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Abstract
Although sleep restriction is associated with decrements in daytime alertness and neurobehavioural performance, there are considerable inter-individual differences in the degree of impairment. This study examined the effects of short-term sleep restriction on neurobehavioural performance and sleepiness, and the associations between individual differences in impairments and circadian rhythm phase. Healthy adults (n = 43; 22 M) aged 22.5 ± 3.1 (mean ± SD) years maintained a regular 8:16 h sleep:wake routine for at least three weeks prior to laboratory admission. Sleep opportunity was restricted to 5 hours time-in-bed at home the night before admission and 3 hours time-in-bed in the laboratory, aligned by wake time. Hourly saliva samples were collected from 5.5 h before until 5 h after the pre-laboratory scheduled bedtime to assess dim light melatonin onset (DLMO) as a marker of circadian phase. Participants completed a 10-min auditory Psychomotor Vigilance Task (PVT), the Karolinska Sleepiness Scale (KSS) and had slow eye movements (SEM) measured by electrooculography two hours after waking. We observed substantial inter-individual variability in neurobehavioural performance, particularly in the number of PVT lapses. Increased PVT lapses (r = -0.468, p < 0.01), greater sleepiness (r = 0.510, p < 0.0001), and more slow eye movements (r = 0.375, p = 0.022) were significantly associated with later DLMO, consistent with participants waking at an earlier circadian phase. When the difference between DLMO and sleep onset was less than 2 hours, individuals were significantly more likely to have at least three attentional lapses the following morning. This study demonstrates that the phase of an individual’s circadian system is an important variable in predicting the degree of neurobehavioural performance impairment in the hours after waking following sleep restriction, and confirms that other factors influencing performance decrements require further investigation.
Highlights
Sleep restriction impairs waking alertness, mood and neurobehavioural performance, including sustained attention, cognitive speed, cognitive accuracy and reaction time [1,2,3], in a dose-dependent [1, 4] and cumulative manner [1, 5]
The proportion of 30-second EOG epochs containing slow eye movements (SEM) during the 3-minute Karolinska Drowsiness Test (KDT) ranged from 0% to 83% with an average of 24.86 ± 31.16% (n = 37)
The two groups did not differ in sleep onset time (t (29.4) = -1.31, p > 0.05), individuals in the no lapse group had significantly earlier circadian phase as determined by the clock time of dim light melatonin onset (DLMO) (t(24.3) = -3.52, p < 0.01)
Summary
Sleep restriction impairs waking alertness, mood and neurobehavioural performance, including sustained attention, cognitive speed, cognitive accuracy and reaction time [1,2,3], in a dose-dependent [1, 4] and cumulative manner [1, 5]. Inter-individual differences in impairment to sleep loss increase with higher sleep pressure [9], and are consistently observed within subjects across multiple exposures and across multiple neurobehavioural domains including sustained attention, selective attention, serial reaction time and scales for global vigor [2, 7, 12, 13]. These studies indicate that there are systematic trait-like differences in response to sleep loss. There appears to be variation in the amount of sleep required by an individual to maintain performance [18, 19], including reports of higher sleep need in women than men [20,21,22], others [23] indicate that individual differences in performance impairment following sleep loss are not determined by basal sleep need
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