When it comes to the human brain, even the simplest of acts can be counter-intuitive and deceptively complicated. For example, try stretching your arm.

Nerves in the limb send messages back to your brain, but the subjective experience you have of stretching isn’t due to these signals. The feeling that you willed your arm into motion, and the realisation that you moved it at all, are both the result of an area at the back of your brain called the posterior parietal cortex. This region helped to produce the intention to move, and predicted what the movement would feel like, all before you twitched a single muscle.

Michel Desmurget and a team of French neuroscientists arrived at this conclusion by stimulating