What using 10% of your brain would be like

There's been a lot of hubbub about this film Lucy and how there's some aspect of the movie where someone is using "more than 10% of their brain". I don't know anything about this movie, so I can't say for certain what they are trying to get at... but a movie called Limitless also had a similar premise of "unlocking more than 10% of your brain's power".

As any Google sleuth will find out, you use more than 10% of your brain. You actually use your entire brain, barring any brain damage.

But what would 10% of your brain actually look like? What would you be able to use?

Brain facts

Your brain (the human brain) is about 3 lbs (various internet sources range between 2.5 lbs and 3 lbs -- the brain in our lab weighs around 3 lbs).

On average, it is 5 inches wide (from "ear-to-ear"), 6.5 inches long (from "forehead to the back of the head"), and 3 inches tall (from "the bottom to the top").

We divide the brain many different ways -- by evolutionary characteristics (hindbrain, midbrain, forebrain/cerebral cortex); by functionality (frontal lobe, temporal lobe, parietal lobe, occipital lobe); by physical landmarks (left brain, right brain; cortical, subcortical); by specific areas (Broca's area, tempero-parietal junction, anterior cingulate cortex, etc); and manymanymany other ways.

Brain myths

"We only use 5%/10%/20%/X% of our brain." Nope! We use all of it.

"There's a 'learning'/'math'/'music'/'talent'/'X' part of your brain." Nope! The brain works in a network -- many areas of your brain integrate and contribute towards one (or any/all) of the experiences and actions you have in your life.

What would using only 10% be like?

If you aren't convinced and still believe the hype, let me drop some knowledge:

If we take 10% of all the dimensions we end up with:

Brain weight: 0.3 lbs
Brain dimensions: 0.5 in X 0.7 in X 0.3 in

Note: as stated in the comments, this isn't mathematically correct. But then again, the entire myth isn't correct. 

If shrunk down, it would look something like this (this is completely inaccurate, but it's close.)


From this view, many neuroscientists could pick out areas that are seemingly "10%" of the surface area of your cortex. I've chosen a few to elaborate on...


If you only could use 10% of your brain, you could only use one of these two areas. Red is known as Broca's area and blue is known as Wernicke's area. Broca's area is used for speech production. If you've ever met someone who had Broca's aphasia, which is an impairment to this area, they have troubles trying to clearly verbalize what they want to say -- sometimes coming out like stutters or single words. Wernicke's area is used for speech processing, or being able to comprehend and integrate what you want to say. People with Wernicke's aphasia sometimes produce very nonsensical sentences -- their Broca's area is fine, so it sounds like a normal sentence, but the meaning is jumbled and incomprehensible. This is sometimes known as "word salad".

YOU COULDN'T DO ANYTHING ELSE. In fact, you wouldn't even be able to talk in order to make use of these speech areas (we'll get to that in a second).


If you could only use 10% of your brain, you would only be able to use a part of your cerebellum. Your cerebellum is involved with motor movements -- both fine movements (like finger-pointing or wiggling) and gross movements (like swinging your arms or walking at a pace). The part highlighted in red here could represent only being able to use fine or gross movements on the right side of your body (for many functions, your left brain will control your right side and your right brain controls the left side; this is known as contralateral control).

Again... YOU COULDN'T DO ANYTHING ELSE. Sight? You wouldn't have it. Ability to plan? Nope. Hearing? Hahahahahaha..... no.


If you only could use 10% of your brain, you could only move or feel (not both -- either/or) particular fine motor or sensory features. In this crude highlighting, I've determined you can choose to either move or have sensation through one of these combinations: hip/knee, hand/wrist/fingers, neck/eyebrow ridge/eyes, voice/lips, or tongue.

And, as mentioned before, only on one side. You want to move your hands on both sides? Sorry, that's 20% of your brain. Feel through the touch of your knee? You'll have to choose either your left or right knee.

