Neurophysiology of Task-Specificity of Focal Hand Dystonia

This study will examine how the brain coordinates movement in patients with focal hand dystonia. Patients with dystonia have muscle spasms that cause uncontrolled twisting and repetitive movement or abnormal postures. In focal dystonia, just one part of the body, such as the hand, neck or face, is involved. This study will use transcranial magnetic stimulation (TMS, see below) to study how the brain plans movement. Healthy volunteers and patients with focal hand dystonia 18 years of age and older may be eligible for this study. Healthy subjects may participate in one, two or three of the experiments described below. Patients with dystonia may participate in experiments one and three. Before each experiment, each subject is asked about his/her medical and neurologic history, complete questionnaires and will undergo a brief physical examination. Experiment 1

• Surface EMG: Small electrodes are taped to the skin over the arm to measure the electrical activity of muscles.
• TMS: A wire coil is held on the subject's scalp. A brief electrical current is passed through the coil, creating a magnetic pulse that stimulates the brain. During the stimulation, the subject may be asked to tense certain muscles slightly or perform other simple actions. The stimulation may cause a twitch in muscles of the face, arm, or leg, and the subject may hear a click and feel a pulling sensation on the skin under the coil. Experiment 2 (Two visits.)
• Visit 1: Magnetic resonance imaging (MRI): This test uses a magnetic field and radio waves to obtain images of body tissues and organs. The patient lies on a table that is moved into the scanner (a metal cylinder), wearing earplugs to muffle loud knocking and thumping sounds that occur during the scanning process. The procedure lasts about 90 minutes, during which time the patient will be asked to lie still for up to 30 minutes at a time.
• Visit 2: Surface EMG and TMS Experiment 3
• Surface EMG and TMS - During the TMS, subjects are asked to respond to shapes on a computer screen by pushing a button or pressing a foot petal.