Studying Childhood-Onset Hemidystonia

Background: \- Childhood-onset dystonia is caused by a brain injury. It causes muscle contractions and twisting movements that the person with dystonia cannot control. The term hemidystonia is used when only one side of the body is affected. When dystonia starts during childhood, the brain and nerves may not develop normally. People with hemidystonia can become disabled because of the unwanted postures and twisting that dystonia causes. More research is needed to determine how dystonia affects brain development. Objectives: \- To study brain function in people with hemidystonia. Eligibility: * Individuals between 18 and 40 years of age who developed hemidystonia before age 13. Only one wrist may be affected by hemidystonia, and participants must have at least some movement in that wrist. * Healthy volunteers at least 18 years of age. Design: * This study requires five visits to the NIH Clinical Center: a screening visit and four study visits. Each visit will last up to 3 hours. Visits will be scheduled about once a week. The study procedures may be done in any order. * Participants will be screened with a physical exam and medical history. * Participants will have the following tests: * Brain magnetic resonance imaging scan. During the scan, participants will be asked to move their hand at the wrist when they hear a tone. * Motor tests of arm movement, balance, and walking. These tests may also examine nerve development and muscle tone. * Two transcranial magnetic stimulation sessions to study the electrical activity of the muscles and brain. These sessions may also involve sensory tests. Participants will have hearing tests before the first session and after the second session. * No treatment for hemidystonia will be provided as part of this study.