In this study, researchers are looking at how Deep Brain Stimulation (DBS), a treatment that uses electrical signals to help brain function, affects long-term behavior and thinking in people with Parkinson's Disease (PD). PD is a disorder that affects movement, causing symptoms like shaking and stiffness. The study will last for five years, with assessments conducted once a year. It will compare two groups of patients: those receiving DBS in the subthalamic nucleus (STN), which is a part of the brain, and those on the best available medical treatment.

• The study requires annual visits over a 5-year period.
• Participants must either be candidates for DBS or currently undergoing the best medical treatment.
• Participants who cannot complete study assessments will not be eligible.