Scientists have discovered the brain's "on" switch, enabling them to turn the consciousness of monkeys on and off at will.

A team co-led by Yuri Saalmann, an assistant professor at the University of Wisconsin, Madison, discovered that stimulating a tiny chamber deep in the brain called the central lateral thalamus would instantly wake up a monkey that had been knocked out with a powerful anaesthetic.

Tiny electric shocks "switched on" the brains of the macaque, awakening them in seconds.

Saalmann said: "We found that when we stimulated this tiny little brain area, we could wake the animals up and reinstate all the neural activity that you'd normally see in the cortex during wakefulness."

"They acted just as they would if they were awake. When we switched off the stimulation, the animals went straight back to being unconscious."