Additional Study Information: We are doing this research study to find out how different amounts of sleep restriction affect yourbody's ability to generate heat. This study will determine the effects of partial sleep restriction (PSR) (4 h in bed) and total sleep deprivation (TSD) (0 h in bed) compared to a full night of habitual sleep (HS)(8 h in bed) on brown adipiose tissue (BAT) activation. The HS condition will last 3 days and will take place at the participants home. The PSR phase will last 3 days and the TSD phase will last 1 day. Participants will become inpatients at Columbia for the PSR and TSD phases. All participants will begin the study with the 3-day HS phase that will be followed by the PSR. This will be followed by a 2-week wash-out period in which the participant will sleep on hisregular schedule. Following this 2-week period, participants will repeat the 3-day HS condition athome followed by the TSD. After waking up from the last night of the first 3-day HS period, the last night of the PSR period, and in the morning after the TSD period, participants will be taken to NYULMC for the testing of BAT activation. They will be scanned using established imaging techniques.