Do You Use 10% of Your Brain? Why Do We Think That?

(Last Updated On: April 7, 2021)

At some point it took off that we only use like 10% of our brains. Which seems like a ridiculous notion when you think about it too hard–but it also seems reasonable if you think about it too hard in the other direction. That is to say the brain is really weird and we don’t know all that much about it. Though it’s generally agreed upon that you use all of your brain. There’s no latent 90% that you can unlock to turn yourself into a superhuman or something. But where did the myth come from?

Also the brain is the only organ that named itself. 

Further Reading: What Is a Split Brain?

How Do We Know We Use All of Our Brains?

For starters it’s kind of a logic thing. If we only used 10% of our brains way back in caveman times, someone would have come along who used 100% and they would have been way better at being alive than everyone else. Which means they would have had a lot of kids, some of whom likely also used 100% of their brains, making them more successful to have more 100%-brain-using offspring. Point is, natural selection generally picks the most efficient systems, or at least Pareto efficient ones. Having 90% of the grey matter rattling around in your skull being useless is ridiculously inefficient.

But also we’ve studied it, because we study everything. While humans don’t physically have the largest brains, we are up there when it comes to how big our brains are compared to the rest of our bodies. Plus we have a notoriously overdeveloped cerebral cortex which is over 80% of our brain’s 100 billion neuron mass. All of this sounds great, but it turns out our brains might not be as special as we think–around 100 billion neurons is expected for a primate brain as big as ours, and the cerebral cortex is not as overdeveloped as we think it is–it’s pretty in line with primates too. The human brain, though, is remarkably efficient. We can use the resources available to us really well–but we don’t have any more than we would otherwise expect.

Scanning around the brain also tells us that we do use our brain in full. Just not all of it at once. Depending on what you’re doing, different parts of your brain will fire–but over the course of any given day every part of your brain will have gotten a workout. 


Impressively though, our brains can reorganize and make do with substantially less. It’s called neuroplasticity, and part of it is simply how learning works. We generate less neurons as we age, and our brains physically peak well before our intelligence as people does. Sidebar, your brain does keep making neurons in old age, contrary to the belief that you’re stuck with what you have once you’re no longer a teenager. It just slows down. 

Anyway, our brains reorganize themselves to preserve and strengthen connections we use often–that’s why it’s easier to pick up skills when you’re younger. Your brain’s more flexible. But it’s also why you can still be really good at something later in life–your brain has specialized.

Even more impressive is how the brain can adapt to damage. No seriously, some people can live with half their brain removed. It’s our brain’s ability to compensate for areas that are failing by having other parts pick up the slack that makes it so hard to study the brain. Hard to figure out what controls what when resources can be redirected.

Why Do We Think We Only Use 10%?

We can actually kind of pinpoint this. For starters, only using 10% of your brain is a really good excuse when you feel dumb. Because of course you did something stupid, you’re not even using your entire brain!

A 1907 edition of the Science journal had an article published by William James. He argued that we don’t use all of our brains–but he didn’t say how much we did or didn’t use. 

Here’s the wack stuff though. Remember that 100 billion neuron figure for the brain? That’s actually a figure most textbooks just cite without a source. Approximations have been made as early as 1988, but no direct estimates for how many neurons our brains have would emerge until 2009. 

We do know that we have about 10 times more glial cells than we do neurons. Which, at first blush tells us neurons make up only about 10% of the brain’s cells, and thus, we only use 10% of the brain

Speaking of brains, use all of it to figure out this word ladder.

About the Author:

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Kyler is a content writer at Sporcle living in Seattle, and is currently studying at the University of Washington School of Law. He's been writing for Sporcle since 2019; sometimes the blog is an excellent platform to answer random personal questions he has about the world. Most of his free time is spent drinking black coffee like water.