We Use Way More Than 10 Percent of Our Brains

“It is estimated most human beings only use 10 percent of their brain’s capacity,” lectures Professor Norman, played by actor Morgan Freeman, in the trailer for the new movie Lucy. “Imagine if we could access 100 percent. Interesting things begin to happen.”

I know I haven’t earned my Ph.D. yet, professor, but I beg to differ. You see, we all access 100 percent of our brains—every day. And we don’t have to be telekinetic or memorize an entire deck of cards to do it.

In the film, which opens next Friday in the U.S. and August 22 in the U.K., Lucy (Scarlett Johansson) is forced to work as a drug smuggler for a Taiwanese mob. But the drug they’ve implanted into her body leaks into her system, enabling her somehow to “access 100 percent” of her brain. Eventually, among other things, Lucy finds she can move objects with her mind, choose not to feel pain, and memorize copious amounts of information.

In a way, the myth that we only use 10 percent of our brains is rather inspiring. It may motivate us to try harder to tap into some mysterious, intact reservoir of creativity and potential. There are even products that promise on the market promising to unlock that other 90 percent.

As ludicrous as the claim is, however, two-thirds of the public and half of science teachers still believe the myth to be true. When University College London neuroscientist Sophie Scott attended a first aid course, her instructor assured the class that head injuries weren’t dangerous because “90 percent of the brain [doesn’t] do anything.”

How did this misconception come about?

We may be able to track its earliest roots to psychologist William James, who wrote in his 1907 text The Energies of Men that “we are making use of only a small part of our possible mental and physical resources.” I tend to agree with this sentiment when I spend my evenings on the couch watching reality television, but, of course, James didn’t really intend to lend credence to this 10 percent myth.

But someone else did. Lowell Thomas, in his foreword to Dale Carnegie's 1936 book How to Win Friends and Influence People, reinterpreted the statement and, it seems, sprinkled in a few of his own ideas. "Professor William James of Harvard," Thomas wrote, "used to say that the average person develops only 10 percent of his latent mental ability."

Here’s the thing: The brain has rapidly tripled its original size across two million years of human evolution. Despite only accounting for 2 percent of our body weight, the brain gobbles up a whopping 20 percent of our daily energy intake. Our brains are also remarkably efficient, having evolved gyri which have dramatically increased our cortical surface-area-to-total volume ratio relative to other species. If we only used 10 percent of our brains, that would mean that we’re all effectively evolving in the opposite direction—and very quickly.

Another obvious way we know that we use more than 10 percent of our brain is through functional magnetic resonance imaging and positron emission tomography. fMRI and PET are imaging techniques that reveal areas of relatively high brain activity in real time. Imaging studies tell us that not only are many brain areas recruited when performing even the simplest of tasks, like watching a movie, but that the activity between these areas is extremely dynamic.

Plus, the “use it or lose it” adage seems to hold particularly true in brain health. A 2012 study by Schafer and colleagues at Harvard found that neural immune cells called microglia can remove idle, but otherwise healthy, synapses (connections) between brain cells. If we were only regularly using 10 percent of our brains at any given time, we might all be prone to cerebral atrophy, resembling patients with neurodegenerative diseases like Alzheimer’s.

The 10 percent myth may have been further perpetuated by something that is true: Despite the brain having nearly 100 billion neurons, this cell type is vastly outnumbered by another: glial, or "glue," cells. These cells are responsible for maintaining homeostasis, providing structural support, insulating neurons with myelin, and removing pathogens and debris. The actual ratio of glial cells to neurons is disputed, although many texts claim it may be roughly 10:1. In other words, neurons are only 10 percent of our entire brain.

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Think about yourself right now: Are you engaging your muscles to sit yourself upright? Using your hand to scroll your computer mouse (or your thumb on your mobile device)? Perhaps you’re eating something, too, or listening to music? And are you breathing? Then rest assured, you’re using more than 10 percent of your brain right now.

Morgan Freeman, you may have once played God in a movie, but clearly you need a primer on how that older character's most incredible creation—the brain—functions! (Love you, Morgan!)

Originally published at The Conversation UK.