According to Seed magazine:
In the 1980s . . .Benjamin Libet performed an experiment that seemed to show that areas of the brain responsible for certain body movements activate before we are conscious of our decision to move. Researchers in Europe recently decided to test Libet's conclusion again. A group of 14 volunteers was asked to press either of two buttons, one with the left hand and one with the right, whenever they wanted, so long as they noted the time when they made their decision. Watching the patterns of activity in the volunteers' brains, researchers could predict which button the individuals would pick up to 10 seconds before they had consciously made their choice.