Circadian Rhythms and Sleep-Wake Cycles in Parkinson's Disease

Inclusion Criteria: 1. Diagnosis of idiopathic PD as defined by the United Kingdom PD Society Brain Bank Criteria; 2. PD Hoehn and Yahr stage 2-4; 3. Pittsburgh Sleep Quality Index (PSQI) score \>5 in group 1, and ≤5 in group 2; 4. Epworth Sleepiness Scale (ESS) score ≥10 in group 1, and \<10 in group 2; Control participants will be matched for gender and age with PD participants. Exclusion Criteria: 1. Atypical or secondary forms of Parkinsonism; 2. Cognitive impairment as determined by the Mini-Mental State Examination (MMSE) score of ≤ 26; 3. Presence of depression defined as the Beck Depression Inventory (BDI) score \>14; 4. Use of hypno-sedative drugs for sleep or stimulants; participants will be allowed to taper these drugs and will become eligible at least 4 weeks after the taper is completed; 5. Use of SSRIs / SNRIs antidepressants, unless the participant has been on a stable dose for at least 3 months prior to the screening; 6. Use of medications known to affect melatonin secretion; 7. Unstable/serious medical illness.