Three dimensions of individual variation in phase angle between sleep timing and timing of nocturnal rise of the feeling of sleepiness

Abstract

Studies of melatonin and body temperature rhythms revealed that women, younger adults, and morning-oriented types show a relatively larger phase angle between entrained circadian phase and sleep timing than men, older adults, and evening-oriented types, respectively. However, none of these studies has been designed to compare participants representing all these three dimensions of individual variation. Since daily fluctuations in self-reported level of alertness–sleepiness closely follow the circadian rhythms of melatonin and body temperature, one can predict that a study of circadian phase characteristics of fluctuations of sleepiness shell reveals identical sex-, age-, and diurnal type-related differences in phase angle between circadian phase and sleep timing. Analysis of self-scorings of alertness–sleepiness provided by 130 healthy participants of sleep deprivation experiments confirmed this prediction. It seems that both fundamental research and field studies of sleep-deprived individuals can benefit from the evaluation of circadian phase through self-assessment of nocturnal rise of alertness–sleepiness.

Keywords:

• alertness
• sleepiness
• sleep–wake timing
• circadian phase
• gender difference
• age difference
• morning–evening preference

Additional information

Funding

Funding. The experimental study was supported by the Russian Foundation for Basic Research [grant number 07-06-00263-a], [grant number 10-06-00114-a], and [grant number 13-06-00042-a]; and the Russian Foundation for Humanities [grant number 06-06-00375-a] and [grant number 12-06-18001-e]. I am indebted to Dr. Evgeniy Verevkin and Olga Donskaya for their help in collecting, analyzing, and simulating data on KSS scorings.