Reconfigurations in brain networks upon awakening from slow wave sleep: Interventions and implications in neural communication

Sleep inertia is the brief period of impaired alertness and performance experienced immediately after waking. While the neurobehavioral symptoms of sleep inertia are well-described, less is known about the neural mechanisms underlying this phenomenon. A better understanding of the neural processes during sleep inertia may offer insight into the cognitive impairments observed and the awakening process generally. We observed brain activity following abrupt awakening from slow wave sleep during the biological night. Using electroencephalography (EEG) and a network science approach, we evaluated power, clustering coefficient, and path length across frequency bands under both a control condition and a blue-enriched light intervention condition in a within-subject design. We found that under control conditions, the awakening brain is typified by an immediate reduction in global theta, alpha, and beta power. Simultaneously, we observed a decrease in the clustering coefficient and an increase in path length within the delta band. Exposure to blue-enriched light immediately after awakening ameliorated these changes, but only for clustering. Our results suggest that long-range network communication within the brain is crucial to the waking process and that the brain may prioritize these long-range connections during this transitional state. Our study highlights a novel neurophysiological signature of the awakening brain and provides a potential mechanistic explanation for the effect of light in improving performance after waking.

Effects of post short nap sleep inertia on cognitive and psychomotor task performance

Introduction: Sleep inertia, a detrimental effect of daytime nap, may affect cognitive functions following awakening. The present study aimed to assess the effects of sleep inertia on cognitive and psychomotor tasks following short nap of 30 min taken in the afternoon hours, a realistic probability in the aerospace operational environment. Material and Methods: In a repetitive measure design, 30 healthy male volunteers having adequate sleep the previous night, were tested for changes in cognitive and psychomotor performance following 30 min of nap after lunch at the Sleep-cum-Group confinement lab. Post nap longitudinal testing for dual task (DT) test and Stroop test was carried out in periodic intervals for 40 min. DT response time (DTRT), DT lag error (DTLE), DT correct clicks (DTCC) and response time difference (Stroop Effect [SE]) were analyzed as performance measures. Results: There was a significant increase in DTRT (χ2 =11.13, P = 0.011) in the post-nap period as compared to pre-nap baseline values. No significant changes were observed in other parameters vis DTLE, DTCC, and SE. Post-hoc analysis revealed that the increase of DTRT was significant at 6 min post-nap session; following which the changes were not statistically significant. Conclusion: Sleep inertia was found to affect speed component of the task rather than accuracy in a post-nap period of 30 min. The effect was significant at 6 min following awakening and after that, the effects got dissipated. Although nap can be an effective strategy for sleep-alertness management, the effects of sleep inertia have to be borne in mind, especially during sustained military operations.

A novel bedtime pulsatile-release caffeine formula ameliorates sleep inertia symptoms immediately upon awakening

Sleep inertia is a disabling state of grogginess and impaired vigilance immediately upon awakening. The adenosine receptor antagonist, caffeine, is widely used to reduce sleep inertia symptoms, yet the initial, most severe impairments are hardly alleviated by post-awakening caffeine intake. To ameliorate this disabling state more potently, we developed an innovative, delayed, pulsatile-release caffeine formulation targeting an efficacious dose briefly before planned awakening. We comprehensively tested this formulation in two separate studies. First, we established the in vivo caffeine release profile in 10 young men. Subsequently, we investigated in placebo-controlled, double-blind, cross-over fashion the formulation’s ability to improve sleep inertia in 22 sleep-restricted volunteers. Following oral administration of 160 mg caffeine at 22:30, we kept volunteers awake until 03:00, to increase sleep inertia symptoms upon scheduled awakening at 07:00. Immediately upon awakening, we quantified subjective state, psychomotor vigilance, cognitive performance, and followed the evolution of the cortisol awakening response. We also recorded standard polysomnography during nocturnal sleep and a 1-h nap opportunity at 08:00. Compared to placebo, the engineered caffeine formula accelerated the reaction time on the psychomotor vigilance task, increased positive and reduced negative affect scores, improved sleep inertia ratings, prolonged the cortisol awakening response, and delayed nap sleep latency one hour after scheduled awakening. Based on these findings, we conclude that this novel, pulsatile-release caffeine formulation facilitates the sleep-to-wake transition in sleep-restricted healthy adults. We propose that individuals suffering from disabling sleep inertia may benefit from this innovative approach.Trials registration: NCT04975360.

