Do We Really Use Only 10 Percent of Our Brain?

It’s one of Hollywood’s favorite bits of pseudoscience: human beings use only 10 percent of their brain, and awakening the remaining 90 percent—supposedly dormant—allows otherwise ordinary human beings to display extraordinary mental abilities. In Phenomenon (1996), John Travolta gains the ability to predict earthquakes and instantly learns foreign languages. Scarlett Johansson becomes a superpowered martial-arts master in Lucy (2014). And in Limitless (2011) Bradley Cooper writes a novel overnight.

This ready-made blueprint for fantasy films is also a favorite among the general public. In a survey, 65 percent of respondents agreed with the statement, “People only use 10 percent of their brain on a daily basis.” But the truth is that we use all of our brain all of the time.

How do we know? For one thing, if we needed only 10 percent of our brain, the majority of brain injuries would have no discernible consequences, since the damage would affect parts of the brain that weren’t doing anything to begin with. We also know that natural selection discourages the development of useless anatomical structures: early humans who devoted scarce physical resources to growing and maintaining huge amounts of excess brain tissue would have been outcompeted by those who spent those precious resources on things more necessary for survival and reproductive success. Tougher immune systems, stronger muscles, better looking hair—just about anything would be more useful than having a head full of inert tissue.

We’ve been able to back up these logical conclusions with hard evidence. Imaging techniques, such as positron emission tomography (PET) and functional magnetic resonance imaging (fMRI), allow doctors and scientists to map brain activity in real time. The data clearly shows that large areas of the brain—far more than 10 percent—are used for all sorts of activity, from seemingly simple tasks like resting or looking at pictures to more complex ones like reading or doing math. Scientists have yet to find an area of the brain that doesn’t do anything.

So how did we come to believe that 90 percent of our brain is useless? The myth is often incorrectly attributed to 19th-century psychologist William James, who proposed that most of our mental potential goes untapped. But he never specified a percentage. Albert Einstein—a magnet for misattribution of quotes—has also been held responsible. In reality, the concept most likely came from the American self-help industry. One of the earliest mentions appears in the preface to Dale Carnegie’s 1936 mega best seller, How to Win Friends and Influence People. The idea that we have harnessed only a fraction of our brain’s full potential has been a staple for motivational gurus, New Age hucksters, and uninspired screenwriters ever since.

Obviously, this is bad news for anyone hoping to find the secret to becoming a genius overnight. The good news, though, is that hard work still works. There is plenty of reason to believe that you can build brainpower by regularly working at challenging mental tasks, such as playing a musical instrument, doing arithmetic, or reading a novel.