A new study appearing in the journal PLOS Biology is the first to demonstrate that the color of light influences the circadian clock in any mammalian species.
According to scientists at the University of Manchester, UK, the color of light has a major impact on how mammalian body clock measures the time of day. Image credit: Axel Kristinsson / CC BY 2.0.
“This is the first time that we’ve been able to test the theory that color affects the body clock in mammals,” said Dr Timothy Brown of the University of Manchester, UK, who is the senior author on the study.
“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.”
“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 travelers wanting to minimize jet lag.”
In their study, Dr Brown and his colleagues at the University of Manchester looked at the change in light around dawn and dusk to analyze 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.
“Using environmental measurements, we show here that mammalian blue-yellow color discrimination provides a more reliable method of tracking twilight progression than simply measuring irradiance,” the scientists wrote in the PLOS Biology paper.
“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.”
The researchers 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.
They used measurements of the changes in the color spectra 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.
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Walmsley L et al. 2015. Colour As a Signal for Entraining the Mammalian Circadian Clock. PLoS Biol 13 (4): e1002127; doi: 10.1371/journal.pbio.1002127
