Employing Near Infrared Spectroscopy to Non-invasively Assess Changes in Cerebral Perfusion in Response to Subthalamic Deep Brain Stimulation

The investigators will study the effects of electrical stimulation at the subthalamic nucleus on frontal cerebral perfusion in 10 patients with advanced PD who have already undergone successful STN DBS (Medtronic, Inc., Minneapolis, MN) surgery as evidenced by a 20% or greater improvement in their Unified Parkinson's disease rating scale (UPDRS) motor sub-score (UPDRS-III) with stimulation on vs off, three or more months after surgery. The UPDRS-III is a widely employed and validated rating scale of Parkinson's disease symptom severity that is based on the neurological examination. For the purposes of this study, a movement disorders neurologist will perform all of the neurological assessments. Patients must also be demonstrated to be cognitively intact as evidenced by a Montreal Cognitive Assessment (MoCA) Score of 24 or greater.

This is an experimental study in which we will compare frontal cerebral perfusion (measured non-invasively with the NIRS device) and UPDRS-III scores (as determined by neurological examination) in four clinical states: medications off/stimulation off; medication off/stimulation on; medication on/stimulation off; and medications on/stimulation on.

The primary question to be answered is: Can we detect significant changes in cerebral perfusion with the NIRS device in response to subthalamic stimulation delivered via implanted DBS devices?

This pilot study will be conducted in 10 PD patients who have undergone successful DBS surgery in the past. The study will be completed in one day as detailed below and will take about 6 hours to complete.

Patients will arrive to the movement disorders center on the morning of their scheduled study visit having discontinued their medications from the night before (12 hours 'off"). They will arrive with their stimulators on and set to the therapeutic parameters. Dr. Shih will perform a neurological examination and determine the UPDRS-III score in this, the off med/on stim state.