<qa>  What type of movement disorder can be induced by a specific trigger?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. 