Do we really use only 10% of our brain?

No. As the Mayo Clinic neurologist John Henley put it, the evidence shows that over a day you use 100 percent of your brain. The idea that humans use only about ten percent of their brains is a myth, and it has been wrongly attributed to many famous people, notably Albert Einstein. Several independent lines of evidence say so.

The first is damage. If nine tenths of the brain sat idle, you could lose most of it with no effect. Instead, almost no area can be damaged without loss of abilities, and even slight damage to small areas can have profound effects. The second is imaging: even during sleep, all parts of the brain show some level of activity. The third is cost. The brain can require up to 20 percent of the body's energy, more than any other organ, while making up only 2 percent of body weight. If most of it were unnecessary, humans with smaller, more efficient brains would have a large survival advantage.

Where did the idea come from? A likely origin is the reserve energy theories of the Harvard psychologists William James and Boris Sidis. The notion spread through the self-help movement of the 1920s, and in 1936 Lowell Thomas gave it a falsely precise percentage in a foreword to Dale Carnegie's famous self-help book. Catchy, precise-sounding and wrong: decades of research mapping functions onto brain areas have found no idle, functionless tenth.