Circadian regulation of subjective alertness in morning and evening ‘types’

A sample of 144 Ss (Experiment 1) and 30 Ss (Experiment 2) was administered the Morningness Eveningness Questionnaire (MEQ). For each typology (morning-, intermediate- and evening-type) scores were computed for the following three dimensions: time of day of maximum efficiency, sleep onset time, awakening time. Statistical analysis (ANOVA with two variables: typologies × percentage values for the three dimensions) showed, in both experiments, a different percentage distribution for the three dimensions of the different circadian typologies. The dimension that differentiates morning-evening typologies is basically the first dimension (time of maximum efficiency). In Experiment 2, body temperature and subjective alertness readings were collected every 2 hr from 8 a.m. to 10 p.m. The results seem to support the hypothesis that the first dimension is mainly representative of the endogenous circadian pacemaker (ECP) while the second and third are more representative of the sleep/wake cycle (SWC). The results are discussed in relation to current hypotheses on the mechanisms underlying circadian regulation of subjective alertness.