Though factors of intelligence can increase with training, the popular notion that large parts of the brain remain unused, and could subsequently be "activated", rests more in popular folklore than scientific theory. Though mysteries regarding brain function remain—e.g. memory, consciousness — the physiology of brain mapping suggests that most if not all areas of the brain have a function.
Origin
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 effect 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. 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. Indeed, it is easy to imagine that the myth propagated simply by a truncation of the statement that "humans use 10% of their brains at any given time."
Although 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.
The origin has also been attributed to Dr. Wilder Penfield, the U.S.-born neurosurgeon who was the first director of Montreal Neurological Institute of McGill University
Refutation
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.
- Brain scans have shown that no matter what we're doing, our brains are always active. Some areas are more active at any one time than others, but unless we have brain damage, there is no one part of the brain that is absolutely not functioning.
- 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. 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".
Perpetuation in pop culture
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 as well as "Lest We Remember" (which actually features total recall, a different concept based on similar premises) and "Foundation and Empire "by Isaac Asimov. These, however, do not imply that the human brain is, or should be inherently capable of, this exponential growth, while in the "Foundation" it is claimed by the person using it, but he was established earlier to have no formal education.
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 genetics professor who also affirms the unused-brain myth to hint at the human potential for superpowers. In the novel The Dead Zone, the protagonist's ability to see the future is attributed to the reactivation of a dormant part of his brain (Albeit caused to compensate for brain damage suffered while he was in a coma).
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 no scientifically verified body of evidence supporting the existence of such powers.
The core premise of the 1991 romantic comedy Defending Your Life is that people on Earth only use 3-5% of their brain and spend their time on Earth conquering fear. Once Earthlings, referred to as "Little Brains" conquer fear and learn to use more of their cognitive power, they graduate to a higher plane. Otherwise their soul is reincarnated and they are sent back to Earth to try again.
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