocin vs. placebo on various brain activities. Participants will receive either one dose of oxytocin or one dose of placebo (saline solution with no medicine) followed by brain scans and behavioral assessments.