And once again, YOU. CAN'T. DO. ANYTHING. ELSE. Again, no sight. No hearing. You would be able to vocalize noises but you have no use of Broca's and Wernicke's areas in order to produce anything meaningful. You could move one of these areas but you have no ability to walk. We haven't even discussed bodily functions or how you would be able to keep your heart beating and lungs respiring. Did you think that stuff was regulated magically by something not connected to your brain?

We use more than 10% of our brains. Stop believing we use less than all of it.

5 thoughts on “What using 10% of your brain would be like”

  1. cairnsh says:

    When you scale all three dimensions down by 10, you wind up with something that has 0.001 times the mass and volume - so 0.1%, not 10%.

    For example, a litre is 0.1 m x 0.1 m x 0.1 m, and a cubic centimetre is 0.01 m x 0.01 m x 0.01 m. All of the dimensions are ten times smaller, but a litre is not 10 ccs.

    I can't say this any more politely. I'm only barely holding back a rant about scientists that think nonsense explanations are good enough for the layman.

    And you know, the premise of this post is kind of ridiculous too! I always understood this urban legend as something about a bunch of reserve capacity, not "humans don't need the motor cortex, wake up sheeple."

    1. Nick Wan says:

      Good points.

      This post was fun to write, regardless of accuracy. I'll make an edit though, thanks.

      The myth of 10% can be cut however you want, but it's just not true in any way you want to cut it. Another way you can think of it would be in terms of neurons. The average brain has 100 billion neurons. If we use only 10 billion, what's the other 90 billion doing? The body has a pretty quick "use it or lose it" temperament to it -- if something isn't being used, it gets cut out. No reserves or boosts or anything like that.

      1. cairnsh says:

        I feel like I can make a counterargument, so I'm going to try and be a devil's advocate. I was mad earlier, but this comment is in a more fun spirit. I hope it is okay. 🙂

        If there were that many unused neurons, they would atrophy. Ok, what if all the neurons are firing, but the average brain has considerable unused capacity in some sort of machine learning sense? We pretend we can quantify how many neurons it takes to be good at something, and we say that the average person is at a tenth of their limit.

        This is a picture where an "undertrained" skill just uses the neurons in an inefficient way. They fire, so they're not going to atrophy, but there is still a lot of reserve capacity.

        Is there an easy way to disprove that? I guess you could say something about evolutionary pressure, but maybe there's some other reason why you would want to have more neurons than strictly necessary - maybe having a lot of neurons makes it easier to remember a skill without practicing it constantly.

        1. nickwan says:

          Neural efficiency hypothesis (which is actually something I study!) is a good way to think about how brain and behavior respond in the face of a task where expertise may be needed.

          Another myth once before was "the more brain areas you use, the smarter you are." Which is similar to the 10% myth and also the Einstein myth. With neural efficiency hypothesis, it's actually "smarter," or rather more efficient, to use less resources to do a task.

          When we learn a new task, behaviorally we are usually not great at it and neurally we are not efficient. Over time, with practice, both those things become more efficient.

          You talked reserve capacity. It's hard to define capacity that is being "reserved" because if you are efficiently using your brain, you actually don't need unnecessary networks activating. Therefore, the idea of "reserved" or "extra" areas are really better defined in this case as "unnecessary".

          Easy way to disprove this are comparing novice task doers vs expert task doers. Babiloni and his collaborators have researched a good deal on neural efficiency in terms of cognitive performance -- with chess players, taxi drivers, Olympians, pilots, and a few other populations.

          We can also think about things in terms of neural plasticity. When we lose function to an area, say hearing, adjacent areas sometimes begin using the neural connections that were evacuated, which could be "reformatted" to sensory, motor, or other functions. Again, if the area is not being used fully, atrophy occurs. But also, plasticity occurs.

  2. Adam says:

    This was an interesting read, however it seems to be looking at the theory incorrectly. Shouldn't we look at this from an efficiency aspect rather than mass perspective? In simple terms rather than saying if we actually did only use 10% of our brain we couldn't even talk, surely we should be considering that we all use 100% of our brain but very inefficiently thus only outputting 10% of the mental capacity we could be in charge of? I am pretty sure that this is the way most science fiction movies look at it.

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