This functional magnetic resonance imaging of a brain, provided courtesy of the Albert Einstein College of Medicine, shows activity in the ventral tegmental area (VTA).AP Photo/Albert Einstein College of Medicine, Lucy Brown

Reading this, you’re probably using, what … 10 percent of your brain? Funny how that notion took hold—that we use a tenth of our brain at any given time—because there’s no actual evidence for it, the Conversation reports.

The idea may date back to psychologist William James, who wrote in 1907 that we use “only a small part of our possible mental and physical resources,” and a foreword to Dale Carnegie’s How to Win Friends and Influence People that loosely quoted James as saying that “the average person develops only 10 percent of his latent mental ability.” Now, products exist to “unlock the other 90 percent” and a new thriller, Lucy, shows Scarlett Johansson taking drugs that enable her to use all 100 percent of her brain.

But, as the Atlantic reports, scientists point out that the brain is an organ packed with living neurons that are always up to something. Brain scans that show only a small active portion of gray matter “lighting up” may confuse people, one neuroscience professor points out, because they show only the brain’s major activities, not all of them.

Yet “those kinds of ideas self-perpetuate,” he says. One possible basis for the 10 percent notion: The brain has almost 100 billion neurons, which are outnumbered roughly 10:1 by “glial” cells that keep the brain working.

“In other words,” the Conversation notes, “neurons are only 10 percent of our entire brain.” (See how lack of sleep can fry brain cells.)

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