Circadian Rhythms and Homeostatic Sleep Drive and Their Effect on Reward and Cognitive Control Systems in Adolescents

P1 will study 200 adolescents ages 13-18 in a 48-h to 60-h laboratory study. Participants will monitor sleep patterns at home for 2 weeks with actigraphy and sleep diary, and will also complete fMRI measures of reward and cognitive control. This will be followed by a 48-to-60-hour laboratory visit. The laboratory session includes two nights of polysomnography (PSG) sleep studies (the second night of PSG was halted for all participants as of January 2026), separated by 28 h of an ultradian sleep/wake protocol-every 120-minutes, there will be an 80-minute period of waking, followed by a 40-minute sleep opportunity. (Prior to January 2026, participants had a 36-h ultradian sleep/wake protocol, which was then shortened to 28 hours). Participants will be in dim light conditions and temporal isolation for the first 28 h of the ultradian sleep/wake protocol. Physiological circadian measures include salivary melatonin; core body temperature (CBT); and molecular rhythms from hair follicle cells (examined in Project 3). Physiological sleep homeostatic measures include waking EEG theta power, slow-wave sleep rebound following the ultradian sleep/wake protocol (for participants enrolled prior to January 2026), and repeated sleep latency on the sleep opportunities. Behavioral tests (Reward Anti-Saccade task to index cognitive control with/without reward modulation; Psychomotor Vigilance Test) and self-reports of mood/sleepiness will be collected every 2 h. Longitudinal on-line surveys will assess substance use every 6 months for the life of the grant.