Deep brain stimulation (DBS) of the globus pallidus interna (GPi) or subthalamic nucleus (STN) has been accepted as the surgical treatment of choice for patients with advanced Parkinson's Disease (PD), demonstrating improvements in motor function that exceed those achieved by medical management alone. Unfortunately, a paucity of data exist comparing non-motor outcomes between DBS of the available targets. Specifically, a high prevalence of concurrent cognitive dysfunction or early dementia exists in PD patients, and it is unclear whether DBS target selection may have differential effects with regards to cognitive outcomes in PD patients with early evidence of mild cognitive impairment Previous studies indicate that stimulation of either the GPi or STN is associated with decrements in patients' verbal fluency, visuospatial memory, as well as overall cognitive decline, but those patients were randomized without consideration for baseline neurocognitive performance and it is unclear whether these effects are due to treatment or rather the natural history of these patients.