title: Decreased human circadian pacemaker influence after 100 days in space: a case study.
abstract: OBJECTIVE
  The objectives of this study were (1) to assess the circadian rhythms and sleep of a healthy, 42-year-old male astronaut experiencing microgravity (weightlessness) for nearly 5 months while living aboard Space Station Mir as it orbited Earth and (2) to determine the effects of prolonged space flight on the endogenous circadian pacemaker, as indicated by oral temperature and subjective alertness rhythms, and their ramifications for sleep, alertness, and performance.
  
  
  METHODS
  For three 12- to 14-day blocks of time (spread throughout the mission), oral temperatures were taken and subjective alertness was self-rated five times per day. Sleep diaries and performance tests were also completed daily during each block.
  
  
  RESULTS
  Examination of the subject's circadian alertness and oral temperature rhythms suggested that the endogenous circadian pacemaker seemed to function quite well up to 90 days in space. Thereafter (on days 110-122), the influence of the endogenous circadian pacemaker on oral temperature and subjective alertness circadian rhythms was considerably weakened, with consequent disruptions in sleep.
  
  
  CONCLUSIONS
  Space missions lasting more than 3 months might result in diminished circadian pacemaker influence in astronauts, leading to eventual sleep problems.
authors.affiliation: Clinical Neuroscience Research Center, Department of Psychiatry, University of Pittsburgh Medical Center, Pittsburgh, PA, USA. monkth@msx.upmc.edu
authors.forename: T H
authors.initials: TH
authors.lastname: Monk
authors.forename: K S
authors.initials: KS
authors.lastname: Kennedy
authors.forename: L R
authors.initials: LR
authors.lastname: Rose
authors.forename: J M
authors.initials: JM
authors.lastname: Linenger
mesh_terms: D000328:Adult; D001683:Biological Clocks; D021081:Chronobiology Disorders / Q000175:diagnosis*; D006801:Humans; D008297:Male; D013026:Space Flight; D013997:Time Factors; D014893:Weightlessness