Is It True We Only Use 10% of Our Brains?

George J. Ziogas

The scientific underpinnings of this belief
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The 2014 blockbuster Lucy, starring Scarlett Johansson and Morgan Freeman, explored the fascinating concept of unlocking the vast untapped potential of the human mind. This was not the first time such an idea had been explored in film. It’s a science fiction trope that was also visited in the movie Limitless, starring Bradley Cooper, and the television series that followed. Both movies ask much the same provocative question: What would happen if you were able to unlock 100% of your brainpower? To ask this question, you must presume that humans do not already use their entire brain and all its resources. Is this true?

This inspiring and fascinating premise, is, unfortunately, another example of Hollywood’s tradition of science fiction based on fantasy. The idea that humans only use 10% of their brains has long been debunked by neuroscientists and psychologists, yet it’s still one of the most popular questions posed to them. The answer, according to the book 50 Great Myths of Popular Psychology: Shattering Widespread Misconceptions about Human Behavior is, “Sorry, I’m afraid not.”

Many people continue to believe this myth. It’s disappointing to learn the truth. Wouldn’t it be nice if it were true and some breakthrough, like a pill, could turn a human into a big-brained superhuman with unlimited cognitive powers, including a little telekinesis and maybe a little clairvoyance to boot? There are many charlatans who would like you to believe just that, and that they can tell you how to unlock the 90% of your brain that you, as of now, have no access to. The myth survives even among many psychology students! But it’s an absurd proposition. Let’s look at why.

Brain tissue takes a lot of resources to grow and maintain. In fact, even though it only comprises 2 or 3% of your body weight, it takes up over 20% of the oxygen you breathe. Growing a huge brain, which must be constantly maintained and supplied with energy, only to let 90% of it sit around doing absolutely nothing would be an evolutionary wonder. Natural selection does not favor expensive resources that have no purpose!

Losing even a fraction of 90% of the brain in an accident or another circumstance has devastating consequences. If the part of the brain lost wasn’t being used, losing it wouldn’t matter. Scott O. Lilienfeld and the other authors of 50 Great Myths of Popular Psychology bring up the controversy surrounding Terri Schiavo, the young woman from Florida who was in a persistent vegetative state for 15 years following a cardiac arrest in 1990 that destroyed about 50% of her cerebrum, the upper part of the brain responsible for awareness. Although many people thought they saw hopeful signs of awareness, most experts found no evidence that she retained any capacity for thoughts, perceptions, memories, or emotions. If 90% of the brain is left unused and unnecessary, this should not have happened. In fact, there does not seem to be an area of the brain that can be destroyed without the patient having serious functional deficits.

Electrical stimulation of different parts of the brain during neurosurgery has failed to find any silent areas. Every part of the brain, if stimulated by an electrical current, makes something happen in the patient, such as perceptions, emotions, or movement. Basically, all the parts of the brain, 100% of it, do something!

When an area of the brain goes unused because of injury or disease, it simply degenerates. If there is unused tissue in the brain, it will basically wither away. Either that or the unused tissue will be co-opted by another area of the brain that is in need of new resources. In other words, perfectly good brain tissue would never just sit there taking up space. The tissues would either degenerate or the brain would start using them for some other purpose than they originally were used for.

Given that it seems to be such a silly proposition, how did this myth get started? There’s no evidence of a scientist saying, long ago, “We only use 10% of our brains.” There’s no “smoking gun” as the authors put it, but one possible link is the 19th and 20th-century American psychologist William James, who wrote that he doubted the average human achieves more than 10% of their intellectual potential.

This is obviously a far cry from saying the average human only uses 10% of their brain matter. But enter the “positive thinking” movement and self-help gurus eventually turned “10% of one’s intellectual capacity” into “10% of one’s brain.” At least, this is a likely origin of the myth.

It’s true that in the preface to Dale Carnegie’s How to Win Friends and Influence People, Lowell Thomas attributed the 10% brain statement to William James, and this may well be where the myth really began. For more on this and other huge myths of psychology, see the book.

Lucy may well be an action-packed and entertaining movie. But for science fiction, this and other movies of the type leave a lot to be desired in the science department. Movies are just movies, and you don’t always have to take them too seriously. But the key to good science fiction is that, even when the science is stretched, you’re able to suspend disbelief. When the scientific premise of a movie is based on a complete and utter myth, this can be difficult to do. Regardless, if you watch this movie, whatever you do, don’t watch it to learn about the brain!

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