REM sleep behavior disorder (RBD) is when people act out their dreams while asleep. Some with RBD may later develop Parkinson's Disease or similar brain conditions. This study, called the North American Prodromal Synucleinopathy Consortium Stage 2 (NAPS2), is looking for people with RBD and healthy individuals (controls) to prepare for a future study aiming to protect the brain from these conditions. Participants will have clinical assessments, give blood samples, and have brain scans. The RBD group will also have two overnight sleep studies. This data may help find early signs of these diseases and create a list of potential participants for future trials. Procedures for the RBD group include clinical assessments, questionnaires, blood draw, brain scans (MRI and DaTscan), sleep study (polysomnogram), and optional spinal tap. The control group will have similar procedures without the sleep study or DaTscan.

• Participants must be older than 18 and capable of giving consent.
• RBD participants must not have been diagnosed with Parkinson's or related conditions unless previously involved in NAPS1.
• Participation involves various testing, including MRI and blood draws.