The relationship between circadian and hemicircadian components of human endogenous temperature rhythms

A review of constant routine data from normative and phase-shifted subjects shows that the hemicircadian and circadian components of fitted temperature data are only weakly linked. In these data sets, on average, hemicircadian amplitude is one-third of the circadian amplitude and the hemicircadian minimum occurs 1.7 h earlier than the circadian minimum. However, their variations about these means are largely independent. In addition the hemicircadian component was much less affected by bright light stimuli which strongly reduced the circadian component. The circadian and hemicircadian processes represented in these temperature data correspond to those reported in studies of human sleep/wake propensity.