The colors of a sunset could be more than just a nice picture. It might be a subtle signal to our bodies that we should reset our internal clock, the biological rhythm that guides everything from sleep to digestion patterns.
According to a new study on mice, the small rodents use light’s changing color to set their own internal clocks, a finding that scientists believe is valid for humans, as well.
Researchers have known about the part light plays in regulating circadian rhythms, which governs life’s cycle with the 24-hour day. But they did not know how all properties of light, such as brightness and color, contributed to setting that clock.
“As a sort of common sense notion people have assumed that the clock somehow measures the amount of light in the outside world,” explainedTim Brown, a neuroscientist at the University of Manchester in the United Kingdom and an author of the new study. He added: “Our idea was that it might be doing something more sophisticated than that.”
To find out, Brown and his colleagues targeted an area in the brain called the suprachiasmatic nucleus, or SCN, a region common to all vertebrates. It’s where the body keeps time using chemical and electrical rhythms that last, on average, 24 hours. The team wanted to know if color signals sent from the eyes reached the SCN and whether that information affected the timing of the clock.
The team analyzed the electrical chatter of SCN neurons as they exposed mice to different colors and intensity of light. At least 25 percent of the neurons they supervised responded to changes in color, the effect being greater to the shorter wavelength of blue light which colors the skies after dusk.
This means that the signal was being received, but it did not show a measurable effect on the rodent’s internal clocks. So the scientists built an “artificial sky”, which is a group of differently colored LEDs that was placed above a screen. It simulated day and night for caged mice with and without color changes. Mice are nocturnal creatures, with a body temperature is at its highest at night. When natural color was missing from the artificial sky, their internal clocks were disturbed, and the peak temperature happened 30 minutes earlier than under natural conditions.
One of the cool things about the clock, is that when you take it out of an animal and put it in a dish, the cells continue to fire,” Brown mentioned in his comments.
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