It is one of the most widespread beliefs about the brain, and it is false. We do not use "only 10 percent" of our brain: over a day, virtually every region is at work. Here is where the myth comes from, why it is so hard to kill, and what science really shows, including the astonishing case of "the man with a squeezed brain".
Where does the 10 percent myth come from?
Nobody knows exactly who started it. Scientific American, which looked into the question, links it mainly to the American psychologist William James. In the early 20th century, he wrote that we make use of only a small part of our possible mental and physical resources. He was talking about potential, not about a percentage of the brain. Somewhere along the chain of quotes, "a small part" became "10 percent".
The line is also often credited to Albert Einstein, with no source at all. Movies did the rest: films such as Lucy (2014) and Limitless (2011) imagine what would happen if we "unlocked" the other 90%. It is a great plot device, not a scientific fact.
A stubborn myth, even among teachers
In 2012, researchers surveyed 242 teachers in the United Kingdom and the Netherlands about a series of statements on the brain. Asked whether "we only use 10% of our brain", 48% of British teachers and 46% of Dutch teachers answered "true". The study also found that knowing more about the brain in general did not always protect people from such "neuromyths". A simple, flattering idea repeated everywhere ends up sounding obvious.
Part of its success lies in its promise: a vast hidden potential that the right method could "unlock". That promise has been used for decades to sell books, courses and products said to "boost" the brain. The truth is less magical but more encouraging: your whole brain is already at work, and whatever you practise is what gets better.
What brain scans show: the whole brain works
Imaging techniques such as functional MRI and PET scans show which regions use more energy during a task. They reveal no large area that stays switched off. Neurologist Barry Gordon of Johns Hopkins University put it plainly in Scientific American: we use virtually every part of the brain, and most of it is active almost all the time. Mayo Clinic neurologist John Henley added that over a day, you use 100 percent of the brain.
Even at rest, the brain does not switch off. In 2001, neurologist Marcus Raichle and colleagues described a set of regions that stay active when we are doing "nothing", for instance when the mind wanders. It is now called the default mode network.
Far too expensive an organ to be idle
The brain makes up about 2% of body weight, yet it uses around 20% of the body's energy at rest, as Marcus Raichle and Debra Gusnard pointed out. For a living organism, maintaining such a hungry organ with 90% of it doing nothing would make no sense; evolution would not have kept that kind of waste.
It is true that not all neurons fire at once. Each task mostly recruits certain networks, and that is a good thing: activating everything at the same moment would not create a genius but something close to an epileptic seizure. Being used in turns is not the same as being unused.
What about the "man with 10 percent of his brain"?
In 2007, doctors in Marseille, France, described in The Lancet the case of a 44-year-old man who had come in with weakness in one leg. His scans were spectacular. Because of hydrocephalus treated in childhood, the fluid-filled cavities at the centre of his brain had expanded enormously, pushing brain tissue into a thin layer against the skull. Yet he led a normal social and working life, with a measured IQ of 75.
Newspapers called him "the man with 10 percent of his brain". That is misleading. His brain had not disappeared; it was compressed, and his IQ was below average. The case is a striking example of how well the brain can adapt when a problem develops slowly. It does not prove that 90% of our neurons are asleep.
What is true: you can train your abilities
There is no hidden reserve to "unlock". Your brain does change when you learn, though: a skill you practise regularly becomes faster and more reliable. Measuring where you stand on memory, speed or reasoning is a good way to see your strengths.
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Frequently asked questions
Do we really only use 10 percent of our brain?
No. Brain imaging shows that virtually all regions of the brain are active over the course of a day, even at rest.
Where does the 10 percent of the brain myth come from?
It has no single source. It is mostly linked to psychologist William James, who wrote about untapped "resources", and it is wrongly attributed to Einstein. Movies made it popular.
Is the movie Lucy realistic?
No, it is fiction. Firing every neuron at once would not give anyone superpowers; it would look more like an epileptic seizure.
Was there really a man living with 10 percent of his brain?
A man described in Marseille in 2007 lived normally with a brain heavily compressed by fluid. His brain had not disappeared and his IQ was 75: the case shows the brain's ability to adapt, not an unused reserve.
Sources
- Boyd R. (2008). Do People Only Use 10 Percent of Their Brains? Scientific American, 7 février 2008. — scientificamerican.com/article/do-people-only-use-10-percent-of-their-
- Dekker S., Lee N. C., Howard-Jones P., Jolles J. (2012). Neuromyths in Education: Prevalence and Predictors of Misconceptions among Teachers. Frontiers in Psychology, 3, 429. — doi.org/10.3389/fpsyg.2012.00429
- Raichle M. E., Gusnard D. A. (2002). Appraising the brain's energy budget. PNAS, 99(16), 10237–10239. — doi.org/10.1073/pnas.172399499
- Raichle M. E. et al. (2001). A default mode of brain function. PNAS, 98(2), 676–682. — doi.org/10.1073/pnas.98.2.676
- Feuillet L., Dufour H., Pelletier J. (2007). Brain of a white-collar worker. The Lancet, 370(9583), 262. — doi.org/10.1016/S0140-6736(07)61127-1
The MyMindTests team writes about the brain from published studies. Every figure is sourced and checked before publication.