No doubt you have heard the saying that we humans only use 10 percent of our brain. It is a phrase that has been used in everything from adverts for computer hard drives to choosing which airline to fly, and is so common that a large proportion—around 25-30 percent—of well-educated university students believe that it is true, as reported in a paper back in 1998 by Higbee and Clay. Even our kids believe it. Earlier this year, I gave a lecture on the brain to 300 teenage school children. We wanted to get an idea of what they knew already before the lecture so we asked questions such as do you know what a brain cell is called and so on. We also asked them how much of their brain did they think humans use. Nearly all of them gave the 10 percent figure.

As familiar as the 10 percent claim may seem, it is a myth. Moreover, it’s a pernicious myth exploited by those who want to sell us hope of greater success by tapping into hidden reserves of mental energy either through brain enhancing programmes or supernatural powers. There is something appealing about the idea that each us harbours untapped powers. The shelves of pop psychology are dominated by books that claim they will help you unleash your full potential and this strategy of selling false neuroscience is shamelessly perpetuated by authors and
publishers who think that the public prefer to buy books that they believe will empower them by unlocking the unused secret 90 percent of their brain.

The truth is you use all of your brain. Humankind did not come all this way down the difficult evolutionary path that ruthlessly whittled away our descendents with less complex brains just so we modern humans could loaf around using only one tenth of that hard won mental machinery. Neurons are continually discharging nerve impulses at a background rate. If they are not active they lose their connectivity. When they are stimulated, this idling rate rapidly increases like the chatter of a Geiger counter but they are always on as it were.

No one is quite sure who started this rumor but some think that it can be traced to the North American father of psychology, William James who wrote in The Energies of Men, “We are making use of only a small part of our possible mental and physical resources.” Taken out of context, this could mean that we don’t actually use part of our brain, which is an unfortunate claim coming from someone who otherwise, anticipated many of the major discoveries in the study of the brain and mind.

James was making an impassioned plea to readers in an essay about striving but unfortunately when it comes to your brain, not using any part of it does not make any scientific sense. You can of course, learn to use strategies to improve performance and that is perfectly valid but that does not mean that you are not using some parts of your brain. All of the brain is always on and is always hungry. The brain weighs on average only 2 percent of the body but uses 20 percent of the energy. A recent imaging paper by Zhu and colleagues shows that the grey matter, which is predominantly composed of neurons, uses up 77 percent of the energy requirements of the brain. It may sound like vast amounts of energy are being expended but if you remember that overall hourly body energy usage is about 100W. So the brain uses the equivalent of a 20W domestic light. Maybe that's where bright ideas come from? Hold on, a light bulb just went on over my head. I feel another urban myth in the making.

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