Effects of Evening Light Exposure on Cognitive Processing

Undoubtedly, electrical light and its constant availability is one of the greatest achievements of modern mankind. At the same time, artificial illumination of the environment is also a major challenge for our biological rhythms, particularly for circadian rhythms (i.e. rhythms spanning about one day), which also regulate our sleep-wake cycle. These rhythms are set by an internal biological clock, which is located in the so-called suprachiasmatic nuclei in mammalian brains. The most important factor that sets and entrains this clock is ambient light information, which is relayed from specialised receptors in the eye to the biological clock in the brain. This pathway ensures that the internal clock stays synchronised with the solar day. Especially blue light plays an important role in this process with the internal clock being particularly sensitive to these wavelengths, wherefore it has an arousing and awakening effect and suppresses melatonin, a hormone that otherwise supports falling asleep. In this context, smartphones, e-readers and modern TV screens have a particularly worrying feature: the light emitted by their screens has a fairly large proportion of blue light. With them, we often even take blue light into our beds thus affecting sleep, which has been shown in the past. However, we only know very little about how evening light exposure changes brain processes underlying these negative effects on sleep. Shedding light onto this is the aim of this research project. To this end, on each of two evenings participants will be exposed to one of two different light sources before going to bed, one with a high and one with a low proportion of blue light. We will then assess sleep quality and how the different light sources affect the interaction between the brain and the environment acutely during light exposure, i.e. while participants are still awake, during subsequent sleep, and whether effects of light exposure persist to the next morning. More specifically, we will study how light exposure affects the brains ability to learn and predict the occurrence of ambient stimuli as well as how it alters processing of (relevant) linguistic stimuli such as ones own name and other names or highly familiar voices (e.g. ones own parents) and unfamiliar voices. The comparison of the two light conditions will yield knowledge about how artificial light changes the interaction between our brains and the environment during wakefulness and sleep. Specifically, we expect that blue light will render processing even during sleep more wake-like, which may underlie the negative effects of artificial light on sleep quality. The knowledge gained will be highly relevant for example for recommendations regarding the optimal design of the light environment to ensure good sleep or for shift work where attention and alertness have to be maintained at times when our biological clock tells us it is time to sleep.