10% of brain myth
The 10% of brain myth is the widely perpetuated urban legend that most or all humans only make use of 10 percent (or some other small percentage) of their brains. It has been misattributed to people including Albert Einstein. By association, it is suggested that a person may harness this unused potential and increase intelligence.
Though factors of intelligence can increase with training, the idea that large parts of the brain remain unused, and could subsequently be "activated" for conscious use, is without foundation. Although many mysteries regarding brain function remain, every part of the brain has a known function.
One possible origin is the reserve energy theories by Harvard psychologists William James and Boris Sidis in the 1890s who tested the theory in the accelerated raising of child prodigy William Sidis to affect an adulthood IQ of 250–300; thus William James told audiences that people only meet a fraction of their full mental potential, which is a plausible claim. In 1936, American writer Lowell Thomas summarized this idea (in a foreword to Dale Carnegie's How to Win Friends and Influence People) by adding a falsely precise percentage: “Professor William James of Harvard used to say that the average man develops only ten per cent of his latent mental ability."
According to a related origin story, the 10% myth most likely arose from a misunderstanding (or misrepresentation) of neurological research in the late 19th century or early 20th century. For example, the functions of many brain regions (especially in the cerebral cortex) are complex enough that the effects of damage are subtle, leading early neurologists to wonder what these regions did. The brain was also discovered to consist mostly of glial cells, which seemed to have very minor functions. Separately, some early neuroscientists[who?] used the figure of about 10% to refer to the proportion of neurons in the brain that fire at any given time or to refer to percentage of the brain's functions that had been mapped at the time (accounts differ). Dr. James W. Kalat, author of the textbook Biological Psychology, points out that neuroscientists in the 1930s knew about the large number of "local" neurons in the brain. The misunderstanding of the function of local neurons may have led to the 10% myth.
Although all parts of the brain have broadly understood functions, many mysteries remain about how brain cells (i.e., neurons and glia) work together to produce complex behaviors and disorders. Perhaps the broadest, most mysterious question is how diverse regions of the brain collaborate to form conscious experiences. So far, there is no evidence that there is one site for consciousness, which leads experts to believe that it is truly a collective neural effort. Therefore, as with James's idea that humans have untapped cognitive potential, it also is fair to say that a large fraction of questions about the brain have not been fully answered.
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 twenty percent 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.
- Metabolic studies: Another scientific technique involves studying the take-up of radioactively labelled 2-deoxyglucose molecules by the brain. If 90 percent of the brain were inactive, then those inactive cells would show up as blank areas in a radiograph of the brain. Again, there is no such result.
- 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.
Another evolutionary argument would be to consider that given the historical risks of death in childbirth associated with the high brain size and therefore skull size of humans  there would be a strong selection pressure against such a large brain size if, as the myth claimed, only 10% was actually in use. The risk of death is an evolutionary trade off against the gains in functionality of increased brain size.
In the October 27, 2010 episode of MythBusters, the hosts used magnetoencephalography and functional magnetic resonance imaging to scan the brain of someone taking a complicated mental task. Finding that well over 10% was active at once, they declared the myth "busted".
Perpetuation in pop culture
The 10% myth has been spread both unwittingly, by individuals believing it to be fact, and deliberately as a helpful deception. The myth has spread by word of mouth and through various media formats. It is frequently used to give strength to arguments in self-help or some forms of counseling.
Several books, films and short stories have been written closely related to this myth, as well as greatly expanded intelligence, artificially caused and otherwise, in general. The most notable of these is the novel The Dark Fields, and its film adaptation Limitless, which operates under the notion that the rest of the brain could be accessed through use of a drug. The Zombie Survival Guide alleges that humans only use 5% of their brains as a potential explanation of a "sixth sense" in zombies.
Other works involving artificial intellectual enhancement include The Lawnmower Man, the short stories "Understand" by Ted Chiang and "Lest We Remember" (which actually features total recall, a different concept based on similar premises) by Isaac Asimov. These, however, do not imply that the human brain is, or should be inherently capable of, this exponential growth.
The 10% brain myth occurs frequently in advertisements, and is often cited as if it were fact in entertainment media. The pilot episode of Heroes features a professor character who also affirms the unused-brain myth to hint at the human potential for superpowers.
Some New Age proponents propagate this belief by asserting that the "unused" ninety percent of the human brain is capable of exhibiting psychic powers and can be trained to perform psychokinesis and extra-sensory perception. There is currently no scientifically verified body of evidence supporting the existence of such powers.
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- Radford, Benjamin (8 February 2000). "The Ten-Percent Myth". snopes.com. http://www.snopes.com/science/stats/10percnt.htm. Retrieved 2006-04-13.
- Chudler, Eric. "Myths About the Brain: 10 percent and Counting". Archived from the original on 2006-04-02. http://web.archive.org/web/20060402235936/http://brainconnection.com/topics/?main=fa/brain-myth. Retrieved 2006-04-12.
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- Beyerstein, Barry L. (1999). "Whence Cometh the Myth that We Only Use 10% of our Brains?". In Sergio Della Sala. Mind Myths: Exploring Popular Assumptions About the Mind and Brain. Wiley. pp. 3–24. ISBN 0-471-98303-9.
- Swaminathan, Nikhil (29 April 2008). "Why Does the Brain Need So Much Power?". Scientific American. Scientific American, a Division of Nature America, Inc.. http://www.scientificamerican.com/article.cfm?id=why-does-the-brain-need-s. Retrieved 19 November 2010.
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- Bahn, Christopher. "'Limitless' brainpower plot isn't all that crazy". http://today.msnbc.msn.com/id/41953704/ns/today-entertainment/. Retrieved 31 March 2011.
- "Neuroscience For Kids". Eric H. Chudler, Ph.d(University of Washington, Director of Education and Outreach). http://faculty.washington.edu/chudler/tenper.html.
- Ninety Percent Of Your Brain at TV Tropes