Patient description: A 57-year old farmer was diagnosed with Parkinson's disease a year ago. He experiences slowness of movement and tremors. His past medical history is significant for hypertension and hypercholesterolemia. He lives with his wife. They have three children. He used to be active with planting and taking care of their farm animals before his diagnosis. The patient complains of shaking and slow movement. He had difficulty entering through a door, as he was frozen and needed guidance to step in. His handwriting is getting smaller. He is on Levodopa and Trihexyphenidyl. He stated his medications help with shaking and slow movement. But he still has difficulty initiating movements, stiffness and slowness in general. He is an alert and cooperative man who doesn't have any signs of dementia. He doesn't smoke or use any illicit drugs.

Clinical trial eligibility criteria: eligible ages (years): 18.0-80.0,  Parkinson for Parkinson's volunteers: 1. Male and female, age 18-80 2. Motor symptoms only on one side of the body 3. No use of dopaminergic replacement therapy or other medication related to PD  for Parkinson's volunteers: 1. Cognitive impairments that may interfere with understanding instructions as needed during the performance of the study (MMSE<23) 2. Subjects who are unable to perform arm reaching movements 3. Self-report of any condition that could affect walking 4. No fractures or skin lesions in the upper or lower limbs 5. Infectious diseases requiring contact precautions 6. Subjects with contraindications to MRI cannot participate (i.e., implanted metal including pacemakers, cerebral spinal fluid shunts, aneurysm clips, artificial heart valves, ear implants or metal/foreign objects in the eyes and those with a history of claustrophobia) 7. Pregnancy: If the possibility of pregnancy of a female participant cannot be excluded by: 1) surgical history (e.g., tubal ligation or hysterectomy) or 2) post menopausal status with a minimum of 1 year without menses, then a pregnancy test by stat serum testing must be performed on site the morning of any PET visit and the negative result is required prior to the administration or any radiopharmaceutical 8. Substance abuse within the past 2 years as it may alter neurotransmitter function 9. Active hematological, renal, pulmonary, endocrine or hepatic disorders 10. Evidence of cortical infarcts or strategically placed lacunar infarct (e.g. dorsal medial nucleus of thalamus) 11. Active cancer, metabolic encephalopathy, infection 12. Active cardiovascular disease, stroke, congestive heart failure 13. Diagnosis of MCI or dementia for healthy volunteers: 1. Male and female, age 18-80 2. Age and gender-matched to PD patients 3. No use of dopaminergic replacement therapy or other medication related to PD for healthy volunteers: 1. Cognitive impairments that may interfere with understanding instructions as needed during the performance of the study (MMSE<23) 2. Subjects who are unable to perform arm reaching movements 3. Self-report of any condition that could affect walking 4. No fractures or skin lesions in the upper or lower limbs 5. Infectious diseases requiring contact precautions 6. Diagnosis of MCI or dementia