I have long believed that if you ever hear anyone say “we only use 10% of our brains,” especially in the process of defending ESP or some similar thing, you can be absolutely certain that you are talking to an ignoramus. Claudia Hammond puts this myth to rest at the BBC:
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…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.
This will not, of course, stop ignorant people from mindlessly repeating that tired old platitude as a fact.