Rapid eye movement (REM) sleep behavior disorder (RBD) is a sleep disorder in which you act out dreams during REM sleep. Sleep disturbances are very common in RBD, where they negatively impact patients' quality of life and safety. One of the known causes of sleep disturbance is the impairment of the "circadian rhythm", or the human sleep/wake cycle. The purpose of this study is to examine the role of disruption of the circadian rhythm in the development of RBD.

Inclusion Criteria:

1. Diagnosis of RBD as assessed by the International Classification of Sleep Disorders (ICDS) diagnostic criteria within 3 years
2. 40 yrs of age

Exclusion Criteria:

1. Other significant neurological disorder
2. Untreated significant sleep apnea and/or current sleep apnea symptoms as assessed by the clinical investigator
3. Co-existent restless legs syndrome (RLS), as assessed by the ICDS diagnostic criteria for RLS
4. Cognitive impairment as determined by the Montreal Cognitive Assessment (MoCA) score of ≤ 23
5. Presence of depression defined as the Beck Depression Inventory (BDI) score >20
6. Use of tricyclic antidepressants, MAO inhibitors or selective serotonin reuptake inhibitors since they may induce/worsen RBD, unless on a stable dose of medication for at least 8 weeks
7. Use of medications known to affect melatonin secretion, such as lithium, α- and β-adrenergic antagonists
8. Shift work, currently or within the prior 3 months
9. Travel through ≥ 2 time zones within 60 days prior to the screening

This study will involve men and women of all ethnic groups. We will recruit adults ≥ 40 years of age.

Control participants will be age- (±5 years) and gender-matched to participants with RBD, have no diagnosis of RBD, and meet all other inclusion/inclusion criteria as the RBD group.