Research by scientists at The University of Manchester has revealed that the color of light has a major impact on how our body clock measures the time of day.
It’s the first time the impact of color has been tested and demonstrates that color provides a more reliable way of telling the time than measuring brightness.
In research being published on April 17th in the Open Access journal PLOS Biology, the researchers looked at the change in light around dawn and dusk to analyse whether color could be used to determine time of day. Besides the well-known changes in light intensity that occur as the sun rises and sets they found that during twilight, light is reliably bluer than during the day.
The scientists next recorded electrical activity from the body clock while mice were shown different visual stimuli. They found that many of the cells there were more sensitive to changes in color between blue and yellow than to changes in brightness.
The scientists then used measurements of the changes in the color spectra taken from the top of the University’s Pariser Building, to construct an artificial sky which recreated the daily changes in color and brightness.
Mice were placed beneath the sky for several days and their body temperature was recorded. As expected for nocturnal creatures, the highest body temperatures occurred just after night fell when the sky turned a darker blue – indicating that their body clock was working optimally.
When just the brightness of the sky was changed, with no change in the color, the mice became more active before dusk, demonstrating that their body clock wasn’t properly aligned to the day night cycle.
Dr Timothy Brown from the Faculty of Life Sciences led the research: “This is the first time that we’ve been able to test the theory that color affects the body clock in mammals. It has always been very hard to separate the change in color to the change in brightness but using new experimental tools and a psychophysics approach we were successful.”
He continues: “What’s exciting about our research is that the same findings can be applied to humans. So in theory color could be used to manipulate our clock, which could be useful for shift workers or travellers wanting to minimise jet lag.”
About this neurobiology research
Research: This study was funded by the Biotechnology and Biological Sciences Research Council.
Source: Morwenna Grills – University of Manchester Image Credit: The image is credited to David Gennard, The University of Manchester Original Research: Full open access research for “Colour As a Signal for Entraining the Mammalian Circadian Clock” by Lauren Walmsley, Lydia Hanna, Josh Mouland, Franck Martial, Alexander West, Andrew R. Smedley, David A. Bechtold, Ann R. Webb, Robert J. Lucas, and Timothy M. Brown in PLOS Biology. Published online April 17 2015 doi:10.1371/journal.pbio.1002127
Colour As a Signal for Entraining the Mammalian Circadian Clock
Twilight is characterised by changes in both quantity (“irradiance”) and quality (“colour”) of light. Animals use the variation in irradiance to adjust their internal circadian clocks, aligning their behaviour and physiology with the solar cycle. However, it is currently unknown whether changes in colour also contribute to this entrainment process. Using environmental measurements, we show here that mammalian blue–yellow colour discrimination provides a more reliable method of tracking twilight progression than simply measuring irradiance. We next use electrophysiological recordings to demonstrate that neurons in the mouse suprachiasmatic circadian clock display the cone-dependent spectral opponency required to make use of this information. Thus, our data show that some clock neurons are highly sensitive to changes in spectral composition occurring over twilight and that this input dictates their response to changes in irradiance. Finally, using mice housed under photoperiods with simulated dawn/dusk transitions, we confirm that spectral changes occurring during twilight are required for appropriate circadian alignment under natural conditions. Together, these data reveal a new sensory mechanism for telling time of day that would be available to any mammalian species capable of chromatic vision.
“Colour As a Signal for Entraining the Mammalian Circadian Clock” by Lauren Walmsley, Lydia Hanna, Josh Mouland, Franck Martial, Alexander West, Andrew R. Smedley, David A. Bechtold, Ann R. Webb, Robert J. Lucas, and Timothy M. Brown in PLOS Biology. Published online April 17 2015 doi:10.1371/journal.pbio.1002127
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