Regulation of sleepiness: the role of the arousal system

Genetic determinants of daytime napping and effects on cardiometabolic health

Daytime napping is a common, heritable behavior, but its genetic basis and causal relationship with cardiometabolic health remain unclear. Here, we perform a genome-wide association study of self-reported daytime napping in the UK Biobank (n = 452,633) and identify 123 loci of which 61 replicate in the 23andMe research cohort (n = 541,333). Findings include missense variants in established drug targets for sleep disorders (HCRTR1, HCRTR2), genes with roles in arousal (TRPC6, PNOC), and genes suggesting an obesity-hypersomnolence pathway (PNOC, PATJ). Association signals are concordant with accelerometer-measured daytime inactivity duration and 33 loci colocalize with loci for other sleep phenotypes. Cluster analysis identifies three distinct clusters of nap-promoting mechanisms with heterogeneous associations with cardiometabolic outcomes. Mendelian randomization shows potential causal links between more frequent daytime napping and higher blood pressure and waist circumference.

Facebook use and sleep quality: Light interacts with socially induced alertness

It has been demonstrated that the use of social networking sites late at night can lead to sleep‐related problems that extend into the next day. A common explanation is that the light emitted from screens is disrupting the users’ circadian rhythms. An alternative explanation is that the social cognition inherent in the use of social networking sites is responsible. Here, the two factors were looked at together. Participants used Facebook on iPad tablets before sleep. This was done on different nights with two lighting conditions and with two levels of content. In the ‘light’ condition, blue wavelength light was manipulated so that it was either full wavelength or blue light filtered. In the ‘alertness’ condition, the personal significance of the content was changed from personally relevant to irrelevant. A modified version of the Pittsburgh Sleep Quality Index was used to measure sleep‐related problems. No evidence was found that simply filtering blue light or simply removing relevant content improved sleep quality. However, the two factors interacted. The results suggest that the light emitted from screens can affect sleep quality under some conditions but this is behaviourally irrelevant in the context of normal Facebook usage.

The psycho-sensory wake drive-a power source for power naps and other common sleep-wake phenomena: a hypothesis

Power naps are extensively practiced worldwide and there exists ample documentation of their efficacy in reversing daytime sleepiness. The source of their efficacy, however, as well as the cause and manifestation of many other common sleep-wake phenomena, cannot be entirely explained by the most commonly accepted model of sleep-wake regulation, the two-process model of Borbély, which considers the drives of the circadian and homeostatic sleep processes only. When considering the causes and manifestations of these unexplained phenomena, there appears to be evidence of a wake-promoting drive that is independent of the circadian oscillator indicated in the two-process model of sleep-wake regulation. Although this posited secondary wake drive, herein referred to as the psycho-sensory wake drive, is always active during the awake state, its strength unpredictably varies during a normal day and, therefore, cannot be incorporated into the prevalent two-process model by any current mathematical formula. However, a supplemental graphic model superimposing it on the drives of Process S and Process C can provides plausible and parsimonious explanations for many otherwise unexplainable sleep-wake phenomena and enables rational guidelines for their effective practical management.