We've all heard it said: the old canard that humans "only use ten percent of their brains." Sometimes it's posited along with self help strategies which promise to teach us how to use the elusive other 90%; sometimes it's cited as some kind of proof of psychic powers. In general, it is an alluring thought — that each person among us has a vast, untapped potential that is just begging to be used. Well, bullshit artists of the world: find another bullshit explanation. This one is not true, it has never been true, and the only people who are still perpetuating the myth are the misinformed — who have simply been indoctrinated by the prevalence of these claims — and the dishonest — who most often use this "scientific fact" as supporting evidence for their bullshit claims.

The bottom line: we all use pretty much our entire brains. Even the morons — they just aren't very good at it.

One thing we've noticed is that most people who make this claim really have no idea what they think the claim is even supposed to mean. Sure, we use 10% of our brains, but how is that percentage measured? Does it mean by volume — with the implication that 90% could be chopped out with no ill effects? Or is it by geography, meaning that we could map the unused portions alongside the parts designated (in men) for sports, sex, and beer? Maybe it's by neurons, meaning that 90% of our neural pathways never fire, or perhaps it has something to do with the "conscious" versus "subconscious" mind and the differentiation is harder to illustrate. Or maybe it's some even more nebulous distinction. Just ask the next person who mentions this myth to you to explain what it means, and you'll understand what we're saying — they will likely have no idea.

One of the most common uses of this "theory" crops up whenever someone wants to make an outrageous claim regarding paranormal superhuman abilities, from telepathy and channeling to clairvoyance and precognition. The self-proclaimed psychic natters on and on: "We only use 10% of our brains!" The implication is, of course, that the other 90% — which they are claiming that most humans don't use — is the origin of these amazing powers and unexplained phenomena.

Such fake psychics (a redundant term) are notorious for using unsupported but scientific sounding factoids, incorporating pseudo-scientific jargon and cleverly flowery words, in order to "prove" that their powers and preferred extraordinary phenomena are genuine. Their speech is littered with talk of vibrations and frequencies, energy fields, radiation, resonance and modalities; and they are constantly referring to the fallacious statement that humans use only 10% of their brains. This myth is also perpetuated by the more "mundane" self-help gurus and the such-complete-bullshit-they-should-be-brought-up-on-charges Scientologists.

Most of these people are selling something, and this myth is their "scientific evidence" that their brand of lunacy, their product or service, is genuine. Of course, even if we really did only use 10% of our brains, the fact that we didn't use the other 90% would in no way prove that any of these mystical powers originate there. That is simply an argument from ignorance — we don't know what the missing 90% does, so therefore it must be where the fairies live! This is utter nonsense.

But where did this fairy tale come from? The origin of this preposterous myth is hard to pinpoint exactly, but we'll briefly touch on a few possibilities. Psychologist/philospher William James apparently wrote in The Energies of Men (1908) that "we are making use of only a small part of our possible mental and physical resources." James seems to have given no actual "percentage," nor did he seem to be referring to fractions of actual brain mass when he made this statement.

Perhaps one influence on this erroneous school of thought was the controversy between phrenology — developed by Franz Joseph Gall and Johann Spurzheim — and equipotentiality, supported by researchers such as Marie-Jean-Pierre Flourens and Karl Spencer Lashley. Phrenology — commonly known as the interpretation of the relationship between your personality and the bumps on your head — dictated that different behaviors and characteristics are governed by entirely separate portions of the brain. Equipotentiality supporters believed that although certain portions of the brain had separate functions, they still functioned together as a whole organ. Lashley proved his point by demonstrating that removing different portions of the brains of lab animals had little effect on "specific" behaviors, despite what would be expected of the phrenological model of the brain. The one-to-one relationship between specific neurons and specific mental activity was shown to be fallacious.

Neuroscientists have never proclaimed that humans use such a small percentage of the brain; another misunderstood piece of information may be to blame for this misconception. About a century ago, when this "ten percent" figure was first being bandied about, science was in the beginning stages of mapping the brain and its functions. Scientists noted that they had only mapped the functions of about 10% of the human brain, and in typical propaganda fashion, this was apparently misinterpreted to mean that the remaining 90% had no function at all, when the reality was, these functions merely had yet to be mapped.

Neuroscience has come a long way since the nineteenth (and early twentieth) century. Scientific techniques for mapping the brain originally consisted of autopsies on known victims of brain damage, to match damaged portions of the brain to specific disabilities the victims had developed after the event (such as a stroke) that damaged their brains. Later techniques include animal testing and EEG, and blood flow studies. The development of MRI technology has granted neuroscientists the ability to actually study the activity of the brain as it accomplishes various tasks. In the past 100 years, the functionality of the brain has been quite thoroughly mapped out — there is no mysterious 90% for which scientists can't determine the functions. What's more, analysis of brain activity after damage from injury, stroke, aging (senility or Alzheimer's) or congenital defect has made it quite clear that we use our brains fully.

The parts of the brain certainly are specialized — our various senses and cognitive abilities are each highly concentrated in particular portions. The structure of the brain, however — including a great deal of supportive redundancy — ensures that we are still able to function if some portions of the brain are damaged. And of course, we're always learning more about brain function: recent study has shown that glial cells, a largely overlooked portion of the brain, may play a larger role in cognition than was previously thought.

Do we use 100% of our brains 100% of the time? Well, no. Modern measurements of brain activity have shown that at any given time, only about 5% of the neurons in a human brain are typically active — which is a good thing, since the unchecked torrent of electrical activity resulting from the simultaneous utilization of too many neurons in your brain could cause a seizure. But this is very different from saying that the neurons that are currently inactive are unused — they are used, just not at this instant, and as such, their potential is not "untapped."

Using common sense — and a little education — you can logically deduce that the idea of humans using only 10% of their brains is ridiculous. Your brain makes up about 2% to 5% of your body mass, yet it consumes 20% of the body's resources, such as oxygen and glucose. If such an organ worked at only 10% capacity, that would be a highly inefficient system. It is unlikely that such an organism would be fit enough to survive natural selection and generate offspring that would evolve to be the dominant species on the planet. Additionally, a sheep's brain is approximately 10% the mass of a human brain; if we only used 10% of our brains, we wouldn't be much smarter than a sheep. Hmm — in this case, perhaps those who make this claim really are only using 10% of their brains.

So the next time someone tosses the "we only use ten percent of our brains" tidbit in your lap, here's a handy reply to counter with: "No, you're using the whole package...you're just working with faulty equipment."

Get more information on the "Ten Percent Myth"...

• Straight Dope Article: "Do we really use only 10 percent of our brains?"
• CSICOP Article: "The Ten-Percent Myth"
• Snopes: "The Ten-Percent Myth" by Benjamin Radford
• NESS Article: "Don't You Believe It!"
• "Myths About the Brain: 10 percent and Counting" by Eric H. Chudler, Ph.D.
• National Taiwan Normal University: "The Other Half of the Brain"
• Neuroscience for Kids, by Eric H. Chudler: "Do we use only 10% of our brain?"
• Holysmoke.org: "Scientology and the Great 10% Myth"