The new Luc Besson movie Lucy, starring Scarlett Johansson, opens tomorrow in theaters countrywide. It's based on the immortal myth that we use only 10 percent of our brains. Johansson's character is implanted with drugs that allow her to access 100 percent of her brain capacity. She subsequently gains the ability to learn Chinese in an instant, beat up bad guys, and throw cars with her mind (among other new talents). Morgan Freeman plays neuroscientist Professor Norman, who's built his career around the 10 percent claim. "It is estimated most human beings use only 10 percent of the brain's capacity," he says, "Imagine if we could access 100 percent."

As it happens, I've written a book all about brain myths (Great Myths of the Brain; due out this November). I thought I'd use what I learned to give you a 60-second explainer on the 10 percent myth.

Where does the myth originate?

No-one knows for sure. A popular theory has it that the journalist Lowell Thomas helped spread the myth in his preface to Dale Carnegie's block-buster self-help book How to Win Friends and Influence People. Thomas misquoted the brilliant American psychologist William James as saying that the average person specifically "develops only 10 percent of his latent mental ability." In fact James had referred more vaguely to our "latent mental energy." Others have claimed that Einstein attributed his intellectual giftedness to being able to use more than 10 percent of his brain, but this is itself a myth. Another possible source of the 10 percent myth is neurosurgeon Wilder Penfield's discovery in the 1930s of "silent cortex" - brain areas that appeared to have no function when he stimulated them with electricity. We know today that these areas are functional.

Is Luc____y the first movie to use the 10 percent myth as a premise?

No, the 2011 movie Limitless, starring Bradley Cooper was based on the same idea, except the precise figure was placed at 20 percent. Cooper's character takes a pill that lets him access the full 100 percent. Both the 1991 film Defending Your Life (thanks to A Voice in The Wilderness for flagging this up in the comments) and Flight of the Navigator (1986) include claims that most of us use a fraction of our brains. The myth is also invoked in the TV series Heroes, to explain why some people have special powers.

Does anyone really believe this myth anymore?

Apparently so. For example, in 2012, a survey of school teachers in Britain and The Netherlands found that 48 per cent and 46 per cent, respectively, endorsed the myth. Last year, a US survey by the Michael J Fox Foundation for Parkinson's Research found that 65 percent of people believed in the myth.

Is there any truth to the myth?

Certainly there is no truth to the idea that we only use 10 percent of our neural matter. Modern brain scans show activity coursing through the entire organ, even when we're resting. Minor brain damage can have devastating effects - not what you'd expect if we had 90 percent spare capacity. Also, consider the situation when neural tissue representing a limb is rendered redundant by the loss of that limb. Very quickly, neighbouring areas recruit that tissue into new functions, for example to represent other body regions. This shows how readily the brain utilises all available neural tissue.

So why does the myth persist?

For many people, the 10 percent myth sounds both feasible and appealing because they see it in terms of human potential. Many of us believe that we could achieve so much more - learning languages, musical instruments, sporting skills - if only we applied ourselves. It's easy to see how this morphs into the shorthand idea that we use just 10 percent of our brain's capacity or potential.

Does it matter that films like Lucy spread the 10 percent myth?

It certainly bothers a lot of neuroscientists. There are so many widely held misunderstandings about the brain that scientists find it extremely unhelpful to have more nonsense spread to millions of movie goers. Other people I've spoken to are more optimistic and think that audiences will realize that the claims are not meant to be taken seriously. I have to admit, I enjoyed Limitless despite the daft premise.

I haven't yet seen Lucy. I'd love to hear your thoughts on whether it's a good movie in spite of the bad science, and if so, does that justify further propagation of the 10 percent myth?