The study was stopped early due to insufficient staff to continue EEG data collection and analysis following the departure of key study personnel.

This study evaluates the role of subthalamic nucleus (STN) stimulation location and frequency on a range of cognitive processes in Parkinson's patients who have undergone Deep Brain Stimulation (DBS).

Pre- and post- DBS implantation brain scans will be reviewed by the study team to see if patients' DBS settings can be personalized. If so, study subjects will undergo adjustments to their DBS settings and be asked to perform cognitive tests. Some patients will be asked to come back for a second visit for brain scans.

Inclusion Criteria:

1. Between 40 and 70 years of age,
2. Ability to provide informed consent,
3. Clinical diagnosis of idiopathic Parkinson disease (PD) by a movement disorders neurologist,
4. Disease duration of at least 4 years,
5. Treated with bilateral STN DBS for at least 3 months prior to study enrollment.

Exclusion Criteria:

1. History of prior neurosurgical intervention for PD (e.g., DBS, thalamotomy, pallidotomy)

2. History of other central nervous system disease (excluding migraine),

3. Presence of active psychiatric symptoms meeting Diagnostic and Statistical Manual of Mental Disorders-4th Edition (DSM-IV) criteria for Axis-I disorder on formal psychiatric evaluation, with the exception of mild depression (Beck Depression Inventory-2 score below 19),

4. Cognitive impairment meeting Diagnostic and Statistical Manual of Mental Disorders-4th Edition (DSM-IV) criteria for dementia on formal neuropsychological evaluation,

5. Current alcohol or substance abuse,

6. Lack of fluency in English which would invalidate cognitive testing,

7. Hearing or visual impairment precluding cognitive testing.

   Exclusion criteria for Day 2 procedures:

8. Inability to safely undergo MRI procedure (i.e., metal objects like prostheses, pacemakers)

Adverse event data were collected for 2-3 days, depending on the number of study sessions, with monitoring by Clinical Research Unit (CRU) nursing staff and the research team. Participants were assessed for safety and well-being after each change in stimulation parameters during EEG recording and fMRI sessions as well as by telephone one day after their final study session.

Limitations of this trial include early termination due to a lack of eligible patients which led to a reduced sample size and limited data collection. This constraint impacted the statistical power and the ability to conduct complete analyses as initially planned. Additionally, technical limitations related to EEG data collection and analysis emerged, as key personnel responsible for EEG recording and data processing were unavailable.