Is It True That You Use Only 10 Percent of Your Brain?

Historians have traced the earliest reference to this rumor back to the beginning of the 20th century, when it was perpetuated by self-help gurus promising to expand people’s mental abilities. However, like so many things hucksters have told us, the brain claim is false. “There’s no question,” says Marcus Raichle, a neurologist and professor of radiology at Washington University in St. Louis, “you’re using every little bit of this thing.”

Even when you’re sleeping or just watching TV, your brain is burning a surprising amount of energy for its size. Although your brain constitutes about 2 percent of your body weight, it accounts for 20 percent of the total energy that your body consumes. Scientists know that most of your brain’s energy is used for basic upkeep and communication between neurons. The rest, they speculate, might go toward preparing the brain to receive information by making predictions based on past experiences. For example, instead of scanning your entire fridge each time you want to grab some milk, you can reach directly for the shelf where you last left it—because your brain is working hard to remind you of its location and shoot your hand in that direction. This preprocessing helps you deal with the enormous amount of detail you encounter every day.

You can be certain that all of your brain is working hard, even when you’re not thinking hard. “We should back away from the notion that the only thing the brain is doing is sitting around waiting for something to happen,” Raichle says. “Every piece of it is running full-tilt all the

time.”

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