Ten percent of the brain myth
The 10 percent of the brain myth is the widely perpetuated urban myth that most or all humans only make use of 10 percent (or some other small percentage) of their brains. It has been misattributed to many people, including Albert Einstein. By extrapolation, it is suggested that a person may harness this unused potential and increase intelligence.
Changes in grey and white matter following new experiences and learning have been shown, but it has not yet been proven what the changes are. The popular notion that large parts of the brain remain unused, and could subsequently be "activated", rests in popular folklore and not science. Though mysteries regarding brain function remain—e.g. memory, consciousness—the physiology of brain mapping suggests that all areas of the brain have a function. While all areas of the brain have a function, not all are connecting at the same moment. Recent research has shown psilocybin to connect many more areas of the brain that are normally not connected or don't connect at the same time.
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; thereafter, 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 percent of his latent mental ability". This book was not the first to use the 10 percent figure, which was already circulating within the self-help movement before then; for example, the book Mind Myths: Exploring Popular Assumptions About the Mind and Brain includes a chapter on the ten percent myth which shows a self-help advertisement from the 1929 World Almanac containing the line "There is NO LIMIT to what the human brain can accomplish. Scientists and psychologists tell us we use only about TEN PERCENT of our brain power."
In the 1970s, psychologist and educator Georgi Lozanov proposed the teaching method of suggestopedia believing "that we might be using only five to ten percent of our mental capacity". The origin of the myth has also been attributed to Wilder Penfield, the U.S.-born neurosurgeon who was the first director of Montreal Neurological Institute of McGill University.
According to a related origin story, the ten percent 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 ten percent myth. The myth might have been propagated simply by a truncation of the idea that some use a small percentage of their brains at any given time. In the same article in Scientific American, John Henley, a neurologist at the Mayo Clinic in Rochester, Minnesota states: "Evidence would show over a day you use 100 percent of the brain".
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 may be that a large number of questions about the brain have not been fully answered.
Neurologist Barry Gordon describes the myth as 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 percent 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 one is doing, all brain areas are always active. Some areas are more active at any one time than others, but barring brain damage, there is no part of the brain that is absolutely not functioning.
- The brain is enormously costly to the rest of the body, in terms of oxygen and nutrient consumption. It can require up to 20 percent of the body's energy—more than any other organ—despite making up only 2 percent of the human body by weight. If 90 percent 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; given the historical risk of death in childbirth associated with the large brain size (and therefore skull size) of humans, there would be a strong selection pressure against such a large brain size if only 10 percent was actually in use.
- Brain imaging (neuroimaging): 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 percent of cells were unused, then this technique would have revealed that.
- Synaptic pruning: Brain cells that are not used have a tendency to degenerate. Hence if 90 percent of the brain were inactive, autopsy of normal adult brains would reveal large-scale degeneration.
In popular culture
Several books, films, and short stories have been written closely related to this myth. They include the novel The Dark Fields, its film adaptation Limitless (claiming 20 percent rather than the typical 10 percent), and the 2014 film Lucy, all of which operate under the notion that the rest of the brain could be accessed through use of a drug. Lucy, in particular, depicts a character who gains increasingly godlike abilities once she surpasses 10 percent - though the film suggests 10 percent represents brain capacity at a particular time rather than permanent usage.
Some New Age proponents propagate the "ten percent of brain" 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.
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