This study will use functional magnetic resonance imaging (fMRI) to examine what happens in the brains of adolescents when they are exposed to violent media and how imagining aggressive behavior affects brain function. The study will measure physiological changes (such as the amount of electricity generated by the skin, heart rate, and breathing rate) related to these tasks during fMRI. MRI uses a magnetic field and radio waves to obtain images of body organs and tissues. For fMRI, the subject performs certain tasks during the MRI scanning to examine changes in the brain regions that are involved with those tasks. During the scan, the subject lies in a metal cylinder (the scanner), wearing earplugs to muffle loud noises that occur with the scanning.

Healthy right-handed native English-speaking males between 14 and 17 years of age may be eligible for this study. Candidates are screened with a neurological examination and neuropsychological testing that includes questions about their feelings, experiences, and behavior, and tests of reading level and intelligence.

Participants undergo fMRI and fill out questionnaires before and after the scanning. Some children are asked to play 20 minutes of video games before the test. During the scan, the child views short neutral video clips and video clips of people fighting or imagine self-defense situations. The child is asked to rate the video clips for their aggressive content or tell how he or she feels about the imagined situations. Two small straps are wrapped around the child's index and middle fingers to measure changes in the amount of electricity generated by the skin, and a strap at the ring finger measures the child's heart rate. A band around the child's chest records breathing rates.

Children who cannot or do not want to undergo MRI testing may be asked to view commercially available video clips of people fighting and neutral video scenes, such as sports scenes. They are asked to rate them on their violent content and excitement, or to rate the video games they have played on their violent/nonviolent content and their popularity. In addition, the children fill out questionnaires about their media use and exposure to violence.

All participating families are contacted by telephone 1 day and 2 weeks after the experiment for parents to answer questions about how the child has been doing and for the children to answer questions about their feelings.