Why Do We Only Use 10 Percent of the Brain?

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When someone says you are only using 10 percent of your brain, what does that mean? And how do we know that we only use 10 percent? We would have to know what 100-percent capacity looks like before we could say we presently use one-tenth of it, right? Here is the science behind it all.

Have you ever met anyone who is missing 90 percent of their brain? Probably not. You have never heard of anyone with that much brain missing, because pretty much all areas of the brain are capable of electrical and chemical activity. People wouldn’t be able to function with that tidbit of grey matter. Even the regions of the cortex in blind people that normally process vision are co-opted for other functions. Everyone makes use of the entire brain.

Neuromythology in Popular Culture

“The average person uses 10 percent of their brain capacity. Imagine what she could do with 100 percent.” So reads a poster for Lucy, the 2014 action-thriller starring Scarlett Johansson. This sounds intriguing—but it also sounds very familiar. That is because Hollywood loves to revive the 10-percent myth every few years (e.g., Phenomenon, 1996; Limitless, 2011).

Studies from neuroscience show that the brain uses about 20 percent of the body’s energy, and it would not make much sense to dedicate so many resources to such a small percentage of the brain. Along those lines, biologists say that we would not have evolved such big brains (about 1,400 cubic centimeters) if we only used just a little bit of them.

Where Did This Originate?

Who was the first to float this 10-percent idea, anyway? One possibility is William James, one of the great experimental psychologists from the early 20th century. He basically argued that we only operate on a fraction of our full mental potential, and that we can raise our IQ by tapping into this unused portion.

Another possibility comes from the world of marketing. Apparently, the 10-percent idea goes back at least as far as a 1929 self-help ad that states, “There is no limit to what the human brain can accomplish. Scientists and psychologists tell us we use only about ten percent of our brain power.”

My favorite origin theory points to Wilder Graves Penfield, a Montreal neurosurgeon once named the “greatest living Canadian,” and who spent a great deal of time in the 1940s and 50s poking around the brains of fully awake, conscious people. There are no pain receptors in the brain, so once you apply local anesthetic and cut into the skull, you can prod all you want with an electric probe. Penfield documented—correctly, I might add—that only 10 percent of his probes resulted in observable events. A blink, a twitch, humming, left big toe wiggling, etc. Somehow this got twisted and shortened to “90 percent of the brain is not being used.” The truth, of course, is that 90 percent of the time, the brain is just doing something that is not a detectable event, like retrieving a memory or pondering the future.

It should surprise no one that Hollywood keeps revisiting the 10-percent concept. Would it not be super cool to somehow unlock reserves of psychic power to win over friends and dominate enemies? Certainly. But in real life, at least for now, we’ll just have to figure out a way to do that with the brains we’ve got.

Next up, we will talk about the neuromythology behind right brain versus left brain exaggerations.