Kurt Fischer, Ph.D.'s  picture
Kurt Fischer, Ph.D.
Charles Bigelow Professor of Human Development and Psychology and Director of the Mind, Brain, and Education program
Harvard Graduate School of Education

We Use Only 10 Percent of Our Brain

L-rn learning myths

Misunderstood research has led to this misunderstanding

We’ve all heard this one, right? It seems to jibe with that suspicion that we don’t live up to our potential. If we used even 12 percent of our brain, much less 35 percent, things would be different! This myth is an especially absurd one, says Kurt Fischer, Charles Bigelow Professor of Education at Harvard, and director of Mind, Brain, and Education at the Harvard Graduate School of Education. Read on to find out why…

LearnNow: All right, so dispel this 10 percent myth for us!

KF: This one is so easy to knock out. It’s just totally wrong. In my class, we run a little movie that shows what happens in the brain when you see a word flash on a screen. Let’s say the word is “dog.” Using a highly accurate imaging instrument called a magnetoencephalogram sensor (MEG), we can see what happens inside your brain when the word appears. It’s not just areas where visual (the image of a dog) and verbal (the word “dog”) activities take place. Almost all of your brain lights up like a symphonic pattern. It starts in back where the visual cortex is and it moves forward, and cycles back and forth.

LearnNow: Almost all of the brain is involved in an exercise even this simple. So why has the 10 percent myth persisted?

KF: Partly it’s due to what we call the “subtractive method” that’s traditionally been used in most brain research. Neuroscientists wanted to see what happens when you see a word or a shape. They would use two conditions: In one, they would measure what happens when the word is flashed on a screen (experimental condition). For the other, they would measure what happens when, say, a meaningless blob shape is flashed up (control condition). Then they would subtract the brain activity in the experimental condition from the control condition. The result is usually one or a few areas of the brain that distinguish the two conditions. When you subtract like this, it looks like not much of the brain is involved, but it’s just been subtracted out for research purposes. This methodology continues to be widely used in neuroscience.

LearnNow: So that methodology has its purpose. But it also made us think small picture, not big picture?

KF: Yes, that’s right. It started to change a few decades ago with the landmark studies by Washington University neurologist Marc Raichle. He said wait a minute, shouldn’t we look for what happens across the brain, in all its many parts? And he discovered that many networks existed, such as the default network. It turns out that when you’re in a quiet alert state, a bunch of the brain is percolating along on default. Now there is a major shift happening in the whole field in neuroscience toward a focus on what we call networks— parts of the brain that commonly work together rather than just one or two specific locations.

LearnNow: Has other research inadvertently fed the 10 percent myth?

KF: Yes, it’s also based on misunderstood research, especially Karl Lashley’s work at Harvard in the 1930s and 1940s. He was researching brain damage. So he took rats with a lot of experience moving through a particular maze, and watched to see if they could still move through it once they had suffered damage to their brains. It turns out they could; even if they had trouble walking, they could stumble to get to where the food was. You could destroy much of their brain and they could still function—so some extrapolated you only “needed” 10 percent of your brain. Wrong conclusion. Notice, for example, that with much of their brain destroyed, they could not even walk readily through the maze.

LearnNow: There’s an evolutionary case to be made against the 10 percent falsehood, right?

KF: Right. Evolution prizes efficiency. Like all other organs, our brain has been shaped by natural selection. While the brain only weighs 2 percent of the total body weight, it uses 20 percent of the total energy. Thus, brain tissue is metabolically expensive to grow and run. A brain that works at 10 percent capacity, wasting so many resources, would not be worth the high costs, and therefore human beings with their large brains would have already been excluded from the gene pool.

LearnNow: So how efficient is the brain, then?

KF: There are some fascinating findings on efficiency. A lot of people think, the smarter you are, the more active your brain is. But in fact, if you are really good at something, your brain shows less activity when you perform a task within your expertise than when a novice performs the same task. Want to see the brain massively light up? Try learning something new.

LearnNow: But has this efficiency effect also fueled the 10 percent myth?

KF: We now know that efficiency is characteristic of brain functioning. One of the great research surprises of the last 30 years in brain development is that the brain prunes (or gets rid of) circuits that are not efficient. We used to think any loss of brain tissue was bad. But pruning is one of the brain’s most important processes. And so that 10 percent myth comes back into play. Here’s the deal: You’re never using such a small portion of your brain as 10 percent—but you are using less when you’re really good at something.

LearnNow: Okay, so an old research method, misinterpreted research conclusions, plus lack of understanding of evolution and efficiency have led to the 10 percent myth. Now that you’ve set us straight, I have to ask: How much of your brain do you use?

KF: [Laughs.] I use most of it most of the time! Like all of us.

Learn More:

“Understand Your Teen’s Brain,” by Timothy Myers

Related Reading:

Neuroscience for Kids: Do We Use Only 10 Percent of Our Brains? Neuroscience for Kids, Eric Chudler, department of bioengineering, University of Washington

“Inside the Brain of a Beatboxer,” BBC News story about the differences between the brains of an expert and amateur