1. Sleep Medicine Center, Nanfang Hospital, Southern Medical University, Guangzhou, China
2. Center for Sleep and Circadian Neurobiology, University of Pennsylvania, Philadelphia, Pennsylvania
3. Department of Sleep, Landspitali - The National University Hospital of Iceland, Reykjavik, Iceland
4. Faculty of Medicine, University of Iceland, Reykjavik, Iceland
5. Department of Medicine, Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania
6. Department of Medicine, Corporal Michael J. Crescenz Veterans Affairs Medical Center, Philadelphia, Pennsylvania