PROTOCOL OUTLINE: Patients undergo surgery to implant a brain stimulation system consisting of an implanted pulse generator (IPG) in the chest and a wire lead in the globus pallidum internal. After the lead has been implanted, the brain stimulation system is tested. Patients are examined at 1, 3, 6, 9, and 12 months after surgery. A double blinded evaluation, during which the IPG is either off or on, is carried out at 3 and 6 months.