title: After-effect of entrainment on the period of human circadian system.
abstract: The purpose of the present study is to examine changes of the circadian period in humans during temporal isolation, where the circadian rhythm is free-running. Twelve young males each spent 22 d alone in a temporal isolation room. Rectal temperature was continuously recorded and plasma melatonin was measured on day 3 (D3) and from days 10 to 13 (D10-D13). The light intensity in the room was less than 100 lx during the waking period. The free-run period of temperature rhythm from D3 to D10 (24.75 h) was not significantly different from those of the plasma melatonin rhythm (24.63 h) and sleep-wake cycle (24.69 h). The free-run period of temperature rhythm was 24.58 h in S-1 (D2-D6), which was gradually and significantly lengthened to 24.84 h in S-2 (D6-D10), 25.16 h in S-3 (D12-D16), and 25.18 h in S-4 (D18-D22). The free-run period of rectal temperature rhythm was steadily lengthened throughout the isolation period, which was probably due to the after-effect of previous entrainment to 24-h time cues.
authors.affiliation: Department of Physiology, Hokkaido University School of Medicine, Sapporo, 060-8638, Japan.
authors.forename: T
authors.initials: T
authors.lastname: Endo
authors.forename: S
authors.initials: S
authors.lastname: Honma
authors.forename: S
authors.initials: S
authors.lastname: Hashimoto
authors.forename: K i
authors.initials: Ki
authors.lastname: Honma
mesh_terms: D000328:Adult; D001831:Body Temperature / Q000502:physiology; D002940:Circadian Rhythm / Q000502:physiology*; D006801:Humans; D008029:Lighting; D008297:Male; D008550:Melatonin / Q000097:blood; D009043:Motor Activity / Q000502:physiology; D012146:Rest / Q000502:physiology; D012934:Social Isolation; D013997:Time Factors; D014851:Wakefulness / Q000502:physiology
chemical_list: D008550:Melatonin