HHMI Grants Internal clocks keep pace with the 24-hour cycle of day and night and light and dark, enabling organisms to adapt their behavior accordingly.
Circadian clocks govern many human activities.
From sleep-starved students to active octogenarians, the body intrinsically observes a daily regimen of wakefulness and sleep. Our internal clocks keep us mentally alert during the day and prompt us to rest and recuperate during the night. The pattern continues even in the absence of external cues from the rising and setting sun. Research volunteers living in a bunker in constant dim light naturally maintain a roughly 24-hour cycle of activity and rest. Researchers have concluded that sunrise can reset the clock but that the clock does not depend on sunrise and sunset to keep time.