Hello everyone,

Lots of sci-fi novels and films capture the idea that we have an untapped potential hidden away in our heads – the unused 90% of our brains. The idea that we only use 10% of our brains is widespread and has been around for some time. Is this really true? We asked 14 experts in neuroscience, ‘Do we only use 10% of our brain at any one time?’, here is what they said…

EXPERT CONSENSUS

Do we only use 10% of our brain at any one time?

‘No’ based on 14 expert responses

What is the ‘10% of the brain’ theory and where did it come from?

This is the theory that we only use 10% of our brains, and if we were somehow able to ‘unlock’ the other 90%, we could become more intelligent or successful. Some sci-fi films even imagine that using more of our brain would endow us with superhuman abilities!

The exact origin of this theory is not clear, but it may have come from some real scientific experiments that looked at brain function after damage. Dr Jonathon Morrow, an expert in neuroscience and psychiatry from Michigan University in the USA, says that the ‘10% of the brain’ theory “probably originated as a misinterpretation of lesion studies by the famous neurosurgeon Wilder Penfield. He showed that most of the brain could be lesioned without any obvious loss of function, and that only about 10% was in this sense absolutely necessary. However, the fact that the brain can recover from such injuries is due primarily to redundancy and an ability for different brain areas to compensate for each other when necessary. It does not mean that those areas are inactive in a normal, healthy brain.”

What is the evidence that we only use 10% of our brains?

The overwhelming majority of responses were ‘No, we don’t only use 10% of our brain at one time’. Dr Mark Meadowcroft, an expert in neuroscience from Pennsylvania State University in the USA, says “The notion that we only utilize 10% of our brain is a myth and is completely untrue. The entire brain volume, whether it be human or otherwise, is completely utilized.”

There is no evidence that we only use 10% of our brain, and there is lots of evidence to suggest that we use all of our brain for most activities. Dr Morrow says “Modern imaging studies have clearly demonstrated that pretty much all of the brain is in continuous use.” These imaging studies use machines like functional magnetic resonance imagine (fMRI) scanners to look for brain activity. Such studies have found that even when you do nothing, most regions of your brain are active.

What do we mean by brain activity?

‘Brain activity’ can be measured it lots of different ways. fMRI scanning looks at blood flow to different parts of the brain. Another type of measurement, called electroencephalography (EEG) measures the electrical activity which occurs when neurons communicate with each other (or when neurons ‘fire’). In order for us to walk, talk and do all the activities we are able to do, our neurons need to fire in a very specific, coordinated way.

Even if 100% of our brains are active as measured by fMRI scanning, not all of our neurons are firing all the time. Dr Eric Blalock, a neuroscience expert from Kentucky University in the USA, says “In the sense that only 10% of the neurons in the brain may be firing at a given moment, sure. People that have 100% of their neurons firing at once? We have a name for that, it's not called 'transcendental telepathy', it's called 'global epilepsy' and it will kill you.”

Clearly, increasing the percentage of neurons in our brain that fire at the same time will not necessarily increase intelligence. Dr Blalock explains “Think about it this way- your heart is a pump- in order for it to work, some parts of it MUST be relaxed while other parts contract, that's how blood moves from the atria to the ventricles- if ALL the muscles in the heart constricted at once, you would not have discovered a way to increase cardiac output to make a super athlete, instead you would have a heart attack.”

“So the neurons of the brain should be active at different times, in a coordinated way, like the muscle fibers of the heart. On another level, the cells of the brain are busy all the time. Neurons fire action potentials. To do that, they have to expend energy to create a membrane potential. It costs energy to maintain that membrane potential. So a neuron 'at rest' is like an archer with an arrow knocked and the bow drawn, pointing at a target. There is tension there and energy is expended to maintain that 'ready' position. When the neuron fires, it is like loosing the arrow. And then the neuron must recover and get ready to do it all over again. Whether it is resting, firing or recovering, the neuron is busy doing stuff.”

The takeaway:

We do not only use 10% of our brain.

May the facts be with you!

Eva

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