Investigating the Impact of Methylphenidate on Neural Response in Disruptive Behavioral Disorder

Background: \- Disruptive behavior is a common problem for children and adolescents. It can be treated with some success with stimulant medicine. Researchers want to learn more about how this works. Objective: \- To learn how the brain changes when taking the medicine methylphenidate for behavior problems. Eligibility: * Children ages 10 17 with conduct disorder and/or attention deficit disorder. * Healthy volunteers the same age. Design: * Participants will be screened under a separate protocol. * Participants will have two 3-hour sessions at the clinic. Girls who are menstruating will have a pregnancy test before their scans. * Visit 1: All participants will: * Perform simple tests on a computer. * Fill out a questionnaire along with their parent or guardian. * Have an MRI scan. A magnetic field and radio waves take pictures of the brain. Participants will lie on a table that slides into a metal cylinder. A coil will be placed over their head. They will be in the scanner for 60 minutes, lying still or performing a simple task. They will practice the task before the scan. A computer screen will show them task information during the scan. The scanner makes loud knocking sounds. Participants will get earplugs. Their parent or guardian can stay with them during the scan. * Only participants with behavior disorders will: * Take a pill of the study medicine or placebo. * Be monitored for any side effects. * Visit 2 is a repeat of Visit 1, except participants who got a pill in Visit 1 will get the other pill in Visit 2. For healthy volunteers, the 2 visits are exactly the same.