No, it’s not true. But don’t feel bad about believing it:
In one study, when asked “About what percentage of their potential brain power do you think most people use?,” a third of psychology majors answered 10% (Higbee & Clay, 1998, p. 471). Fifty-nine percent of a sample of college-educated people in Brazil similarly believe that people use only 10% of their brains (Herculano-Houzel, 2002). Remarkably, that same survey revealed that even 6% of neuroscientists agreed with this claim!
Despite how common the belief is, it’s false:
Neurologist Barry Gordon describes the myth as laughably false, adding, “we use virtually every part of the brain, and that [most of] the brain is active almost all the time”. Neuroscientist Barry Beyerstein sets out seven kinds of evidence refuting the ten percent myth:
- Studies of brain damage: If 90% of the brain is normally unused, then damage to these areas should not impair performance. Instead, there is almost no area of the brain that can be damaged without loss of abilities. Even slight damage to small areas of the brain can have profound effects.
- Evolution: The brain is enormously costly to the rest of the body, in terms of oxygen and nutrient consumption. It can require up to 20% of the body’s energy—more than any other organ—despite making up only 2% of the human body by weight. If 90% of it were unnecessary, there would be a large survival advantage to humans with smaller, more efficient brains. If this were true, the process of natural selection would have eliminated the inefficient brains. By the same token, it is also highly unlikely that a brain with so much redundant matter would have evolved in the first place.
- Brain imaging: Technologies such as Positron Emission Tomography (PET) and functional magnetic resonance imaging (fMRI) allow the activity of the living brain to be monitored. They reveal that even during sleep, all parts of the brain show some level of activity. Only in the case of serious damage does a brain have “silent” areas.
- Localization of function: Rather than acting as a single mass, the brain has distinct regions for different kinds of information processing. Decades of research have gone into mapping functions onto areas of the brain, and no function-less areas have been found.
- Microstructural analysis: In the single-unit recording technique, researchers insert a tiny electrode into the brain to monitor the activity of a single cell. If 90% of cells were unused, then this technique would have revealed that.
- Neural disease: Brain cells that are not used have a tendency to degenerate. Hence if 90% of the brain were inactive, autopsy of adult brains would reveal large-scale degeneration.
In the October 27, 2010 episode of MythBusters, the hosts used magnetoencephalography and functional magnetic resonance imaging to scan the brain of someone attempting a complicated mental task. Finding that well over 10% was active at once, they declared the myth “busted”.
So how did the belief come about?
So, if the 10% myth is so poorly supported, how did it get started? Attempts to track down this myth’s origins haven’t uncovered any smoking guns, but a few tantalizing clues have materialized (Beyerstein, 1999c; Chudler, 2006; Geake, 2008). One stream leads back to pioneering American psychologist William James in the late 19th and early 20th centuries. In one of his writings for the general public, James said he doubted that average persons achieve more than about 10% of their intellectual potential. James always talked in terms of underdeveloped potential, never relating it to a specific amount of the brain engaged. A slew of “positive thinking” gurus who followed weren’t as careful, though, and “10% of our capacity” gradually morphed into “10% of our brain” (Beyerstein, 1999c). Undoubtedly, the biggest boost for the self-help entrepreneurs came when journalist Lowell Thomas attributed the 10% brain claim to William James.