The Best Circadian Light

            On January 28^th, 2020, Dr. Daniel Cavanaugh presented a talk on the circadian rhythms of feeding behavior in Drosophila melanogaster at Loyola University Chicago. He defined circadian rhythms to be an internal driver of external behaviors which allows for organisms to appropriately respond to their environment. This phenomenon is no different in humans – we are also driven by an internal clock that determines when we should engage in certain behaviors, such as sleeping and eating. This internal clock, whether fruit fly or human, is deeply impacted by stimuli from our environment, such as the day-night cycle. Interestingly enough, like our circadian rhythm, our mood, alertness, and memory and cognitive function are also impacted by this day-night cycle. The amount and type of light we get daily impacts the circadian rhythms of our general cognitive health. For example, seasonal affective disorder (SAD), a common mood disorder characterized by depression-like symptoms that arise around the fall or winter seasons, is thought to be caused by less exposure of direct sunlight during the duration of such seasons. The widespread experience of this mood disorder provides anecdotal evidence that light does impact our mood and circadian rhythm, yet studies done on how light affects our brain have been miniscule until recently.

An article from ScienceDaily, “Let there be ‘circadian’ light,” published on February 20^th, 2020, discusses the science behind the impact light has on our moods and the subsequent application of that science to create a light that could make us happier and more productive indoors. The article was of particular interest because we live in a world where most of our time is unfortunately spent indoors, where the usage of artificial light could be impacting our circadian rhythm, mood, alertness, and other cognitive functions. The article discusses a recently published scientific study titled “A color vision circuit for non-image-forming vision in the primate retina,” where researchers from the University of Washington Health Sciences identified specific cone receptors in the retina that, interestingly, signaled to regions of the brain that regulate circadian rhythms and mood levels. These receptors not only responded strongly to blue light but also to long wavelength light, like orange light and red light; in other words, they strongly respond to the natural lights of sunrise and sunset. As a result of their ability to encode spectral light, these photoreceptors were found to be crucial in accurately setting our internal clock to match with our environment’s daily cycle. Since they respond so strongly to these wavelengths, it was concluded that the wavelengths of sunrise and heavily impact the brain regions that regulate both our circadian rhythms and mood. Thus, researchers are now saying that any lighting that is able to stimulate as many of these crucial photoreceptors as possible will be beneficial for our cognitive health, as it will mimic the natural conditions under which our brain evolved.

The discovery of this new cone photoreceptor in the retina has excited researchers for the future of circadian rhythm research and the subsequent applications for such research. Current lights on the market that have tried to create the best beneficial light for treating mood disorders like SAD unfortunately have not been as effective due to the lack of scientific data. Current lights are built to be brighter than normal lights in an attempt to stimulate the pigment melanopsin, which was thought to have played an important role in signaling to circadian rhythms brain regions. However, the cone photoreceptors in the scientific study were found to be a thousand times more sensitive to light than this pigment, suggesting that they play a more significant role in this signaling and that future light products should focus on stimulating these specific receptors.

These new findings will no doubt give some more insight into the creation of an artificial light that closer mimics natural sunlight. Because our circadian rhythms have evolved to respond to natural light, it is essential for us to shape our modern environment after the conditions we evolved under for the sake of our health. With the emergence of these circadian rhythm studies, we are making progress in bettering our cognitive health indoors.

References

Patterson, S. S., J. A. Kuchenbecker, J. R. Anderson, M. Neitz, and J. Neitz. 2020. A Color Vision Circuit for Non-Image-Forming Vision in the Primate Retina. Current Biology. doi: 10.1016/j.cub.2020.01.040

University of Washington Health Sciences/UW Medicine. "Let there be 'circadian' light: New study describes science behind best lights to affect sleep, mood and learning." ScienceDaily. ScienceDaily, 20 February 2020. www.sciencedaily.com/releases/2020/02/200220141731.htm