Do we really only use 10% of our brain?

It’s one of the most repeated “facts” on the internet: we only use 10% of our brain, and the rest is waiting to be unlocked. It shows up in films, ads and a lot of motivational videos. So let’s check it the way RealUp does, one sentence at a time.

Fact check4 sentences

We only use 10% of our brain.False

Brain imaging shows activity across the whole brain over the course of a day, even during sleep.

Your brain uses about a fifth of your body’s energy.Supported

About 2% of body weight, about 20% of the oxygen and calories the body uses at rest.

You use your whole brain for everything you do.Oversimplified

Over a day almost every region is active, but not all at once and not for every task.

Everyone should train their brain every morning.Opinion

Why the 10% idea doesn’t hold up

Scans show a busy brain. Brain imaging finds most areas active over a 24-hour period, including during sleep. As one Mayo Clinic neurologist told Scientific American: “over a day you use 100 percent of the brain.”

Even simple things are big jobs. Pouring a cup of coffee draws on seeing, planning a movement, balance and fine control, spread across many parts of the brain at once.

The brain is expensive. It makes up about 2% of body weight, but at rest it uses about 20% of the oxygen and calories the body burns. An organ that costly, with nine tenths of it idle, would make little sense.

Neurons don’t sit around. Some fire hundreds of times per second. And when parts of the brain are lost, for example after surgery in early childhood, the rest rewires to take over. That’s a brain using what it has, not one keeping 90% in reserve.

So where did 10% come from?

Nobody knows for sure. One common trail leads to the psychologist William James, who wrote in 1907 that people use only a small part of their possible mental resources. He was talking about untapped potential, not unused brain tissue. Somewhere along the way, “potential” turned into a percentage.

The takeaway

You use all of your brain, just not all of it at the same time for the same thing. The claim sounds scientific because it has a number in it. That’s exactly the kind of sentence worth marking and checking.

Sources

1. Raichle, M. E. & Gusnard, D. A. (2002). Appraising the brain’s energy budget. PNAS 99 (16).
2. Scientific American (2008). Do people only use 10 percent of their brains?
3. MIT McGovern Institute (2024). Do we only use 10 percent of our brain?