Studies using fruit flies have been key to finding the molecular gears of biological clocks and the cells that control circadian rhythms. This image shows how time-of-day information flows in the fruit fly brain: Clock neurons (stained in blue, mid-left and right) communicate with other nerve cells (stained in red, inner top right, left, and bottom), which then signal to additional neurons (stained in green, outer top right, left, and bottom). Credit: Matthieu Cavey and Justin Blau, New York University.

How are circadian rhythms related to sleep?

Circadian rhythms help determine our sleep patterns. The body’s master clock, or SCN, controls the production of melatonin, a hormone that makes you sleepy. It receives information about incoming light from the optic nerves, which relay information from the eyes to the brain. When there is less light—like at night—the SCN tells the brain to make more melatonin so you get drowsy. Researchers are studying how shift work as well as exposure to light from mobile devices during the night may alter circadian rhythms and sleep-wake cycles.

How are circadian rhythms related to jet lag?

People get jet lag when travel disrupts their circadian rhythms. When you pass through different time zones, your biological clocks will be different from the local time. For example, if you fly east from California to New York, you “lose” 3 hours. When you wake up at 7:00 a.m. on the east coast, your biological clocks are still running on west coast time, so you feel the way you might feel at 4:00 a.m. Your biological clocks will reset, but this often takes a few days.