The study begins with 21 days of outpatient study in which the participants will be required to sleep for 10 hours each night in order to ensure they are well-rested. This will be followed by a 39-day inpatient study. The study will begin with 3 "sleep satiation" days during which all participants will be scheduled to sleep for 12 hours per night and have a 4 hour nap each afternoon. This is followed by 3 baseline days in which the participants will follow the same sleep-wake schedule they were following at home. Following this, the participant will undergo 3 weeks of chronic sleep restriction while living on a non-24-hour schedule. The participant will live on a schedule that is equivalent to 5.6 hours of sleep per 24 hours. Following these 3 weeks, the participant will be scheduled to again sleep for 10 hours per night for 10 nights.