One of the most persistent brain-related myths confronted by frustrated psychology professors is the notion that humans only use 10 percent of the brain. This idea is frequently accompanied by the notion that, if we could only tap into the vast unused portions, we would develop amazing powers of telepathy, clairvoyance, and psychokinesis; be able to levitate, heal disease, and solve humanity’s social problems; achieve perfect recall or instantaneous learning; achieve voluntary control of our bodies’ involuntary functions; achieve world peace; or bend spoons (trivial compared to the others, but quite popular all the same).
This urban legend is now quite widespread, but its origins are shrouded in mystery. What is clear is that it was already widely believed a century ago, and ads for various organizations promising self-improvement were already treating the 10 percent ﬁgure as commonplace knowledge by the 1920s. As often happens with pseudoscience, appeals to authority have helped to spread this notion. In the 1950s, for example, the 10 percent myth appeared in editions of Dale Carnegie’s books, which continue to cast a large shadow over the motivational-seminar industry and thus on corporate America. It is also not unusual to see the myth attributed to William James, the father of American psychology. Another frequently credited source is Albert Einstein—why a physicist should be thought an expert on brain matters is unclear. There is no evidence that either of these two men ever addressed the idea at all, however. The myth is kept alive in an ofﬁcial capacity today by the Transcendental Meditation (TM) organization and Scientology, both of which promise that their adherents will learn to tap this vast unused potential.
One possible source of the myth is a simple misunderstanding of neurological research carried out in the 1930s, when electrical stimulation of the exposed cortex of animal brains became a popular way of discovering the speciﬁc function of various brain areas. When a particular area of a dog’s cortex is stimulated, for example, there is usually a visible motor response. Similar studies of human brains revealed a different pattern, however. Large areas of cortex did not evoke obvious responses, leading researchers to refer to these areas as “silent cortex.” Others may have then taken this to mean that those areas—not 90 percent, but certainly a large proportion of the available tissue—were unused or inactive. No psychologist or neurologist would have interpreted it this way, of course. Far from being silent, those areas not involved in sensation and motor activity are responsible for such things as language, memory, perception, reasoning, and abstract thought.
The myth is easily refuted by modern brain imaging techniques, which show plainly that all the brain is active, all the time. Various tasks that engage particular brain structures may produce a temporary increase in the activity level of those areas, but even in sleep, no area is completely inactive, barring severe tissue damage. Simply put, neurons that show no activity are dead. If 90 percent of the brain were inactive, the tissue would degenerate rapidly. Therefore, techniques that promise to make inactive portions of the brain active are promising, Frankenstein-like, to reanimate dead cells.
Another line of evidence against this myth comes from the study of people who actually do have inactive areas of brain tissue. In stroke victims, the loss of very small areas of tissue, often less than 1 percent of total brain mass, can produce catastrophic loss of function. The almost total loss of memory and sense of self which accompanies advanced cases of Alzheimer’s disease, meanwhile, usually involves damage to 10 to 20 percent or less of the cortex. Damage to relatively small areas of the brain, as one can imagine, can usually be counted on to produce fairly serious damage. In other words, good scientiﬁc reasons exist for this bit of dialogue never being overheard in a hospital emergency room: “Thank God, the bullet passed through the 90 percent of the brain that the victim wasn’t using!”
- Beyerstein, B. L. “Whence Cometh the Myth That We Only Use 10% of Our Brains?” In S. Della Sala, ed. Mind Myths: Exploring Popular Assumptions about the Mind and Brain. New York: Wiley, 1999, pp. 3–24.