Objectives:To inform the debate over whether human sleep can be
chronically reduced without consequences, we conducted a doseresponse
chronic sleep restriction experiment in which waking neurobehavioral
and sleep physiological functions were monitored and compared
to those for total sleep deprivation.
Design:The chronic sleep restriction experiment involved randomization
to one of three sleep doses (4 h, 6 h, or 8 h time in bed per night), which
were maintained for 14 consecutive days. The total sleep deprivation
experiment involved 3 nights without sleep (0 h time in bed). Each study
also involved 3 baseline (pre-deprivation) days and 3 recovery days.
Setting:Both experiments were conducted under standardized laboratory
conditions with continuous behavioral, physiological and medical monitoring.
Participants: A total of n = 48 healthy adults (ages 21–38) participated in
Interventions:Nocturnal sleep periods were restricted to 8 h, 6 h or 4 h
per day for 14 days, or to 0 h for 3 days. All other sleep was prohibited.
Results:Chronic restriction of sleep periods to 4 h or 6 h per night over
14 consecutive days resulted in significant cumulative, dose-dependent
deficits in cognitive performance on all tasks. Subjective sleepiness ratings
showed an acute response to sleep restriction but only small further
increases on subsequent days, and did not significantly differentiate the 6
h and 4 h conditions. Polysomnographic variables and δ power in the non-
REM sleep EEG—a putative marker of sleep homeostasis—displayed an
acute response to sleep restriction with negligible further changes across
the 14 restricted nights. Comparison of chronic sleep restriction to total
sleep deprivation showed that the latter resulted in disproportionately
large waking neurobehavioral and sleep δ power responses relative to
how much sleep was lost. A statistical model revealed that, regardless of
the mode of sleep deprivation, lapses in behavioral alertness were nearlinearly
related to the cumulative duration of wakefulness in excess of
15.84 h (s.e. 0.73 h).
Conclusions:Since chronic restriction of sleep to 6 h or less per night
produced cognitive performance deficits equivalent to up to 2 nights of
total sleep deprivation, it appears that even relatively moderate sleep
restriction can seriously impair waking neurobehavioral functions in
healthy adults. Sleepiness ratings suggest that subjects were largely
unaware of these increasing cognitive deficits, which may explain why the
impact of chronic sleep restriction on waking cognitive functions is often
assumed to be benign. Physiological sleep responses to chronic restriction
did not mirror waking neurobehavioral responses, but cumulative
wakefulness in excess of a 15.84 h predicted performance lapses across
all four experimental conditions. This suggests that sleep debt is perhaps
best understood as resulting in additional wakefulness that has a neurobiological
“cost” which accumulates over time.