The Adjustment of the Circadian Rhythm of Body Temperature to Simulated Time-Zone Transitions: A Comparison of the Effect of Using Raw Versus Unmasked Data

Deep body temperature and sleep/activity diaries data were recorded during control days and for 6 days after simulated time zone transitions of 8 h to the east (six subjects) or west (seven subjects). Circadian rhythms were assessed by cosinor analysis of both raw data (the conventional method) and purified data (corrected for the effects of sleep and activity). Analysis of raw data gives misleading information about the phase and amplitude of the rhythms due to the masking effects of the exogenous component. Use of purified data indicates that during the process of adjustment after an eastward shift (a) phase changes are more erratic than after a shift to the west; (b) no marked decrease in the amplitude of the rhythms is evident; and (c) no clear evidence exists that the circadian rhythm breaks up temporarily. The masking effect was less after the time zone transition if sleep maintenance was poor.