Vanja Hommes

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

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 (<8 lux). Cognitive tasks were performed every 2 h during scheduled wakefulness, and questionnaires were administered hourly to assess subjective sleepiness, mood, and well-being. 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, well-being, and mood under mild sleep restriction.

The Melanopic Sensitivity Function Accounts for Melanopsin-Driven Responses in Mice under Diverse Lighting Conditions.

In addition to rods and cones, photoreception in mammals extends to a third retinal cell type expressing the photopigment melanopsin. The influences of this novel opsin are widespread, ranging from pupillary and circadian responses to brightness perception, yet established approaches to quantifying the biological effects of light do not adequately account for melanopsin sensitivity. We have recently proposed a novel metric, the melanopic sensitivity function (VZλ), to address this deficiency. Here, we further validate this new measure with a variety of tests based on potential barriers to its applicability identified in the literature or relating to obvious practical benefits. Using electrophysiogical approaches and pupillometry, initially in rodless+coneless mice, our data demonstrate that under a very wide range of different conditions (including switching between stimuli with highly divergent spectral content) the VZλ function provides an accurate prediction of the sensitivity of melanopsin-dependent responses. We further show that VZλ provides the best available description of the spectral sensitivity of at least one aspect of the visual response in mice with functional rods and cones: tonic firing activity in the lateral geniculate nuclei. Together, these data establish VZλ as an important new approach for light measurement with widespread practical utility.

A revision of existing Karolinska Sleepiness Scale responses to light: A melanopic perspective

A new photometric measure of light intensity that takes into account the relatively large contribution of the ipRGCs to the non-image forming (NIF) system was recently proposed. We set out to revise publications reporting on alertness scores as measured by the Karolinska Sleepiness Scale (KSS) under different light conditions in order to assess the extendibility of the equivalent-melanopic function to NIF responses in humans. The KSS response (−Δ KSS) to the different light conditions used on previous studies, preferably including a comparison to a dim light condition, was assessed. Based on the light descriptions of the different studies, the equivalent melanopic lux (m-illuminance) was calculated. The −Δ KSS was plotted against photopic-illuminance and m-illuminance, and fitted to a sigmoidal function already shown to described KSS responses to different light intensities. The root mean-squared error and r2 were used as criteria to explain the best-describing light unit measurement. Studies that compared only the influence of light under otherwise same conditions and in which participants were not totally sleep deprived were included. Our results show that the effects of light on KSS are better explained by a melanopic unit measurement than by photopic lux. The present analysis allowed for the construction of a melanopic alertness response curve. This curve needs to be validated with appropriate designs. Nonetheless, it may serve as starting point for the development of hypothesis of predictions on the relative changes in KSS under a given condition due to changes in light properties.

The effects of low-intensity narrow-band blue-light treatment compared to bright white-light treatment in seasonal affective disorder

BACKGROUND Ever since a new photoreceptor was discovered with a highest sensitivity to 470-490 nm blue light, it has been speculated that blue light has some advantages in the treatment of Seasonal Affective Disorder (SAD) over more traditional treatments. In this study we compared the effects of exposure to narrow-band blue light (BLUE) to those of broad-wavelength white light (BLT) in the treatment of SAD. METHODS In a 15-day design, 45 patients suffering from SAD completed 30-min sessions of light treatment on 5 consecutive days. 21 subjects received white-light treatment (BLT, broad-wavelength without UV, 10 000 lx, irradiance 31.7 W/m2), 24 subjects received narrow-band blue light (BLUE, 100 lx, irradiance 1.0 W/m2). All participants completed weekly questionnaires concerning mood and energy levels, and were also assessed by means of the SIGH-SAD, which is the primary outcome measure. RESULTS On day 15, SIGH-SAD ratings were significantly lower than on day 1 (BLT 73.2%, effect size 3.37; BLUE 67%, effect size 2.63), which outcomes were not statistically significant different between both conditions. LIMITATIONS Small sample size. CONCLUSIONS Light treatment is an effective treatment for SAD. The use of narrow-band blue light is equally effective as a treatment using bright white-light.