Scientists at Oxford University have been trying to work out how the brain suddenly switches off in sleep. The ‘Sandman’ switch is triggered by falling levels of the chemical dopamine which is known to keep people awake. Researchers found that sleep-control neurons are either on or off based on the activity of the ‘Sandman’ switch, a physical gate which allows or blocks electrical signals to the cells. When dopamine production stops, the switch is flicked and sleep is triggered. Read on.