This study will use three neurophysiological tests (see below) to determine what areas of the brain are responsible for paroxysmal hyperkinetic movement disorders. Patients with these disorders have sudden, brief attacks of movement, similar to epileptic seizures, but without loss of consciousness. Normal volunteers and patients with two subtypes of paroxysmal hyperkinetic movement disorder, paroxysmal dyskinesia and psychogenic variant, that can be induced by a specific trigger, such as a sudden movement or prolonged exercise, will be included in this study. Candidates must be 12 years of age or older. Women of childbearing potential will be screened with a pregnancy test. Participants will undergo one or more of the procedures detailed below. Patients' test results will be compared with those of normal volunteers. Before each test, participants will provide a medical history and undergo a brief physical examination. During each procedure, the subject will have surface electromyography (EMG) to measure the electrical activity of muscles. For EMG, electrodes (metal discs) filled with a conductive gel are taped to the skin over the muscle to be evaluated. Functional Magnetic Resonance Imaging (fMRI) MRI uses a strong magnetic field, radio waves, and computer technology to provide detailed images of the brain. For this test, the subject lies in a narrow cylinder (the scanner), while pictures of the brain are taken. Earplugs are worn to muffle loud noises caused by electrical switching of radio frequency circuits used in the scanning process. For functional MRI (fMRI), the subject is asked to mimic a movement that occurs during an attack, such as stiffening the hand to make a fist or flexing and rotating the arm inward, to detect changes in the brain regions involved in the movement. During the procedure, involuntary movements and voluntary movements will be monitored by surface EMG and by video camera. The test will last about 1-1/2 hours. Electroencephalography (EEG) EEG measures the electrical activity of the brain (brain waves) with electrodes placed on the scalp. During the procedure, muscle activity will be recorded with EMG. The subject will first relax and then will be asked to mimic a movement attack. The test will last from 1-1/2 to 2 hours. Startle Reflex The subject will put on a headphone and hear loud noises in a random fashion. During the test, muscle activity will be recorded with EMG and with a video c...
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