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What Percentage Of The Human Brain Do We Use?

It may be an enticing prospect that we have bags of untapped brain power, using just 10 percent of our brains – but that doesn’t mean there’s any truth to it.

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Maddy Chapman

Maddy is a Editor and Writer at IFLScience, with a degree in biochemistry from the University of York.

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Is it 10 percent as Hollywood would have you think?

Image credit: BlueBackIMAGE/Shutterstock.com

If you cast your mind back to 2014, you may remember a certain film that got us all talking about brain capacity. Lucy was based on the premise that we only use 10 percent of our brains, and while we know that to be a myth, it still begs the question: What percentage of the brain do we actually use?

Come with us as we attempt to debunk one of Hollywood’s favorite bits of cerebral pseudoscience.

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What percentage of the human brain do we use?

The brain is made up of three main regions: the cerebrum, the cerebellum, and the brain stem. Different areas of the brain function both independently and together to coordinate tasks – so depending on what we’re doing, the amount of the brain being utilized will vary. While it may be true that not every region is always firing at any given moment, this doesn’t mean that some parts go unused.

"We use virtually every part of the brain," neurologist Barry Gordon at Johns Hopkins School of Medicine in Baltimore told Scientific American in 2008. "[Most of] the brain is active almost all the time," 

In fact, in a 24-hour period, all regions of our most complex organ will get used. Even when we’re resting or sleeping, much of the brain is active. 

"Evidence would show over a day you use 100 percent of the brain," added John Henley, a neurologist at the Mayo Clinic in Rochester, Minnesota. 

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That doesn’t necessarily mean that removing part of the brain or sustaining brain damage leaves people unable to perform day-to-day tasks, Henley continued, “The brain has a way of compensating and making sure that what's left takes over the activity.” 

It’s this plasticity that explains how some people missing parts of their brain are, remarkably, still able to function (take the case of the bilingual woman missing a part of the brain responsible for language processing, for example).

How do we know 10 percent is a fallacy?

A technique called functional magnetic resonance imagining (fMRI) has been used to disprove the 10 percent myth. It measures blood flow and oxygenation in the brain to detect activity in different regions. This technique has found that, even when performing simple tasks, much more than just a tenth of the brain is active.

“But maybe the 10 percent refers to number of brain cells,” wrote Claudia Hammond in 2012 for BBC Future. “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.”

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Then there’s the fact that the 10 percent figure is simply nonsensical, neuroscientist Amy Reichelt argued in a 2014 piece for The Conversation. Our brains make up just 2 percent of our body mass and yet use 20 percent of our energy – why would we waste such a large amount of our bodily resources to power only a tiny percentage of it?

So there you have it, the 10 percent misconception is consigned to sci-fi. While we’re on the topic of brain-based myths, we’re happy to tell you that the brain doesn’t stop developing at 25, either.

All “explainer” articles are confirmed by fact checkers to be correct at time of publishing. Text, images, and links may be edited, removed, or added to at a later date to keep information current. 


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