His findings were clear and reasonably consistent. “One can remove,” he wrote in 1824, “from the front, or the back, or the top or the side, a certain portion of the cerebral lobes, without destroying their function.” For mental faculties to work properly, it seemed, just a “small part of the lobe” sufficed.
Thus the foundation was laid for a popular myth: that we use only a small portion — 10 percent is the figure most often cited — of our brain. ...
But Flourens was wrong, in part because his methods for assessing mental capacity were crude and his animal subjects were poor models for human brain function. Today the neuroscience community uniformly rejects the notion, as it has for decades, that our brain’s potential is largely untapped.
--Gregory Hickok, NYT, on the genesis of the myth