AN APPROACH TO STUDYING CIRCADIAN-RHYTHMS OF ADOLESCENT HUMANS

The ''long nights'' protocol was designed to evaluate sleep processes and circadian rhythm parameters in young humans. A total of 19 childre n (10 boys, ages 11.2 to 14.1 years [mean = 12.7 +/- 1.0], and 9 girls , ages 12.2 to 14.4 years [mean = 13.1 +/- 0.7]) took part in the stud y. Sleep/wake initially was assessed at home using actigraphy and diar y for 1 week on each child's self-selected schedule followed by an 8-n ight fixed light-dark (LD) condition, while sleeping from 22:00 to 08: 00 h and wearing an eye mask to exclude as much light as possible. Pha se measurements included 4-night mean actigraphically estimated sleep onset and offset as well as 1-night dim light salivary melatonin onset (DLSMO) phase at the end of each condition. Subjects then Lived in th e laboratory for 6 consecutive cycles: Day 1 LD = 14:10 h, Lights out 22:00 to 08:00 h; Days 2-4 LD = 6:18 h, lights out 18:00 to 12:00 h; D ays 5-6 = constant routine in continuous dim Light (about 20 lux); Nig ht 6 = 14 h recovery sleep. Phase markers (sleep onset, sleep offset, DLSMO) were significantly less dispersed after the fixed LD as compare d to the self-selected condition, indicating efficacy of the LD protoc ol. Phase markers were correlated at the self-selected assessment (sle ep onset vs. sleep offset r = .72; DLSMO vs. sleep onset r = .82; DLSM O vs. sleep offset r = .76) but not on the fixed schedule, probably du e to restricted range. The constant routine provided additional phase markers, melatonin offset and midphase. Offset phase of melatonin secr etion was significantly correlated with age (r = .62) and Tanner stage (r = .62). In conclusion, these preliminary data indicate a relations hip between adolescent development and circadian phase. Thus, the long nights protocol is a feasible way in which to assess circadian parame ters in young humans as well as to examine intrinsic sleep processes.