Chronic sleep restriction greatly magnifies performance decrements immediately after awakening

Abstract

Study objectives: Sleep inertia, subjectively experienced as grogginess felt upon awakening, causes cognitive performance impairments that can require up to 1.5 hr to dissipate. It is unknown, however, how chronic sleep restriction (CSR) influences the magnitude and duration of sleep inertia-related performance deficits.

Methods: Twenty-six healthy participants were enrolled in one of two in-laboratory sleep restriction protocols (one 32 day randomized control and one 38 day protocol) that separated the influence of sleep and circadian effects on performance using different "day"-lengths (20 and 42.85 hr day-lengths, respectively). The sleep opportunity per 24 hr day was the equivalent of 5.6 hr for each CSR condition and 8 hr for the Control condition. Participant's performance and subjective sleepiness were assessed within ~2 min after electroencephalogram-verified awakening and every 10 min thereafter for 70 min to evaluate performance and subjective sleepiness during sleep inertia.

Results: Performance within 2 min of awakening was ~10% worse in CSR conditions compared with Control and remained impaired across the dissipation of sleep inertia in the CSR conditions when compared with Control. These impairments in performance during sleep inertia occurred after only chronic exposure to sleep restriction and were even worse after awakenings during the biological nighttime. Interestingly, despite differences in objective performance, there were no significant differences between groups in subjective levels of sleepiness during sleep inertia.

Conclusions: CSR worsens sleep inertia, especially for awakenings during the biological night. These findings are important for individuals needing to perform tasks quickly upon awakening, particularly those who obtain less than 6 hr of sleep on a nightly basis.

Clinical trial: The study "Sleep Duration Required to Restore Performance During Chronic Sleep Restriction" was registered as a clinical trial (#NCT01581125) at clinicaltrials.gov (https://ichgcp.net/clinical-trials-registry/NCT01581125?term=NCT01581125.&rank=1).

Keywords: circadian; forced desynchrony; insufficient sleep; sleep inertia; subjective sleepiness.

© Sleep Research Society 2019. Published by Oxford University Press on behalf of the Sleep Research Society. All rights reserved. For permissions, please e-mail journals.permissions@oup.com.

Figures

Figure 1.

Performance after awakening under different sleep conditions throughout the forced desynchrony protocol. Number of correct responses on the Digit Symbol Substitution Task (DSST) under Control conditions (equivalent of 8 hr scheduled sleep per 24 hr, open symbols) and under both chronic sleep restriction (CSR) conditions (equivalent of 5.6 hr scheduled sleep per 24 hr, closed symbols) are plotted as average (± St. Err; error bars) deviation from Baseline for each individual (solid horizontal line) on y-axis and by minutes since awakening from sleep on x-axis. Data plotted below average Baseline performance levels indicate performance impairment. Asterisks indicate a significant difference using mixed model techniques and t-tests (p < 0.05) between the combined CSR conditions and Controls. Data are from n = 26 participants.

Figure 2.

Performance after awakening under different sleep conditions in the (A) first and (B) last week of each forced desynchrony protocol. Number of correct responses on the Digit Symbol Substitution Task (DSST) under Control conditions (equivalent of 8 hr scheduled sleep per 24 hr, open symbols) and under both chronic sleep restriction (CSR) conditions (equivalent of 5.6 hr scheduled sleep per 24 hr, closed symbols) are plotted as average (± St. Err; error bars) deviation from Baseline for each individual (solid horizontal line) on y-axis and by minutes since awakening from sleep on x-axis. Data plotted below average Baseline performance levels indicate performance impairment. Asterisks indicate a significant difference using mixed model techniques and t-tests (p < 0.05) between the combined CSR conditions and Controls. Data are from n = 26 participants.

Figure 3.

Performance after awakening under different sleep conditions during (A) circadian day and (B) circadian night phases during each forced desynchrony protocol. Number of correct responses on the Digit Symbol Substitution Task (DSST) under Control conditions (equivalent of 8 hr scheduled sleep per 24 hr, open symbols) and under both chronic sleep restriction (CSR) conditions (equivalent of 5.6 hr scheduled sleep per 24 hr, closed symbols) are plotted as average (± St. Err; error bars) deviation from Baseline for each individual (solid horizontal line) on y-axis and by minutes since awakening from sleep on x-axis. Data plotted below average Baseline performance levels indicate performance impairment. Asterisks indicate a significant difference using mixed model techniques and t-tests (p < 0.05) between the combined CSR conditions and Controls. Data are from n = 24 participants.

Figure 4.

Subjective sleepiness after awakening under different sleep conditions. Number selected on the Karolinska Sleepiness Scale (KSS) under Control conditions (equivalent of 8 hr scheduled sleep per 24 hr, open symbols) and under both chronic sleep restriction (CSR) conditions (equivalent of 5.6 hr scheduled sleep per 24 hr, closed symbols) are plotted as average (± St. Err; error bars) deviation from Baseline for each individual (solid horizontal line) on y-axis and by minutes since awakening from sleep on x-axis. Higher KSS scores indicate higher subjective sleepiness; note the inverted axis. Data are from n = 26 participants.