Blood Pressure Effects on Cognition and Brain Blood Flow in PD

Inclusion Criteria: 1. Diagnosis of idiopathic Parkinson Disease using the Movement Disorders Society (MDS) Clinical Diagnostic Criteria 2. Age at least 50 years old 3. Hoehn \& Yahr (H\&Y) stages I-III (early to moderate-stage PD; able to walk without assistance 4. Proficiency in the English language (native English speaker level) Exclusion Criteria: 1. Any involuntary movements (i.e., tremor or dyskinesia) \> 3 cm in amplitude (ok if movements are treated with medication), since the motion artifact could interfere with blood pressure monitor data collection 2. Dementia (including PD dementia) 3. History of deep brain stimulation (DBS) surgery 4. Any current unstable, active medical problem, e.g. decompensated heart failure, liver failure, pneumonia, etc. 5. Moderate or severe carotid artery stenosis (according to North American Symptomatic Carotid Endarterectomy Trial (NASCET) criteria 6. History of cerebral infarction or hemorrhage 7. Uncontrolled diabetes or any other systemic disease causing autonomic failure 8. Syncope (fainting) within the past week 9. Illiteracy (unable to read) 10. Taking antihypertensive medications or alpha-adrenergic blocking medications, since these can cause hypotension (see \* below) 11. Impairment of hearing or vision that is not corrected by devices (e.g., hearing aids or glasses) 12. Currently pregnant (will be confirmed by women of child-bearing potential with a urine pregnancy test) 13. Any other condition, which, in the opinion of the investigator, could place the participant at increased risk. * Please note that persons may not participate if they are taking any of the following: * medications to treat high blood pressure (called "antihypertensives") such as clonidine (Catapres), hydralazine, verapamil, diltiazem (Cartia), or medications ending in "-olol", "-artan", or "-pril") * diuretics (also called "water pills") such as furosemide (Lasix), bumetanide (Bumex), hydrochlorothiazide (HCTZ; Microzide), or spironolactone (Aldactone) * medications for enlarged prostate such as prazosin (Minipress), terazosin, doxazosin (Cardura), alfuzosin (Uroxatral), or tamsulosin (Flomax) If persons are taking these medications and would like to participate in the study, they will be advised to discuss whether they may discontinue these medications for 48 hours before the study visit with their prescribing doctor.