Inclusion Criteria:  Pilot Group: Participants who enroll as part of the Pilot Group of up to10, will follow the same inclusion criteria as the Control group with the exception of matching the age and sex distribution of the DBS group. Pilot participants will be males or females between 20 and 75 years of age who do not meet criteria for clinically definite PD. Control Group: Participants who enroll as part of the Control Group will match the age and sex distributions of the DBS groups. Control participants will be males or females between 50 and 75 years of age who do not meet criteria for clinically definite PD. Pre-Surgical DBS Group: Participants with PD who have been clinically consented for bilateral STN DBS surgery will be recruited from the DBS program within the Movement Disorders Clinic at WUSM. Pre-surgical STN DBS patients will be males or females between 50 and 75 years of age who meet criteria for clinically definite PD. Post-Surgical DBS Group: Participants with PD who have had bilateral STN DBS surgery will be males or females between 50 and 75 years of age who meet criteria for clinically definite PD.  Exclusion Criteria:  Pilot Group: Exclusions include any significant past or current neurologic or psychiatric diagnosis or any other condition which could interfere with testing (e.g. severe visual loss, non-English speaking, and illiteracy) and contraindications for MRI. Control Group: Exclusions include any significant past or current neurologic or psychiatric diagnosis or any other condition which could interfere with testing (e.g. severe visual loss, non-English speaking, and illiteracy) and contraindications for MRI. Pre-Surgical DBS Group: Patients will have already passed clinical screening for neurological and psychiatric comorbidities, including dementia. From this group of potential subjects, we will also exclude those with contraindications for MRI pre-surgically, inability to tolerate off medication or off DBS states, or any other condition which could interfere with testing (e.g. severe visual loss, non-English speaking, illiteracy). Post-Surgical DBS Group: Patients will have already passed clinical screening for neurological and psychiatric comorbidities, including dementia. From this group of potential subjects, we will also exclude those with contraindications for MRI pre-surgically, clinically determined dementia manifesting after surgery, significant complications of surgery (e.g. stroke), inability to tolerate off medication or off DBS states, or any other condition which could interfere with testing (e.g. severe visual loss, non-English speaking, illiteracy).