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Summary: Three groups of young, normal sleepers were selected as morning types (MTs).1 evening types (ETs), and neither types (NTs) as determined by the Horne and Ostberg questionnaire. Sleep and rectal temperatures were recorded under three conditions: baseline nights (Cond. 1), sleep on the recovery day after 1 night of sleep deprivation (Cond. 2), and sleep on the recovery night after I night and 1 day of sleep deprivation (Cond. 3). During Conds. 1 and 3, when sleep schedules were self-determined, sleep structure and body temperature were similar in MTs, and ETs, and NTs. During Condo 2, however, MTs had poorer sleep, i.e., a smaller percentage of REM sleep and more awakenings, than ETs. This difference can be related to the evolution of temperature during Condo 2; i.e., a temperature increase in the MT and NT and a decrease in the ET. Key Words: Human sleep--Morning type-Evening type-Sleep deprivation-Temperature evolution.Classifying individuals as morning types (MTs), evening types (ETs), and neither types (NTs) is based, in addition to everyday observations, on (a) reported sleep schedules (1), (b) subjectively assessed arousal (2,3), and (c) the time of temperature peak (1). Other circadian variables, such as the excretion of catecholamine (norepinephrine) (2), are not significant indicators of type.All studies differentiating MTs from ETs have utilized diurnal measurements. As far as we know, only Webb and Bonnet (4) have studied nocturnal sleep. However, they clearly differentiated only two groups, MTs and ETs, and studied these two groups only in relation to their sleep schedules and the subjective quality of their sleep. Except for the work of Breithaupt et al. (5), few studies have been devoted to the influence of MT/ET typology on sleep when sleep is delayed.The present study investigates the internal sleep structure of MTs and ETs in relation to the temporal evolution of body temperature. METHODSNineteen healthy young subjects (aged from 20 to 26 years) selected by means of a questionnaire (1) participated as paid volunteers. All subjects were satisfied with both their sleep and diurnal vigilance and had agreed to keep a 2-week sleep log.

The present study compares the effects on sleep and the subsequent period of wakefulness of delaying bedtime of 2 h or advancing rising time by 2 h in subjects clearly differentiated by morningness or eveningness in their circadian rhythms. Twelve young healthy good sleepers, six morning types (MT) and six evening types (ET), were selected. The data obtained from the second 24 h (night and day) with delayed bedtime (DB) and advanced rising time (AR) were compared with those obtained in the reference condition (R) with normal sleep schedules. Sleep was recorded polygraphically and rectal temperature was continuously monitored during the nights and during the day following the second night of each condition. Subjective estimations of alertness, performance tasks and urinary steroids were analysed. Early rising appeared to be more disturbing than a late bedtime. The second shortened night showed fewer characteristics of recovery sleep in AR than in DB. The decrease in self rated alertness was a function both of the type of condition (DB or AR) and of the morning-evening typology of the subject. The largest decrease was observed in AR and in the ET subjects. AR also resulted in the most pronounced decrease in performance tasks and in an increase in urinary 17 ketosteroids without changes in the 17 hydroxy-corticosteroids. The effects on rectal temperature were limited to short periods after bedtime in DB and rising time in AR.