1. Sleep Disorders Center, Department of Neurology, Soonchunhyang University College of Medicine, Cheonan Hospital, Cheonan, South Korea
2. Department of Preventive Medicine, Soonchunhyang University College of Medicine, Cheonan, South Korea
3. Department of Neurology, Yale School of Medicine, New Haven, Connecticut, USA
4. Department of Neurology, Dongsan Medical Center, Keimyung University School of Medicine, Daegu, South Korea