(HealthDay News) -- Each day a clock in the brain that governs daily activities -- sleeping, waking, body temperature, eating, arousal -- is guided by light detected by the eyes.
This is called our internal clock. Scientists have discovered that a gene for a light-sensitive protein in the eye -- separate from vision -- is what resets the clock, according to the U.S. National Institutes of Health.
In studies, mice lacking this gene were not able to regulate their internal clocks, which scientists call circadian rhythms.
These mice appeared healthy but ran on wheels for hours in constant darkness, when a mouse with the "normal" gene would have gone to sleep.