The effects of insufficient sleep and adequate sleep on cognitive function in healthy adults

Abstract

Study objectives: Although sleep affects a range of waking behaviors, the majority of studies have focused on sleep loss with relatively little attention on sustained periods of adequate sleep. The goal of this study was to use an experimental design to examine the effect of both of these sleep patterns on cognitive performance in healthy adults.

Methods: This study used a randomized crossover design. Participants who regularly slept 7-9 hours/night completed two 6-week intervention conditions, adequate sleep (maintenance of habitual bed/wake times) and insufficient sleep (reduction in sleep of 1.5 hours relative to adequate sleep), separated by a 2-6weeks (median=43days) washout period. Cognitive functioning was evaluated at baseline and endpoint of each intervention using the NIH Toolbox Cognition Battery. General linear models contrasted scores following each condition to the baseline of the first condition; the baseline of the second condition was included to evaluate practice effects.

Results: Sixty-five participants (age 35.9 ± 4.9years, 89% women, 52% non-White race/ethnicity) completed study procedures. There was improvement in performance on the List Sorting Working Memory task after the adequate sleep condition that exceeded practice effects. Cognitive performance after insufficient sleep did not reach the level expected with practice and did not differ from baseline. A similar pattern was found on the Flanker Inhibitory Control and Attention task.

Conclusions: These findings contribute to our understanding of the complex interplay between sleep and cognition and demonstrate that consistent, stable sleep of at least 7 hours/night improves working memory and response inhibition in healthy adults.

Clinical trial registration: The manuscript reports on data from two clinical trials: Impact of Sleep Restriction on Performance in Adults (URL: https://clinicaltrials.gov/ct2/show/NCT02960776, ID Number: NCT02960776) and Impact of Sleep Restriction in Women (URL: https://clinicaltrials.gov/ct2/show/NCT02835261, ID Number: NCT02835261).

Keywords: Adequate sleep; Cognition; Insufficient sleep; Sleep restriction; Stable sleep; Working memory.

Figure 1.. Study design.

Participants underwent study measures, including cognitive testing, at the baseline of the first condition (B1) before being randomized into a 6-week intervention of either adequate sleep or insufficient sleep. Assignment to study condition was counter balanced. Following completion of a study condition, participants were evaluated with the same cognitive battery. Following a 6-week washout period, another assessment was conducted at the baseline of the second condition (B2) and then after 6 weeks of either adequate sleep or insufficient sleep. Models of cognitive test performance following insufficient sleep, adequate sleep, and at B2 compared with B1 performance permitted the evaluation of the effects of the intervention condition with respect to the expected change due to practice effects or repeated exposure to the cognitive instrumentation.

Figure 2.. Differences in performance on the List Sorting Working Memory Test across the four study visits.

The improved score from the baseline of the first condition (B1) to the baseline of the second condition (B2) indicates a practice effect. Following the adequate sleep condition, participants showed greater improvement than what would be expected with practice. However, following the insufficient sleep condition, participants did not improve as much as would be expected with practice; there were no statistical differences between B1 and performance following the insufficient sleep condition. Values plotted are means (SE) derived from the repeated measures analysis of variance models.