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.
"Imagine if we could access 100 per cent. Interesting things begin to happen." But real-life neuroscientists are unimpressed.
Barbara Sahakian, professor of clinical neuropsychology at the University of Cambridge in Britain, said the idea that we only use a small percentage of our brain doesn't make any sense.
The entire brain is active and in use all the time - the neurons, the nerve cells involved in thought - are always doing something.
Different regions of the brain are used for different bodily functions, such as seeing, hearing, speaking and controlling muscles.
The idea that 90 per cent of the brain is just unused does not stand up to analysis, Professor Sahakian said.
She thinks the 10 per cent figure was simply plucked out of the air by early psychologists before it was made famous in Dale Carnegie's 1936 book, How to Win Friends and Influence People.
Sam Wang, a neuroscientist at Princeton University in the US, thinks the myth has been perpetuated by the self-help industry.
People like to believe they can "expand the mind", he suggests.
It is also a concept believed by 65 per cent of Americans, according to a survey last year by the Michael J. Fox Foundation for Parkinson's Research - 5 per cent more than believe in evolution.
- Daily Mail