“Mental clocks” that lag behind the biological clocks: The effect of volitional delays of bedtime on sleep-wake regulation

sleep are determined by the endogenous mechanism of sleep-wake regulation. However, humans are capable to volitionally prolong (i.e. without any external influences) the wake phase of their sleep-wake cycle to early night hours. We hypothesized that the conscious behaviors mostly known under the terms "bedtime procrastination" and "mind-bedtime procrastination" can compete with the biological sleep-wake regulator for setting bedtimes on weekdays and/or weekends and thus this behavior can contribute to the delay of sleep relative to the bedtime signal from this regulator. University students (5375 in total) were grouped in accord with their earlier or later weekday and weekend bedtimes. To test the hypothesis, the group-averaged sleep times were calculated and simulated. Near 8% of students reported later weekday than weekend bedtimes. The simulations of their sleep times suggested that these times cannot be explained by a model of sleep-wake regulator without the additional assumption of bedtime delay caused by the volitional missing the bedtime signal from this regulator (i.e. this missing can be a result of such volitional behavior as mind-bedtime procrastination on weekdays rather than on weekends). We concluded that the concept of two conflicting - biological and "social" - "clocks" that was introduced in this journal 20 years ago can be extended to the concept of three conflicting "clocks." Bed- and risetimes on weekdays and weekends can reflect the competition between three - biological, "social," and, additionally, "mental" - "clocks." In accord with the concept of two "conflicting clocks," weekday risetimes can be mostly determined by "social clocks" competing with the biological clocks that can be solely responsible for weekend risetimes. However, weekday and/or weekend bedtimes cannot be always set by the biological clocks. Sometimes, they are determined by the additional conflict of "mental (mind) clocks" with the biological (body) clocks. This conflict can lead to weekday sleep insufficiency and can be, in particular, explained by such kind of conscious behavior as mind-bedtime procrastination.