Effects of Artificial Dawn and Morning Blue Light on Daytime Cognitive Performance, Well-being, Cortisol and Melatonin Levels

Abstract

Light exposure elicits numerous effects on human physiology and behavior, such as better cognitive performance and mood. Here we investigated the role of morning light exposure as a countermeasure for impaired cognitive performance and mood under sleep restriction (SR). Seventeen participants took part of a 48h laboratory protocol, during which three different light settings (separated by 2 wks) were administered each morning after two 6-h sleep restriction nights: a blue monochromatic LED (light-emitting diode) light condition (BL; 100 lux at 470 nm for 20 min) starting 2 h after scheduled wake-up time, a dawn-simulating light (DsL) starting 30 min before and ending 20 min after scheduled wake-up time (polychromatic light gradually increasing from 0 to 250 lux), and a dim light (DL) condition for 2 h beginning upon scheduled wake time (58 lux). Cognitive tasks were performed every 2 h during scheduled wakefulness, and questionnaires were administered hourly to assess subjective sleepiness, mood, and wellbeing. Salivary melatonin and cortisol were collected throughout scheduled wakefulness in regular intervals, and the effects on melatonin were measured after only one light pulse. Following the first SR, analysis of the time course of cognitive performance during scheduled wakefulness indicated a decrease following DL, whereas it remained stable following BL and significantly improved after DsL. Cognitive performance levels during the second day after SR were not significantly affected by the different light conditions. However, after both SR nights, mood and well-being were significantly enhanced after exposure to morning DsL compared with DL and BL. Melatonin onset occurred earlier after morning BL exposure, than after morning DsL and DL, whereas salivary cortisol levels were higher at wake-up time after DsL compared with BL and DL. Our data indicate that exposure to an artificial morning dawn simulation light improves subjective well-being, mood, and cognitive performance, as compared with DL and BL, with minimal impact on circadian phase. Thus, DsL may provide an effective strategy for enhancing cognitive performance, wellbeing, and mood under mild sleep restriction.

Dawn simulation light impacts on different cognitive domains under sleep restriction

“…Our results corroborate our previous analysis that artificial morning dawn simulation light improves subjective perception of well-being and mood, as well as cognitive performance across the day under conditions of mild sleep restriction [14]. However, here we showed that the light effect on performance depends on the investigated cognitive domain, suggesting that different pathways may be implicated in this effect.…”

“…Evidence for the latter arises from studies in which daytime performance increased after 30 min from light onset [30,31], from an fMRI study in which daytime light enhanced cognitive brain activity during an oddball task [32] and from our previous analysis in which morning light exposure (dawn simulation light) increased wellbeing and enhanced performances across the day [14]. Recently, another study showed the critical role of light for cognitive brain responses in emphasizing the evidence of a cognitive role for melanopsin, which may confer a form of "photic memory" to human cognitive brain function [33].…”

“…The most likely explanation was that sleep pressure was too high after the second night of sleep restriction, and thus the morning light could not counteract its detrimental effect. For more details, referred to Gabel et al [14]. These 24-h include the first sleep restriction night (6-h) at 0 lx starting at the subject's habitual sleep time and followed by 18-h of data recording during wakefulness.…”

“…Similarly, subjective sleepiness induced by the test did not differ across the light conditions (Table 2). For detailed information on sleepiness, well-being and mood, please see [14].…”

“…In a previous study, we have shown that exposure to gradually increasing light prior to awakening can counteract sleep restriction effects on well-being and cognitive performance across the day, leading to an optimized level of alertness, which impinges on enhanced performance on specific cognitive tasks tightly related to sustained levels of attention [14].…”