Humans can rapidly regulate actions according to evolving environmental demands, however, impairments of action regulation have been identified across a number of neurological disorders including Parkinson's Disease (PD). A key component of action regulation is action inhibition that occurs when stopping unwanted or inappropriate actions. There is mounting evidence that action inhibition also plays a critical part in selecting between competing alternative actions and switching to new actions in response to environmental changes. The investigators hypothesize that stop circuitry (involving frontal-subthalamic nucleus (STN) pathways) are involved in inhibiting unselected actions during action selection with competing alternatives (in the absence of overt stopping) and that switching motor plans also engages stopping circuitry (involving prefrontal-STN pathways) for cancelling the ongoing action, before changing to new one. The overall goal is to delineate the neural circuitry underlying a broad array of action regulation functions that involve inhibitory control, how these functions interrelate, and how they are implemented within brain networks. In this research, the investigator will take advantage of the unique opportunity provided by awake deep brain stimulation surgery to learn more about how the brain functions in a diseased state and how deep brain stimulation changes these networks to make movement more normal. The investigator will simultaneously assess cortical and subcortical electrophysiology in relation to clinical symptoms and behavioral measures and in response to deep brain stimulation in patients undergoing Deep Brain Stimulation (DBS) implantation surgery.

Inclusion Criteria:

• Age 18 years or older.
• Diagnosis of Parkinson's disease (rigid-akinetic subtype or tremor-dominant) based on presence of at least 2 cardinal PD features (tremor, rigidity, or bradykinesia).
• Clinical indication and decision to proceed with subthalamic nucleus deep brain stimulation implantation.
• L-dopa responsive with clearly defined "on" periods, with at least 30% improvement in UPDRS III scores on vs off medications (with documented ON UPDRS III scores).
• Willingness and ability to cooperate during conscious operative procedure for up to 30 minutes.
• Preoperative MRI without evidence of cortical or subdural adhesions or vascular abnormalities.

Exclusion Criteria:

• Patients with recent use (within one week) of anticoagulant or antiplatelet agent use.
• Neurocognitive testing indicating amnestic cognitive deficits (MOCA < 24).