Detrimental consequences of chronic sleep restriction on cognitive function are well established in the literature. However, effects of a single night of sleep restriction remain equivocal. Therefore, we synthesized data from 44 studies to investigate effects of sleep restriction to 2-6 h sleep opportunity on sleepiness and cognition in this meta-analysis. We investigated subjective sleepiness, sustained attention, choice reaction time, cognitive throughput, working memory, and inhibitory control. Results revealed a significant increase in subjective sleepiness following one night of sleep restriction (Standardized Mean Difference (SMD) = 0.986, p < 0.001), while subjective sleepiness was not associated with sleep duration during sleep restriction (β = -0.214, p = 0.039, significance level 0.01). Sustained attention, assessed via common 10-min tasks, was impaired, as demonstrated through increased reaction times (SMD = 0.512, p < 0.001) and attentional lapses (SMD = 0.489, p < 0.001). However, the degree of impaired attention was not associated with sleep duration (ps > 0.090). We did not find significant effects on choice reaction time, cognitive throughput, working memory, or inhibitory control. Overall, results suggest that a single night of restricted sleep can increase subjective sleepiness and impair sustained attention, a cognitive function crucial for everyday tasks such as driving.

Sensor-based surveillance technology (SST) is increasingly employed in the care of people with dementia (PwD) in hospitals, nursing homes, and home care. With improved functionality and availability of SST, there will likely be a growing utilization in clinical settings. In the context of staff shortage, the expected resource-efficient safety benefits are attractive but must be critically balanced against concerns that basic ethical principles are violated. In this discussion paper, we provide a brief overview of frequently used SST and discuss ethical issues associated with their use. We identify intrusion into privacy and the complex interaction between stakeholders as the biggest challenges. Moreover, the frequent lack of decision-making capacity in PwD poses particular ethical challenges. Evidence concerning safety benefits exists mostly for the detection of patients leaving the intended area (i.e., getting up, leaving the premises) or occurring falls. The level of privacy intrusion to detect occurring falls varies widely between different sensor systems. Finally, we propose best practice recommendations for the clinical implementation of SST in the care of PwD, and we address the circumstances under which the use of sensors can be ethically justified despite the absence of legally valid informed consent.

Summary: Certain neurophysiological characteristics of sleep, in particular slow oscillations (SOs), sleep spindles, and their temporal coupling, have been well characterised and associated with human memory abilities. Delta waves, which are somewhat higher in frequency and lower in amplitude compared to SOs, and their interaction with spindles have only recently been found to play a critical role in memory processing of rodents, through a competitive interaction between SO–spindle and delta–spindle coupling. However, human studies that comprehensively address delta wave interactions with spindles and SOs, as well as their functional role for memory are still lacking. Electroencephalographic data were acquired across three naps of 33 healthy older human participants (17 female) to investigate delta–spindle coupling and the interplay between delta‐ and SO‐related activity. Additionally, we determined intra‐individual stability of coupling measures and their potential link to the ability to form novel memories in a verbal memory task. Our results revealed weaker delta–spindle compared to SO–spindle coupling. Contrary to our initial hypothesis, we found no evidence for an opposing dependency between SO‐ and delta‐related activities during non‐rapid eye movement sleep. Moreover, the ratio between SO‐ and delta‐nested spindles rather than SO–spindle and delta–spindle coupling measures by themselves predicted the ability to form novel memories best. In conclusion, our results do not confirm previous findings in rodents on competitive interactions between delta activity and SO–spindle coupling in older adults. However, they support the hypothesis that SO, delta wave, and spindle activity should be jointly considered when aiming to link sleep physiology and memory formation.

We investigated the effects of sleep duration and light intensity on effort-related cardiovascular response. We predicted that due to reduced alertness after shortened sleep duration, perceived task demand should increase which should lead to higher mental effort. Similarly, lower light intensity should also lead to lower alertness, and therefore to higher perceived task demand and therefore higher effort. Effort was operationalized as sympathetic beta-adrenergic impact on the heart and assessed through reactivity of the cardiac pre-ejection period (PEP) and systolic blood pressure (SBP). Twenty-four healthy volunteers underwent two experimental sessions, one after 5 and one after 8 h of sleep opportunity in a counterbalanced order (within-person). Experimental lighting conditions (100 lx vs. 500 lx, within-person) were applied for 15 min, and for following 5-min modified auditory Sternberg task. In line with our hypothesis, results showed a stronger SBP (and DBP) reactivity after sleep restriction (ps < 0.001), indicating higher effort exertion. Contrary to our prediction, 500 lx light led to higher PEP reactivity compared to 100 lx (p = .032). Overall, our results provide the first experimental evidence that shorter sleep duration leads to higher mental effort.

A chronotype is defined as a preference for certain behaviours (e.g., sleep and wake) to occur at specific times of day. It is therefore also temporally linked with cognitive performance across the day. In an exploratory analysis, we sought to find associations between chronotypes determined from self-reported habitual sleep timing and from salivary melatonin onset with mental effort during a 2-back working memory task. Mental effort was operationalized as sympathetic beta-adrenergic impact on the heart, which is best reflected by the cardiac pre-ejection period (PEP) and also influences systolic blood pressure (SBP). Each participant underwent two experimental sessions in the morning: once after sleeping for 8 h and once after sleeping for 5 h the night before. To determine the timing of evening melatonin onset, participants took saliva samples at hourly intervals at home in the evening, prior to their experimental sessions. Chronotypes were determined using reported sleep times from the Munich Chronotype Questionnaire and average melatonin onset during both sleep conditions. Based on this, participants were grouped into early, intermediate, or late types. Neither alertness (BF₁₀ = 0.019), perceived task demand (BF₁₀ = 0.008), nor SBP response (BF₁₀ = 0.268) were credibly impacted by sleep-time derived chronotype, while the association with PEP response (BF₁₀ = 0.631) during a cognitive challenge in the morning was inconclusive. Similarly, the timing of evening melatonin onset did not affect alertness (BF₁₀ = 0.003), perceived task demand (BF₁₀ = 0.006), or PEP or SBP response (PEP: BF₁₀ = 0.232, SBP: BF₁₀ = 0.263) during the cognitive challenge. Our data shows no impact of chronotypes on effort-related cardiovascular response during a cognitive challenge in the morning, which was scheduled according to habitual sleep times.