Effects of a Short Daytime Nap on the Cognitive Performance: A Systematic Review and Meta-Analysis

Background: Napping in the workplace is under debate, with interesting results on work efficiency and well-being of workers. In this systematic review and meta-analysis, we aimed to assess the benefits of a short daytime nap on cognitive performance. Methods: PubMed, Cochrane Library, ScienceDirect and PsycInfo databases were searched until 19 August 2021. Cognitive performance in working-aged adults, both before and following a daytime nap or under control conditions (no nap), was analysed by time and by type of cognitive function (alertness, executive function and memory). Results: We included 11 studies (all in laboratory conditions including one with a subgroup in working conditions) for a total of 381 participants. Mean duration of nap was 55.4 ± 29.4 min. Overall cognitive performance did not differ at baseline (t0) between groups (effect size −0.03, 95% CI −0.14 to 0.07), and improved in the nap group following the nap (t1) (0.18, 0.09 to 0.27), especially for alertness (0.29, 0.10 to 0.48). Sensitivity analyses gave similar results comparing only randomized controlled trials, and after exclusion of outliers. Whatever the model used, performance mainly improved until 120 min after nap, with conflicting results during the sleep inertia period. Early naps in the afternoon (before 1.00 p.m.) gave better cognitive performance (0.24, −0.07 to 0.34). The benefits of napping were independent of sex and age. Duration of nap and time between nap and t1 did not influence cognitive performance. Conclusions: Despite the fact that our meta-analyses included almost exclusively laboratory studies, daytime napping in the afternoon improved cognitive performance with beneficial effects of early nap. More studies in real work condition are warranted before implementing daytime napping at work as a preventive measure to improve work efficiency.

Going Beyond Position Statements: One Hospital’s Successful Initiative to Implement Napping for Night Shift Nurses

Background: Sleepiness during the night shift is associated with errors, accidents, injuries, and drowsy driving. Despite scientific evidence that supports brief naps to reduce sleepiness, and guidance documents from policy organizations, napping has not been widely implemented. Methods: An initiative to translate scientific evidence about napping was implemented in one hospital over one year. The initiative included garnering leadership support and resources, building a translation team, evaluating the evidence, responding to operational concerns, developing an implementation strategy, and then implementing and evaluating the results. Night shift nurses were surveyed pre and post nap implementation for drowsy driving, sleepiness, and work and coworker relationships. Qualitative data documented the nurses’ perceptions about napping. Findings: Three-fourths of the units that were eligible to nap successfully implemented and sustained napping. Most nurses felt refreshed by a brief nap and felt safer on the drive home, but one-fourth worried about or had sleep inertia symptoms. Drowsy driving remained unacceptably high. Conclusion: The initiative was successfully implemented on most nursing units. The mixed reaction to napping, and the unfavorable drowsy driving outcome point to the need for additional interventions to reduce sleepiness.

Sleep inertia measurement with the psychomotor vigilance task in idiopathic hypersomnia

Study Objectives Sleep inertia is a frequent and disabling symptom in idiopathic hypersomnia (IH), but poorly defined and without objective measures. The study objective was to determine whether the psychomotor vigilance task (PVT) can reliably measure sleep inertia in patients with IH or other sleep disorders (non-IH). Methods A total of 62 (51 women, mean age: 27.7 ± 9.2) patients with IH and 140 (71 women, age: 33.3 ± 12.1) with non-IH (narcolepsy = 29, non-specified hypersomnolence [NSH] = 47, obstructive sleep apnea = 39, insomnia = 25) were included. Sleep inertia and sleep drunkenness in the last month (M-sleep inertia) and on PVT day (D-sleep inertia) were assessed with three items of the Idiopathic Hypersomnia Severity Scale (IHSS), in drug-free conditions. The PVT was performed four times (07:00 pm, 07:00 am, 07:30 am, and 11:00 am) and three metrics were used: lapses, mean 1/reaction time (RT), and slowest 10% 1/RT. Results Sleep inertia was more frequent in patients with IH than non-IH (56.5% and 43.6% with severe sleep inertia in the past month, including 24% and 12% with sleep drunkenness). Lapse number increase and slowest 10% 1/RT decrease, particularly at 07:00 am and 07:30 am, were proportional with M-sleep inertia severity, but regardless of sleep drunkenness and sleep disorders. Similar results were obtained when PVT results were compared in patients with/without D-sleep inertia, with the largest increase of the lapse number at 07:00 am and 07:30 am associated with severe sleep inertia and sleep drunkenness. Conclusions PVT is a reliable and objective measure of sleep inertia that might be useful for its characterization, management, and follow-up in patients with IH.