Deep Brain Stimulation (DBS) of the Pedunculopontine Nucleus (PPN)

This is a mechanistic study to determine the differential effects of the dopaminergic and cholinergic systems on attention, gait, and balance. The primary goal of the study is to evaluate the relative effects of pedunculopontine nucleus (PPN) and subthalamic nucleus (STN) Deep Brain Stimulation (DBS) on these features in persons with Parkinson's Disease (PD) who are eligible for DBS for improvement of their motor symptoms and exhibit gait instability with falls. Patients will be enrolled and implanted with bilateral electrodes in one of the approved DBS locations (subthalamic nucleus: STN), but additionally electrodes will be inserted into the experimental target, namely the PPN bilaterally.