No, it’s not true. But don’t feel bad about believing it:
Via 50 Great Myths of Popular Psychology: Shattering Widespread Misconceptions about Human Behavior:
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”.[1] Neuroscientist Barry Beyerstein sets out seven kinds of evidence refuting the ten percent myth:[10]
And:
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?
Via 50 Great Myths of Popular Psychology: Shattering Widespread Misconceptions about Human Behavior:
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.
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