Summary: A new study reveals the color of light can have an impact on whether we’re sleepy or fully aroused.
Light affects sleep. A study in mice published in Open Access journal PLOS Biology shows that the actual color of light matters; blue light keeps mice awake longer while green light puts them to sleep easily. An accompanying Primer provides accessible context information and discusses open questions and potential implications for “designing the lighting of the future”.
Light shining into our eyes not only mediates vision but also has critical non-image-forming functions such as the regulation of circadian rhythm, which affects sleep and other physiological processes. As humans, light generally keeps us awake, and dark makes us sleepy. For mice, which are mostly nocturnal, light is a sleep-inducer. Previous studies in mice and humans have shown that non-image-forming light perception occurs in specific photosensitive cells in the eye and involves a light sensor called melanopsin. Mice without melanopsin show a delay in their response to fall asleep when exposed to light, pointing to a critical role for melanopsin in sleep regulation.
Stuart Peirson and Russell Foster, both from Oxford University, UK, alongside colleagues from Oxford and elsewhere, investigated this further by studying sleep induction in mice exposed to colored light, i.e., light of different wave lengths. Based on the physical properties of melanopsin, which is most sensitive to blue light, the researchers predicted that blue light would be the most potent sleep inducer.
To their surprise, that was not the case. Green light, it turns out, puts mice to sleep quickly, whereas blue light actually seems to stimulate the mice, though they did fall asleep eventually. Mice lacking melanopsin were oblivious to light color, demonstrating that the protein is directing the differential response.
Both green and blue light elevated levels of the stress hormone corticosterone in the blood of exposed mice compared with mice kept in the dark, the researchers found. Corticosterone levels in response to blue light, however, were higher than levels in mice exposed to green light. When the researchers gave the mice drugs that block the effects of corticosterone, they were able to mitigate the effects of blue light; drugged mice exposed to blue light went to sleep faster than control mice that had received placebos.
Citing previous results that exposure to blue light–a predominant component of light emitted by computer and smart-phone screens–promotes arousal and wakefulness in humans as well, the researchers suggest that “despite the differences between nocturnal and diurnal species, light may play a similar alerting role in mice as has been shown in humans”. Overall, they say their work “shows the extent to which light affects our physiology and has important implications for the design and use of artificial light sources”.
In the accompanying Primer, Patrice Bourgin, from the University of Strasbourg, France, and Jeffrey Hubbard from the University of Lausanne, Switzerland, say the study “reveals that the role of color [in controlling sleep and alertness] is far more important and complex than previously thought, and is a key parameter to take into account”. The study’s results, they say, “call for a greater understanding of melanopsin-based phototransduction and tell us that color wavelength is another aspect of environmental illumination that we should consider, in addition to photon density, duration of exposure and time of day, as we move forward in designing the lighting of the future, aiming to improve human health and well-being.”
About this neuroscience research article
Funding: (RA) This work was supported by grants from the Biotechnology and Biological Sciences Research Council (BB/I021086/1) to SNP, PMN and RGF and the Wellcome Trust (098461/Z/12/Z) to RGF and SNP. The funders had no role in the study design, data collection and analysis, decision to publish, or preparation of the manuscript. (P) The author(s) received no specific funding for this work.
Source: Stuart Peirson – PLOS Image Source: This NeuroscienceNews.com image is adapted from the PLOS press release. Original Research: Full open access research for “Melanopsin Regulates Both Sleep-Promoting and Arousal-Promoting Responses to Light” by Violetta Pilorz, Shu K. E. Tam, Steven Hughes, Carina A. Pothecary, Aarti Jagannath, Mark W. Hankins, David M. Bannerman, Stafford L. Lightman, Vladyslav V. Vyazovskiy, Patrick M. Nolan, Russell G. Foster, and Stuart N. Peirson in PLOS Biology. Published online June 8 2016 doi:10.1371/journal.pbio.1002482
Cite This NeuroscienceNews.com Article
[cbtabs][cbtab title=”MLA”]PLOS. “Light Color Determines Sleepiness Versus Arousal in Mice.” NeuroscienceNews. NeuroscienceNews, 15 August 2016. <https://neurosciencenews.com/arousal-light-color-mice-4849/>.[/cbtab][cbtab title=”APA”]PLOS. (2016, August 15). Light Color Determines Sleepiness Versus Arousal in Mice. NeuroscienceNews. Retrieved August 15, 2016 from https://neurosciencenews.com/arousal-light-color-mice-4849/[/cbtab][cbtab title=”Chicago”]PLOS. “Light Color Determines Sleepiness Versus Arousal in Mice.” https://neurosciencenews.com/arousal-light-color-mice-4849/ (accessed August 15, 2016).[/cbtab][/cbtabs]
Melanopsin Regulates Both Sleep-Promoting and Arousal-Promoting Responses to Light
Light plays a critical role in the regulation of numerous aspects of physiology and behaviour, including the entrainment of circadian rhythms and the regulation of sleep. These responses involve melanopsin (OPN4)-expressing photosensitive retinal ganglion cells (pRGCs) in addition to rods and cones. Nocturnal light exposure in rodents has been shown to result in rapid sleep induction, in which melanopsin plays a key role. However, studies have also shown that light exposure can result in elevated corticosterone, a response that is not compatible with sleep. To investigate these contradictory findings and to dissect the relative contribution of pRGCs and rods/cones, we assessed the effects of light of different wavelengths on behaviourally defined sleep. Here, we show that blue light (470 nm) causes behavioural arousal, elevating corticosterone and delaying sleep onset. By contrast, green light (530 nm) produces rapid sleep induction. Compared to wildtype mice, these responses are altered in melanopsin-deficient mice (Opn4-/-), resulting in enhanced sleep in response to blue light but delayed sleep induction in response to green or white light. We go on to show that blue light evokes higher Fos induction in the SCN compared to the sleep-promoting ventrolateral preoptic area (VLPO), whereas green light produced greater responses in the VLPO. Collectively, our data demonstrates that nocturnal light exposure can have either an arousal- or sleep-promoting effect, and that these responses are melanopsin-mediated via different neural pathways with different spectral sensitivities. These findings raise important questions relating to how artificial light may alter behaviour in both the work and domestic setting.
“Melanopsin Regulates Both Sleep-Promoting and Arousal-Promoting Responses to Light” by Violetta Pilorz, Shu K. E. Tam, Steven Hughes, Carina A. Pothecary, Aarti Jagannath, Mark W. Hankins, David M. Bannerman, Stafford L. Lightman, Vladyslav V. Vyazovskiy, Patrick M. Nolan, Russell G. Foster, and Stuart N. Peirson in PLOS Biology. Published online June 8 2016 doi:10.1371/journal.pbio.1002482