It is a concept that has been repeated so often that it has almost become accepted wisdom.
But the old saying that human beings use only 10 per cent of their brains is a myth, scientists say.
The fallacy forms the central concept in Scarlett Johansson's forthcoming blockbuster, in which she plays a character who "learns" to use her entire brain.
Lucy, a sci-fi film to be released next month, features Johansson using her newly discovered brainpower to develop lightning quick reflexes and even to control time.
In the film, directed by Luc Besson, Morgan Freeman plays a neuroscientist who says: "It is estimated most human beings only use 10 per cent of the brain's capacity.