"In the summer of 1953, a renowned Yale neurosurgeon named William Beecher Scoville performed a novel operation on a 27-year-old epileptic patient named Henry Molaison, drilling two silver-dollar sized holes in his forehead and suctioning out a few teaspoons of tissue from a mysterious region deep inside his brain. The operation helped control Molaison's intractable seizures, but it also did something else: It left Molaison amnesic for the rest of...