http://www.snopes.com/science/stats/10percent.asp
The Ten-Percent Myth
Claim: We use only ten percent of our brains.
Status: False.
One reason this myth has endured is that it has been adopted by psychics and other paranormal pushers to explain psychic powers. On more than one occasion I've heard psychics tell their audiences, "We only use ten percent of our minds. If scientists don't know what we do with the other
ninety percent, it must be used for psychic powers!" In Reason To Believe: A Practical Guide to Psychic Phenomena, author Michael Clark mentions a man named Craig Karges. Karges charges a lot of money for his "Intuitive Edge" program, designed to develop natural psychic abilities. Clark quotes Karges as saying: "We normally use only 10 to 20 percent of our minds. Think how different your life would be if you could utilize that other 80 to 90 percent known as the subconscious mind."
1) Brain imaging research techniques such as PET scans (positron emission tomography) and fMRI (functional magnetic resonance imaging) clearly show that the vast majority of the brain does not lie fallow. Indeed, although certain minor functions may use only a small part of the brain at one time, any sufficiently complex set of activities or thought patterns will indeed use many parts of the brain. Just as people don't use all of their muscle groups at one time, they also don't use all of their brain at once. For any given activity, such as eating, watching television, making love, or reading, you may use a few specific parts of your brain. Over the course of a whole day, however, just about all of the brain is used at one time or another.
2) The myth presupposes an extreme localization of functions in the brain. If the "used" or "necessary" parts of the brain were scattered all around the organ, that would imply that much of the brain is in fact necessary. But the myth implies that the "used" part of the brain is a discrete area, and the "unused" part is like an appendix or tonsil, taking up space but essentially unnecessary. But if all those parts of the brain are unused, removal or damage to the "unused" part of the brain should be minor or unnoticed. Yet people who have suffered head trauma, a stroke, or other brain injury are frequently severely impaired. Have you ever heard a doctor say, ". . . But luckily when that bullet entered his skull, it only damaged the 90 percent of his brain he didn't use"? Of course not.
Variants of the Ten-Percent Myth
The myth is not simply a static, misunderstood factoid. It has several forms, and this adaptability gives it a shelf life longer than lacquered Spam. In the basic form, the myth claims that years ago a scientist discovered that we indeed did use only ten percent of our brains. Another variant is that only ten percent of the brain had been mapped, and this in turn became misunderstood as ten percent used. A third variant was described earlier by Craig Karges. This view is that the brain is somehow divided neatly into two parts: the conscious mind which is used ten to twenty percent of the time (presumably at capacity); and the subconscious mind, where the remaining eighty to ninety percent of the brain is unused. This description betrays a profound misunderstanding of brain function research.
Part of the reason for the long life of the myth is that if one variant can be proven incorrect, the person who held the belief can simply shift the reason for his belief to another basis, while the belief itself stays intact. So, for example, if a person is shown that PET scans depict activity throughout the entire brain, he can still claim that, well, the ninety percent figure really referred to the subconscious mind, and therefore the Ten-Percent figure is still basically correct.
The most powerful lure of the myth is probably the idea that we might develop psychic abilities, or at least gain a leg up on the competition by improving our memory or concentration. All this is available for the asking, the ads say, if we just tapped into our most incredible of organs, the brain. It is past time to put this myth to rest, although if it has survived at least a century so far, it will surely live on into the new millennium. Perhaps the best way to combat this chestnut is to reply to the speaker, when the myth is mentioned, "Oh? What part don't you use?"
