Randy Nelson, co-author of the study and professor of neuroscience and psychology at The Ohio State University in Columbus, examined the role of specialized photosensitive cells in the retina -- called ipRGCs -- that don't have a major role in vision, but detect light and send messages to a part of the brain that helps regulate the body's circadian clock. This is the body's master clock that helps determine when people feel sleepy and awake.
Other research suggested these light-sensitive cells also send messages to parts of the brain that play a role in mood and emotion.
"Light at night may result in parts of the brain regulating mood receiving signals during times of the day when they shouldn't," said study co-author Tracy Bedrosian, a former graduate student at Ohio State, who is now a postdoctoral researcher at the Salk Institute. "This may be why light at night seems to be linked to depression in some people."
The study, published in The Journal of Neuroscience, found hamsters exposed to red light at night had significantly less evidence of depressive-like symptoms and changes in the brain linked to depression, compared with those that experienced blue or white light, but the hamsters that fared the best were those that had total darkness at night.
"If you need a night light in the bathroom or bedroom, it may be better to have one that gives off red light rather than white light," Bedrosian said.
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