Deep Brain Stimulation for Parkinson's Disease

* INCLUSION CRITERIA: To be eligible for entry into the study, candidates must meet all the following criteria: * Be 18 years of age or older. * Able to comply with study procedures and provide informed consent. * Have a clinical diagnosis of idiopathic PD, primary dystonia, or ET: 1. The diagnosis of idiopathic PD will be based on the UK Brain Bank Criteria, and confirmed by the Movement Disorders Neurologists in the NIH Parkinson Clinic. 2. The diagnosis of primary (generalized or segmental), hemidystonia, or cervical dystonia will be confirmed on clinical examination in the NIH Movement Disorders Clinic. 3. The diagnosis of ET will be confirmed on clinical examination in the NIH Movement Disorders Clinic (the diagnosis of ET will be based on bilateral, largely symmetric postural or kinetic tremor involving hands and forearms that is visible and persistent. Additional or isolated tremor in head may be present but there should be the absence of abnormal posturing). * a. History of appropriate response to dopaminergic medication, with at least a 30% improvement in motor UPDRS with L-DOPA by history or in-clinic testing, for the PD patients. OR b.Patients with tremor-dominant PD that do not respond to dopaminergic therapy and that exhibit a tremor score of at least 2 for tremor severity on at least one side of the body on the motor UPDRS examination. * Unsatisfactory clinical response to maximal medical management (with trials of both higher and lower doses of drugs), including: For PD patients: 1. good benefit from dopaminergic medication but associated with insufficient duration of action or unacceptable side-effects OR 2. intractable disabling motor fluctuations (severe off periods, dyskinesias, or freezing spells) OR For ET and dystonia: 3. intractable symptoms of ET or dystonia impacting at least 2 activities of daily living. * Interested in being evaluated to undergo DBS, if indicated, to treat medically refractory movement disorder or * Patients already implanted with DBS for continued management (Note: Inclusion criteria 4 and 5 can be met by historical report in patients who had DBS implanted outside the NIH) EXCLUSION CRITERIA: For those who have not had DBS: Candidates will be excluded if they meet any of the following criteria: * Clinically significant medical disease that would increase the risk of developing pre- or postoperative complications, including but not limited to uncontrolled systemic hypertension with values above 170/100; unstable heart disease; unstable respiratory disease; uncorrected coagulation abnormalities or need for therapeutic anticoagulation which cannot be interrupted; * Evidence of secondary or atypical parkinsonism/dystonia/tremor as suggested by: 1. History of stroke, exposure to toxins, neuroleptics, or encephalitis 2. Neurologic signs of upper motor neuron or cerebellar involvement, supranuclear gaze palsy, or multiple systems atrophy. 3. MR-imaging with evidence indicative of secondary disease such as tumor, or stroke, which could cause the movement disorder. * Dementia as evidenced by formal neuropsychological evaluation, Mattis Dementia Rating Scale (DRS-2) score, and clinical evaluations. * Unable to complete cognitive assessments and testing necessary to adequately evaluate risks and benefits of surgery. * Clinically signficiant or unstable psychiatric disorder such as severe depression or anxiety, which, in the opinion of the investigators would increase the risk of developing postoperative complications. * Unable to undergo MR-imaging because of implanted pacemakers, medication pumps, aneurysm clips, metallic prostheses (including metal pins and rods, heart valves or cochlear implants), shrapnel fragments, permanent eye liner or small metal fragments in the eye that welders and other metal workers may have, or if candidates are uncomfortable in small closed spaces (have claustrophobia), or cannot lie comfortably on their back for up to one hour. * Pregnant women. * Otherwise not eligible for DBS surgery, for example known inability to undergo anesthesia For those who have had DBS: -Contra-indications for ongoing stimulation, such as intractable side effects of DBS despite stimulation parameter adjustment