Do we only use 10% of our brains?

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We love the idea that we could be much more intelligent or creative if we harnessed unused parts of our minds. Sadly, Claudia Hammond has some bad news.

It’s amazing just how many medical myths there are to choose from, but one part of the body seems to attract more than its fair share, and that’s the brain. One of my favourite brain myths is the idea that we only use 10% of it. It’s an appealing idea because it suggests the possibility that we could become so much more intelligent, successful or creative, if only you could harness that wasted 90%. This might inspire us to try harder, but unfortunately that doesn’t mean there’s any truth in it.

First of all, it’s important to ask the question – 10% of what? If it is 10% of the regions of the brain to which people are referring, this is the easiest idea to quash. Using a technique called functional magnetic resonance imaging, neuroscientists can place a person inside a scanner and see which parts of the brain are activated when they do or think about something. 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. Even when you think you are doing nothing your brain is doing rather a lot – whether it’s controlling functions like breathing and heart rate, or recalling the items on your to-do list.

But maybe the 10% refers to number of brain cells. Again this doesn’t work. When any nerve cells are going spare they either degenerate and die off or they are colonised by other areas nearby. We simply don’t let our brain cells hang around idly. They’re too valuable for that. In fact our brains are a huge drain on our resources. Keeping brain tissue alive consumes 20% of the oxygen we breathe, according to cognitive neuroscientist Sergio Della Sala.

It is true that nature can sometimes involve some strange designs, but to evolve to have a brain ten times the size we needed would seem very odd, when its large dimensions are so costly to our survival, leading on occasion to obstructed labour and the death of a mother during childbirth if no help is available.

Yet many people do cling on to the idea that we only use 10% of our brains. The idea is so prevalent that when the University College London neuroscientist Sophie Scott was on a first aid course the tutor assured the class that head injuries are not very serious because of the 10% “fact”. He was not only wrong about the 10%, but he was also wrong about the impact of brain damage. Even a small injury can have huge effects on a person’s capabilities. The first aid tutor probably wasn’t bargaining on instructing a professor of neuroscience on the course, but Scott put him right.

Head scratcher

So how can an idea with so little biological or physiological basis have spread so widely? It is hard to track down an original source. The American psychologist and philosopher William James mentioned in The Energies of Men in 1908 that we “are making use of only a small part of our possible mental and physical resources". He was optimistic that people could achieve more, but he does not refer to brain volume or quantity of cells, nor does he give a specific percentage. The 10% figure is mentioned in the preface to the 1936 edition of Dale Carnegie’s best-selling book How to Win Friends and Influence People, and sometimes people say that Albert Einstein was the source. But Professor Della Sala has tried to find the quote, and even those who work at the Albert Einstein archives can find no record of it. So it seems this might be a myth too.

There are two other phenomena that might account for the misunderstanding. Nine-tenths of the cells in the brain are so-called glial cells. These are the support cells, the white matter, which provide physical and nutritional help for the other 10% of cells, the neurons, which make up the grey matter than does the thinking. So perhaps people heard that only 10% of the cells do the hard graft and assumed that we could harness the glial cells too. But these are different kind of cells entirely. There is no way that they could suddenly transform themselves into neurons, giving us extra brain power.

There is a very rare group of patients whose brain scans reveal something extraordinary, though. In 1980, a British paediatrician called John Lorber mentioned in the journal Science that he had patients with hydrocephalus who had hardly any brain tissue, yet could function. This doesn’t of course show us that the rest of us could make extra use of our brains, just that these people have adapted to extraordinary circumstances.

It is, of course, true that if we put our minds to it we can learn new things, and there is increasing evidence in the area of neuroplasticity showing that this changes our brains. But we are not tapping into a new area of the brain. We create new connections between nerve cells or lose old connections that we no longer need.

What I find most intriguing about this myth is how disappointed people are when you tell them it’s not true. Maybe it’s the figure of 10% that is so appealing because it is so low that it offers massive potential for improvement. We’d all like to be better. And we can be better if we try. But, sadly, finding an unused portion of our brains isn’t the way it’s going to happen.

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You can hear more Medical Myths on Health Check on the BBC World Service.

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