Are you really only using 10 percent of your brain?

How do you cook up an idea that's so plausible and appealing, yet completely mistaken? You start by misinterpreting the incomplete scientific knowledge of the time. Then, take a couple of esteemed men of science and misquote them.

In the 19th and early 20th centuries, medical researchers who studied the brains of animals and stroke victims discovered that different brain areas controlled different activities. In the 1870s, for example, German physiologists Gustav Fritsch and Eduard Hitzig electrically stimulated a spot in a dog's brain and noticed that the dog moved its right front paw. When they surgically removed that tissue from two other dogs, they noticed that the dogs not only couldn't use the paw, but seemed unaware of it [source: Finger]. Over the next half-century, other researchers eagerly zapped various parts of animal and human brains in an attempt to map brain function. But they were only able to figure out what about 10 percent of the brain did, because when they stimulated the other 90 percent, no muscles twitched. Scientists labeled that area the silent cortex because its function was unknown. We now know that's the area that, among other things, controls language and abstract thinking [source: Wanjek]. Non-scientists, however, mistakenly took this to mean that most of the human brain was on permanent vacation.

Through the miracle of misquotation, some celebrated minds also have helped promote the 10 percent brain myth. Pioneering psychologist-philosopher William James, wrote in a 1906 essay that he believed "we are only making use of a small part of our possible mental and physical resources" [source: James]. Journalist Lowell Thomas -- the same promotional genius who helped make Lawrence of Arabia into a legend -- tinkered with James' words to help market self-improvement guru Dale Carnegie's 1936 book "How to Win Friends and Influence People." In the book's forward, Thomas wrote that "the average person develops only 10 percent of his latent mental ability," and attributed that information to James [source: Carnegie].

Since then, other self-help authors have attributed the idea that we only use 10 percent of the brain's capacity to Albert Einstein -- a curious source, since his expertise was in physics, not neuroscience. In 2004, a thorough search by staffers of the Einstein archives at California Institute of Technology, however, found no evidence that he ever made such a statement [source: Beyerstein].

This may come as a surprise -- accustomed as you probably are to the idea that nine-tenths of your brain's 100 billion or so neurons are wasting away in Margaritaville. But today's brain researchers, who have much more sophisticated tools than the old electrode-zappers, have discovered that the human brain doesn't seem to have any dormant regions. "It turns out, though, that we use virtually every part of the brain, and that [most of] the brain is active almost all the time," Johns Hopkins University neurologist Barry Gordon explained to Scientific American in 2008 [source: Boyd].

如果你停下来思考一下,这令人震惊的狂欢ation is only logical. As science journalist Christopher Wanjek points out in his 2005 book "Bad Medicine," if a human needed only 10 percent of the brain to function, it's unlikely that evolution would have allowed the other 90 percent to develop. The brain, after all, is a glutton for resources. Though it amounts to only five percent of the body's weight, it consumes 20 percent of our supply of oxygen and glucose, and demands a continual supply of both to keep working [source: Wanjek]. Additionally, if a human being only needed 10 percent of his or her brain to function normally, we'd be invulnerable to brain diseases (not to mention head traumas short of decapitation). Instead, as brain researcher Barry J. Beyerstein noted in a 2004 Scientific American article, destroying far less than 90 percent of the brain can have a catastrophic effect, and there doesn't seem to be any portion of the brain that a person can lose without experiencing some sort of loss of function [source: Beyerstein]. Wanjek explains: "A person would be comatose if 90 percent of the brain -- any 90 percent -- were inactive" [source: Wanjek].

It is true that different parts of the brain do different things, and not all at the same time. But while not every single ounce of that three-pound hunk of goo inside your skull is necessarily working at any given moment, brain scans show that over a 24-hour period, pretty much the whole brain gets a workout, and most of the parts are continually active. Even when you're sleeping, regions such as the frontal cortex, which controls higher-level thinking and self-awareness, and the somatosensory areas, which help you to sense your surroundings, remain active [source: Boyd].

Unlike their 19th century predecessors, who had to be content with mucking around with scalpels and shooting electricity into random spots of the brain to see what happened, today's neuroscientists have at their disposal an array of sophisticated technology for probing the mysteries of how the brain works.

One extremely useful tool for researchers who treat brain diseases and injuries is functional magnetic resonance imaging (fMRI), which uses a powerful magnetic field, radio frequency pulses and a computer to produce a series of detailed pictures of a person's brain as it works. An fMRI not only provides a look at brain's anatomy, but also to determine precisely which parts are handling activities such as thinking, speech, movement and sensation. (That sort of study is called brain mapping) [source:RadiologyInfo.org].

Another way to look at the brain is to use a computerized axial tomography (CT) scan, which takes a series of X-rays of the brain and uses a computer to combine them into an image [source: National Headache Foundation]. Yet another imaging technology is the positron emission tomography (PET) scan. For this scan, a small amount of radioactive material is injected into a vein, inhaled or swallowed. The radioactive material accumulates in the brain and gives off gamma rays, which are captured with a special type of camera [source:Radiologyinfo.org]. PET scans are useful for identifying brain abnormalities and studying which parts of the brain are most active during certain tasks [source:Mayo Clinic].

复杂的脑成像工具也使神经细胞osurgeons to plan operations and to cut with more precision when they remove tumors, so that there is less damage to patients' brains. When a talented young French horn player was recently diagnosed with a large brain tumor, for example, doctors feared that it might end his musical career. Dr. Susan Bookheimer, a neurosurgeon at UCLA medical school, had him undergo an fMRI scan while reading sheet music and fingering an instrument, so she could pinpoint the areas of the brain he was using. As a result, surgeons were able to avoid damaging those areas when they removed the tumor, and the musician was back playing in a few months [source:Apple.com].