Evidence that Homeostatic Sleep Regulation Depends on Ambient Illuminance Levels

Abstract

We examined whether the ambient illuminance during extended wakefulness modulates the homeostatic increase in human deep sleep [i.e. slow wave sleep (SWS) and electroencephalographic (EEG) slow-wave activity (SWA)] in healthy young and older volunteers. Thirty-eight young and older participants underwent 40 hours of extended wakefulness [i.e. sleep deprivation (SD)] once under dim light (DL: 8 lux, 2800K), and once under either white light (WL: 250 lux, 2800K) or blue-enriched white light (BL: 250 lux, 9000K) exposure. Subjective sleepiness was assessed hourly and polysomnography was quantified during the baseline night prior to the 40-h SD and during the subsequent recovery night. Both the young and older participants responded with a higher homeostatic sleep response to 40-h SD after WL and BL than after DL. This was indexed by a significantly faster intra-night accumulation of SWS and a significantly higher response in relative EEG SWA during the recovery night after WL and BL than after DL for both age groups. No significant differences were observed between the WL and BL condition for these two particular SWS and SWA measures. Subjective sleepiness ratings during the 40-h SD were significantly reduced under both WL and BL compared to DL, but were not significantly associated with markers of sleep homeostasis in both age groups. Our data indicate that not only the duration of prior wakefulness, but also the experienced illuminance during wakefulness affects homeostatic sleep regulation in humans. Thus, working extended hours under low illuminance may negatively impact subsequent sleep intensity in humans.

Bright Light During Wakefulness Improves Sleep Quality in Healthy Men: A Forced Desynchrony Study Under Dim and Bright Light (III)

“…Spontaneous wake-up times could not be measured in this FD protocol; nevertheless, we argue that data presented here suggest that BL exposure increases sleep pressure buildup. Light-induced increases in sleep pressure have been determined before in both humans (Cajochen et al, 2019) and animals (Altimus et al, 2008; Hubbard et al, 2013; LeGates et al, 2014; Tsai et al, 2009). The delta power increase determined in data presented here coincided with light-induced improvements in subjective sleep quality, which occurred during the circadian wake maintenance phase (Figure 4).…”

“…For example, light exposure in the (late) evening decreases sleep quality (Cajochen et al, 1992;Dijk et al, 1991) since it stimulates the phase delay portion of the human phase response curve (Khalsa et al, 2003;Papantoniou et al, 2014). This effect of light on sleep mediated by the circadian system, however, does not exclude a possible direct effect of light on subsequent sleep independent of the circadian system (Cajochen et al, 2019;Horne and Walmsley, 1976;Wams et al, 2017). Our hypothesis therefore is that light effects on sleep occur independent of circadian clock phase alterations.…”