Alexander The Great

July 1, 2008

Only Use 10 % of our Brains = Myth

Filed under: Science — alexanderthegreatest @ 10:45 pm
Tags: , , , ,

“Nature encourages no looseness, pardons no errors”
–Ralph Waldo Emerson

This is a popular (nay, undying) urban legend, that humans only use some minute fraction of our brains. Usually it’s around 10 %, but 8 and 4 % are also common. Where did these numbers come from? Literally, from nowhere. The central nervous systemIt’s always been clear as day to me that this whole idea is foolish, but now I’ve found the origin of the myth. We’ll get into that, after exploring the reasons this can’t possibly be true.

Humans use all of their brains

Evolution is about being just good enough. Looking at the end result it doesn’t always seem that way, but it’s true. Our eyes are wondrous pieces of technology, far beyond our capability to invent or build. But they’re also prone to myopia. But that’s almost a metaphoric example, introduced to show that marvel isn’t always perfection.

The reason evolution wants creatures to just get by is purely economic. Natural selection punishes anything that isn’t fit enough, but too fit means investing too much energy, time, and other precious resources into something – this, also, is punished by selection. A cheetah who needed twice as much food as normal to build muscular legs to run faster will have less (or no!) children than its brother who runs more slowly, but also escapes predators.

Our brains total about 1.5 % of our body weight (this varies widely), but consume 20 % of our energy, which means our brains consume 20 % of the calories we eat in a day. This was a radical experiment! Selection would never allow this, unless the brain gave a tremendous return on investment.

The brain is broken into a number of discreet parts with specialized functions. We know this from a long history stretching back to Phineas GagePhinneas Cage, a railroad worker who survived an iron rod more than an inch across and 7 inches long, being blown through his head. Amazingly, the man was able to speak within minutes, and to sit upright while being rushed to the hospital. His friends would later describe him as “not Gage” – his personality was instantly and forever changed. Phineas had trouble walking for much of his following life. In fact, we know a tremendous amount about brain function localization (see Ramachandran), and we know every “piece” has a role to play. Functional magnetic resonance imaging (fMRI) confirms this, even in sleep.

Where did this come from, then?

Although the numbers change, this myth makes very specific descriptions – we use a particular amount of our brain. This leaves open the possibility that the remaining 90 % (or 92 or 96 %, etc) of our brains might allow us to fly, if only we could tap in! So, how do we come to this idea at all, and this number in particular?

In the 1930s, a general scientist named Karl Lashley experimented by cutting lesions into rat brains. Even missing a piece, the rats could survive, and relearn important functions. (This is explained by neuroplasticity.) Having removed many different parts of many different brains in many different rats, it seemed evident that none of them were truly required. On the other hand, if you were to remove all of these pieces from the same brain, the rat it lived in would surely die! Rather, the functions being studied were so vital, that they could be moved from one area to another inside a maleable brain.

We can learn from these experiments that a certain amount of redundancy is built into the system, for safety reasons.

What does it even mean?

What does it mean to use X % of one’s brain, if X doesn’t equal 0 or 100? There are many different ways a person could interpret this, but I don’t think any of them are agreed to? I doubt anyone who repeats this myth even gives it much though.

A typical neuron



  1. […] be so much different from how we know it now.  Sadly, the film’s entire premise is based on the enduring urban myth that we only use 10% of our brain.  The remaining 90% of our brain’s capacity, the film tells us, can be unlocked with the help of […]

    Pingback by Heroes of the East » The Avenging Fist (2001) — July 23, 2008 @ 12:24 pm | Reply

  2. Brilliant!

    Comment by goownsnispap — August 3, 2008 @ 3:49 am | Reply

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