Phase II Subthalamic Nucleus (STN) vs. Globus Pallidus (GPi) Trial

Inclusion Criteria:

• idiopathic Parkinson's Disease
• Hoehn and Yahr stage 2 or worse when off medications
• L-dopa responsive with clearly defined "on" periods (i.e. symptoms improve at least partially with L-dopa administration, a characteristic that helps distinguish idiopathic PD from "Parkinson's Plus" and atypical Parkinson's syndromes-see below)
• persistent disabling symptoms (e.g. on troubling dyskinesias, or disabling "off" periods at least 3 hours/day) despite medication therapy. Patients will have been treated with variable doses of levodopa and dopamine agonists (at a minimum) and will have had an adequate trial of other adjunctive medications)
• stable on medical therapy for at least one month prior to study enrollment
• age >21
• available and willing to be followed-up according to study protocol

Exclusion Criteria:

• "Parkinson's plus" syndromes, secondary, or atypical Parkinson's syndromes (e.g. progressive supranuclear palsy, striato-nigral degeneration, multiple system atrophy, post-stroke, post-traumatic, or post-encephalitic Parkinson's. These patients have cardinal symptoms characteristic of PD but with additional symptoms indicating other organic brain dysfunction, such as gaze palsies, autonomic dysfunction, lack of response to L-dopa, these individuals tend not to improve with standard treatments for PD)
• previous Parkinson's Disease surgery
• medical contraindications to surgery or stimulation (e.g. uncontrolled hypertension, advanced coronary artery disease, other implanted stimulation or electronically-controlled devices including cardiac demand pacemaker, aneurysm clips, cochlear implants, or a spinal cord stimulator) (Note: for the subject who receives either a pacemaker and/or defibrillator after this study enrollment, he/she will be allowed to continue the study if the neurostimulator system can be adequately programmed to permit system compatibility)
• contraindication to magnetic resonance imaging (e.g. indwelling metal fragments or implants that might be affected by MRI)
• active alcohol or drug abuse
• score on Mini-Mental Status examination of 24 or lower, or other neuropsychological dysfunction 9e.g. dementia) that would contraindicate surgery
• intracranial abnormalities that would contraindicate surgery (e.g. stroke, tumor, vascular abnormality affecting the target area)
• pregnancy
• concurrent participation in another research protocol