Origins of the 10 Per cent Myth
The notion that humans only operate at a tenth of their theoretical capacity has been floating around since the late Victorian Era, when modern medicine was still tottering about with pseudo-sciences like phrenology (skull science) or osteopathic manipulative medicine (holistics). And like most urban legends, the root of the 10 per cent myth has no less than a half dozen potential sources.
The earliest potential source comes from the work of Jean Pierre Flourens, one of the founding fathers of modern cognitive sciences, inventor of anaesthesia, and the man credited with proving that consciousness resides in the brain not the heart. His pioneering work in demonstrating the regional functionality of the brain's hemispheres often characterised a large portion of the cerebral hemispheres as the "silent cortex," which may have influenced subsequent researchers into believing that this region, now known as the association cortex, has no function.
Another source of the myth could be the Energy Reserve Theory quackery, put forth by Harvard psychologists William James and Boris Sidis in the 1890s. Their research, which consisted of raising Sidis' prodigy son William (the kid had a reported IQ of 250-300, roughly double Einstein of 160) in an accelerated developmental environment. The researchers took the child's massive intellect as proof that every human must contain some hidden reserve of mental and phsyical energy. In his treatsie, The Energies of Men, James states, "We are making use of only a small part of our possible mental and physical resources." This notion was later popularised by Lowell Thomas in a foreword to Dale Carnegie's How to Win Friends and Influence People:"Professor William James of Harvard used to say that the average man develops only ten per cent of his latent mental ability."
The 10 per cent myth received another credibility boost in the 1920s and '30s through the work of American Psychologist Karl Lashley. Through his attempts to quantify the relationship between brain mass and function, Lashley discovered that rats could relearn specific tasks after enduring damage to their cerebral cortex. However, our understanding of brain function at that time was still disgustingly crude, and the connections he suggested between mass action (that learning is governed by the cerebral cortex as a whole, not specific regions atop it) and equipotentiality (that sensory perception can be relearned by other regions of the brain after damage) have given rise to the myth.
How We Know We Use More Than 10 Per cent of Our Brains?
Thankfully, the field of neuroscience has advanced by leaps and bounds since the first half of last century and we have come to learn that, like sperm, every brain cell is sacred.
The human brain constitutes 1/40th of a human's overall mass, on average, but consumes a full fifth of our calories. From an evolutionary standpoint, wherein every other organ in our bodies has been bred and naturally selected over eons for efficiency, having a brain that sucks down 20 per cent of our daily energy reserves for 10 per cent efficiency simply makes no sense.
Clinical research over the past 80 years has born out similar evidence. Even a small degree of damage to any region of your grey matter—either from stroke, injury, or disease—can result in catastrophic neurological declines. "Numerous types of brain imaging studies show that no area of the brain is completely silent or inactive," Dr. Rachel C. Vreeman and Dr. Aaron E. Carroll wrote in a study of medical myths. "Detailed probing of the brain has failed to identify the 'non-functioning' 90 per cent."
Conversely, electrical stimulation therapies have yet to uncover any hidden reserves of intellect, though the practice is showing promise for treating epilepsy and a small number of other neurological conditions. A 2008 study published in Scientific American by Barry Gordon, a neurologist of the John Hopkins School of Medicine, states unequivocally that "we use virtually every part of the brain, and that [most of] the brain is active almost all the time." In fact, research with MRI and other imaging technologies have shown that almost all of the brain is active almost all of the time—even during menial or routine tasks.
"Let's put it this way," he told Scientific American. "The brain represents three per cent of the body's weight and uses 20 per cent of the body's energy."
So What Would Happen If We Actually Did Only Use 10 Per cent of Our Brains?
Let's say for a second that removing 90 per cent of your brain somehow wouldn't kill you outright, what would happen? According to the University of Washington, the results aren't pretty:
If the average human brain weighs 1,400 grams (about 3 lb) and 90% of it was removed, that would leave 140 grams (about 0.3 lb) of brain tissue. That's about the size of a sheep's brain. It is well known that damage to a relatively small area of the brain, such as that caused by a stroke, may cause devastating disabilities. Certain neurological disorders, such as Parkinson's Disease, also affect only specific areas of the brain. The damage caused by these conditions is far less than damage to 90% of the brain.
That's right, take away 90 per cent of your brain and you're officially reclassified as a sheep.
So when you see Scarlett Johansson gaining powers of telekinesis and beyond as she unlocks more and more of her brain's potential, know that all she's really tapping into are one screenwriter's flight of fancy. [Britannica - Wiki 1, 2 - Scientific American - About - John Hopkins University - News.Au - University of Washington]