This study aims to determine whether direct brain stimulation of specific regions and ranges improves cognition in people with Parkinsons Disease (PD) who already have a deep brain stimulator implanted. Research activities consist of 32 subjects undergoing stimulation changes to their device and being administered neurocognitive tests to evaluate the changes. An fMRI scan will also be done at baseline and at weeks 15 and 27.

All subjects will undergo the stimulation changes in a randomized double blind crossover study. Evaluation of stimulation changes will be assessed through analysis of neurocognitive data.

In this single-center pilot study, the investigators will study both acute and chronic changes to neurocognitive and motor performance in response to interleaving gamma/theta (theta burst) stimulation compared to standard-of-care gamma stimulation.

This study will be a randomized double-blinded crossover study. Each patient's baseline voltage intensity will be unchanged. During the first outpatient visit, a baseline assessment (under baseline stimulation parameters, including frequency, pulse width and voltage) consisting of motor and cognitive tests will first be performed. After one week of titration on the theta burst stimulation paradigm, all patients will randomized to either baseline or theta burst stimulation settings for one week. Motor testing (UPDRS) and neuropsychological testing will be performed after this week. Each patient will then be programmed to the other stimulation paradigm for another week. At the end of this third week, neuropsychological and motor testing will again be performed.

Patients will again be randomized into either baseline gamma stimulation or theta burst stimulation for the chronic phase of the study. Repeat neuropsychological and motor testing will be performed at three months. Each patient will switched to the other stimulation strategy and repeat neuropsychological and motor testing will be performed after another three months. After the first 6 months, patients will be placed on open-label theta burst stimulation for 6 months (total of one year). At the end of one year, patients will undergo repeat neuropsychological and motor testing, after which they will be reprogrammed to their initial settings or given the option to remain on theta burst stimulation parameters. Functional magnetic resonance imaging will be acquired during baseline, week 15, and week 27 visits for patients with compatible devices that meet the inclusion criteria.

Inclusion Criteria:

1. Male or female patients who had previously undergone bilateral STN deep brain stimulation implantation
2. Age >18 years old
3. Stable medication regimen for at least 3 months.
4. Patient informed and able to give written consent
5. Able to comply with all testing, follow-ups and study appointments and protocols

Exclusion Criteria:

1. History of epilepsy or seizure
2. History of dementia
3. History of major substance abuse