Heatwaves and sleep, sleep and development, mood, neurological disorders and much more!

Abstract

Dear members of the ESRS, Dear readers of Journal of Sleep Research (JSR), Let me welcome you to the second issue of JSR in 2023. It may be a bit premature to talk about heatwaves and sleep at this time of the year, but summer will be coming, and after last year's heatwaves a work group of the insomnia network thought it worthwhile to summarize some recommendations how to deal with sleep problems during heatwaves. Altena et al. (2023) summarize some basic knowledge about why this topic is important (climate change!), how heatwaves can disturb sleep, especially in vulnerable populations, and how we can deal with these problems. Many suggestions are adapted from elements of cognitive behavioural therapy for insomnia, however with more specific advice for vulnerable populations like the elderly, pregnant women and those with mental disorders. Following this advice may help people to better deal with sleep problems during heatwaves, and may have general health effects concerning the limitation of the effects of heatwaves. However, given the sparse literature with respect to sleep problems affected by temperature changes, rigorous scientific methodology is needed to test the efficacy of these recommendations in the future. This seems an important task because this problem will not go away and will probably increase even in the near future. Bloch-Salisbury et al. (2023) evaluated the effect of a hearing protection device on infant sleep in the neonatal intensive care unit, a still largely neglected area of sleep medicine and sleep research. It is clear from what we know about the environmental aspects of the neonatal intensive care unit, that this is not a sleep-promoting surrounding. Thus, a circumaural hearing protection device was used in 10 premature infants who were patients in a neonatal intensive care unit. Polysomnography was used to investigate infant's sleep between three inter-feed periods throughout a period where the hearing protection device was either ON or OFF. It seemed that there was an increase in sleep from the OFF to the ON condition, and a significant decrease in sleep from the ON to the OFF condition. The inverse effects were observed for the wake state. It also turned out that active sleep was increased during the ON condition versus the OFF condition. The authors conclude from their study that their new hearing protection device may augment sleep in premature infants by reducing acute episodes of adverse noise in the intensive care unit. Wofford et al. (2023) tested whether a brief nap during an acute stressor might improve negative affect. Using a between-subjects design, stress was triggered by a modified version of the Trier Social Stress Test (a well-known stress test) in two groups of participants: nap, n = 29; and wake, n = 41. All participants were instructed that they would give a speech during the study (the topic was withheld until later) and then completed a math task. However, instead of giving a speech, after the nap the study was ended and the participants were debriefed. The authors measured negative affect, perceived stress and working memory at multiple time points before and after the nap/wake break. The break, either a nap or film-watching condition, in itself reduced perceived stress and improved working memory, but a nap did not confer additional benefits for the stress perception or working memory beyond taking a break. Interestingly, however, the nap group exhibited lower negative affect after the break than the wake group, and only the nap group displayed a reduction in negative mood compared with initial negative affect levels. This highlights, according to the authors, that naps may have effects on mood, by reducing negative affect. So it is suggested, when experiencing an acute stressor, taking a nap might be helpful to improve mood. Schinkelshoek et al. (2023) add a nice contribution with the title: Warm ears, a red flag for sleepiness? In this study, 44 patients who were designed to undergo an electroencephalogram (EEG) registration for clinical care were included in a specialized epilepsy sleep laboratory. Half of these patients underwent the EEG registration after a night of sleep deprivation versus after a normal night. As dependent measures, ear skin temperature and subjective sleepiness measured by the “Stanford Sleepiness Scale” and objective sleepiness measured by sleep onset with EEG were determined. Distal, proximal and ear skin temperature were measured repeatedly with a wireless measurement device. Ear skin temperature correlated weakly with distal skin temperature and distal-to-proximal gradient, but not with proximal skin temperature. The ear skin temperature increased significantly in a subgroup of 13 patients, between 5 min and 1 min before sleep onset, although this was also associated with a supine posture. The authors conclude that changes in ear skin temperature seem to be associated with sleep onset and the supine posture.