Imaging Biomarkers in Parkinson s Disease

Background: \- Parkinson s disease (PD) causes slow movement, stiffness, and tremor. It results from the loss of a brain chemical called dopamine. PD gets worse over time, but researchers do not fully understand why the brain cells that produce dopamine stop working or die in people with PD. This study will use different ways of imaging the brain and brain chemicals to look at PD. It will compare brain imaging in people who definitely have PD to people who might have PD and to people without signs of PD. It will provide more information how the brain in people with PD changes over time. Objectives: \- To understand the changes that occur in the brains of people with Parkinson s disease. Eligibility: * Individuals at least 18 years of age who have definite or possible Parkinson s disease. * Healthy volunteers at least 18 years of age. Design: * Participants will have a screening visit with a physical exam and medical history. * Participants will visit the National Institutes of Health Clinical Center every 18 month or 3 years for up to 9 years. There will be up to 6 total visits. Most visits will last 5 to 6 hours a day for 1 to 3 days. Some or all of the following tests will be performed at each visit: * Magnetic resonance imaging to take pictures of the brain. Some of these tests will be done at rest. Others will require participants to perform an activity during the scan. * Medication withdrawal for 12 hours overnight for people taking PD medications. This may be done before some scans. Participants who feel unwell when they stop taking medications will be allowed to start taking them again. * Participants will continue with the follow up visits until the end of the study.