The internal clock in the brain helps animals keep track of time and alter their behavior depending on whether day or night is approaching. Now, a new study shows that this internal clock syncs with external time using not just changes in the intensity but also the color of ambient light.
In the journal PLOS Biology, researchers from the University of Manchester in the UK write how assessing external time is thought to rely on the ability to sense large changes in light intensity that occur as dawn and dusk approach.
But the color of light also changes during these twilight transitions, so the team wanted to investigate if this also features in the function of the body clock.
This is the first time scientists have been able to test the idea that colors of light affect the body clock in mammals, as Dr. Timothy Brown, of Manchester’s Faculty of Life Sciences, explains:
“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.”
For the study, the researchers set up their instruments at the top of one of the university buildings and made detailed recordings of the daily color changes that occur in the sky over the course of a month.
The data confirmed that light changes not only in intensity but also in color. As the sun rises and sets, the twilight is bluer than during the full light of day.
The researchers then used the recordings to create an artificial sky in the lab so they could see what happened as mice were exposed to it.
As expected for nocturnal animals, after a few days of living under the artificial sky, the mice’s highest body temperatures occurred just after dusk, when the sky became a darker blue, indicating that their body clock was working correctly.
But when the scientists changed the artificial sky so only the intensity of the light and not its color changed, the mice became more active before dusk, showing their body clock was not properly aligned to day-night.
In earlier tests, the team had recorded electrical activity in the mice’s brain clocks as they were exposed to different colors of light. They found that many of the brain cells in this part of the brain were more sensitive to blue-yellow color changes than to changes in light intensity.
“In sum, our data reveal a new sensory mechanism for estimating time of day that should be available to all mammals capable of chromatic vision, including humans.”
Dr. Brown says he and his colleagues are excited about their findings because they believe they also apply 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 December 2014, Medical News Today learned of a study led by the St. Louis University in Missouri that revealed a potential way to control the body’s internal clock. By targeting a protein called REV-ERB with a drug called SR9011, the researchers found they could increase wakefulness and reduce REM (rapid eye movement) and slow-wave sleep in mice with dysfunctional circadian rhythms that possessed anxious behavior.