1.   In complete darkness, the circadian clock still continues to tick vigorously.

2.   But in sighted people the primary mechanism for keeping the circadian clock synchronized with day and night is the input of light through the eyes.

3.   Humans and other mammals have a fosB gene, which has also been linked to phenomena such as resetting the circadian clock and possibly in laying down memory.

4.   It is venerated by the Brits, whose circadian clocks are set by the arrival of the fortnight.

5.   Normally, the study found, bad-mood troughs fall during times when your circadian clock says you should be asleep.

6.   The circadian clock, that self-winding marvel, appears to tick away with swings of a molecular pendulum.

7.   We use it for seeing and for synchronizing our circadian clocks.