Does the average person only use 10% of their brain capacity?

Lucy 2014 film posterThe new action-thriller Lucy features Scarlett Johansson whose character is kidnapped and forced to work as a drug mule for a gang operating in dystopic Taiwan. After being surgically implanted with a mysterious drug, the substance inadvertently leaks into her body before it can be removed. The drug transforms Lucy giving her new powers including telekinesis, eliminating all sensations of pain, and the ability to absorb knowledge instantaneously.

The release poster for ‘Lucy’ claims that “the average person uses 10% of their brain capacity”, which is a widely perpetuated urban legend. It is believed the myth emerged in the 1890’s, when William James, known as the father of American psychology, wrote in The Energies of Men: “We are making use of only a small part of our possible mental and physical resources.”

The 10% figure is associated with lack of knowledge about certain sections of the brain. Scientists for a long time did not know the purpose of the frontal lobe of the brain or areas of the parietal lobe, and damage to these areas did not result in motor or sensory deficits. They were deemed ‘silent areas’ of the brain and for some time their purpose remained illusive. Now we know that they are linked to functions such as  planning, motivation, attention, and language processing.

Barry Gordon, a neurologist at Johns Hopkins School of Medicine in Baltimore told Scientific American that although it is an alluring notion, the 10 percent myth “is so wrong it is almost laughable.” Gordon says that the durability of the myth stems from people’s conceptions about their own brains: they see their own inability to perform a task or activity as evidence of untapped potential in the brain. However, at certain points in a person’s life, we may be using only 10 percent of our brains (e.g. when resting).

Dismissing the myth he told the magazine: “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…Let’s put it this way: the brain represents three percent of the body’s weight and uses 20 percent of the body’s energy.” Even a simple action like clenching and unclenching your hand, or saying a few words, requires activity in far more than a tenth of the brain.

At any given moment, not all of the brain’s regions are active concurrently. Neural imaging technology has shown that, like the body’s muscles, most are continually active over a 24-hour period. John Henley, a neurologist at the Mayo Clinic in Minnesota states that: “Evidence would show over a day you use 100 percent of the brain.” Even in sleep, areas such as the prefrontal cortex, which controls things like higher level thinking and self-awareness, or the somatosensory areas, which help people sense their surroundings, are active, Henley explained.

If the 10% figure refers to using 10% of brain cells, this still does not stand up to scrutiny. When any nerve cells are no longer of use they either degenerate and die or they are colonised by other areas nearby. Keeping brain tissue alive consumes up to 20% of total body energy in adults (up to 60% in children) and utilises 20% of the oxygen we breathe, according to cognitive neuroscientist Sergio Della Sala. The fact that the brain is such a huge drain on our resources makes the 10% notion appear even more absurd.

Director Luc Besson seems to have taken the 10% figure at face value and he capitalises on the myth to full effect, giving the protagonist Lucy the potential to move objects with her mind and physically overcome her enemies with ease. Morgan Freeman, who plays Dr Norman in the film, repeated the myth in a recent interview with ABC News and so it appears that some of the pople working on ‘Lucy‘ seem to have been convinced by it. The film has a fairly simple narrative and contains several scenes of gratuitous violence, so shouldn’t take much mental resource to follow if you only use 10% of your brain.

‘Lucy’ opens in the US on 25 July, Australia on 31 July and the UK on 22 August

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