Sleep schedules and peak times of oral temperature and alertness in morning and evening ‘types’

Abstract

The relation between circadian variables (oral temperature and subjective alertness) and sleep-awake schedules was explored as a function of a subjective preference index (Home and Ostberg 1976) which classifies subjects as ’morning’ or ‘evening’ type. Measurements of oral temperature and self-assessed alertness were obtained every 3 hours from rising time to bedtime over a 2 week period in 49 medical students. Sleep logs were kept by the students during the same period. Sleep schedules and alertness peak time, as well as the relative temporal location of alertness peak time and temperature peak time, differed in relation to the Home and Ostberg index. These results suggest that in normal conditions the coupling between temperature circadian rhythm and sleep-awake cycle differs in morning types and evening types.