All of it, just not all at once
Reading this sentence uses the parts of your brain that handle seeing, language and memory. Standing up and walking to the kitchen uses others. No single task needs every region at once, and that’s fine: a piano has 88 keys, and nobody plays them all in the same chord.
Over a whole day, though, the picture is different. Brain imaging shows that most regions are active over a 24-hour period, and John Henley, a neurologist at the Mayo Clinic, put it plainly to Scientific American: “Evidence would show over a day you use 100 percent of the brain.” Even asleep, as Eric Chudler’s Neuroscience for Kids site notes, the brain is still busy, just in a different state.
Two giveaways
Small damage, big effects. If 90% of the brain were spare, most injuries would change nothing. In fact, as Chudler writes, “destruction of even small areas of the human brain can have devastating effects on behavior.” That’s why surgeons map the brain carefully before an operation: there is no safe, unused 90% to cut through.
An expensive organ. Your brain is only a few percent of your body weight, yet it uses up to about 20 percent of your body’s energy. Bodies don’t usually spend that much on tissue that sits around doing nothing.
Where “10%” came from
Nobody measured it. The best-documented trail runs through the psychologist William James, who wrote in The Energies of Men that “we are making use of only a small part of our possible mental and physical resources” (quoted by Chudler). That is a claim about untapped potential, like an unpractised piano player, and it has no number in it.
The number turned up later. In his 1936 foreword to Dale Carnegie’s How to Win Friends and Influence People, the broadcaster Lowell Thomas wrote that James used to say the average person develops only 10 percent of their latent mental ability (Wikipedia and Chudler both trace it there). From “potential we don’t develop” to “brain we don’t use” is a small step in a retelling, and a huge one in meaning. Along the way the line was also pinned on Albert Einstein, with no evidence that he said it.
You’re in good company
This is one of the stickiest brain myths around. In a survey published in 2012, 48% of the UK teachers and 46% of the Dutch teachers who took part thought it was true, and these were teachers interested enough in the brain to answer a survey about it. Another 26% of the UK teachers said they didn’t know.
It survives because it’s such a hopeful idea: a hidden 90% waiting to be switched on. The true version is hopeful too. You can’t unlock spare brain, but you can get better at almost anything by practising it, which is a much better deal.
Want the longer version, with brain scans, films like Lucy and what really helps you think better? Read the 10% myth, explained.
