Phineas Gage was truly a man with a hole in his head. Phineas, a railroad construction foreman, was blasting rock near Cavendish, Vermont, in 1848 when a thirteen-pound iron rod was shot through his brain. Miraculously, he survived to live another eleven years and become a textbook case in brain science.

At the time, Phineas Gage seemed to completely recover from his accident. He could walk, talk, work, and travel, but he was changed. Gage "was no longer Gage," said his Vermont doctor, meaning that the old Phineas was dependable and well liked, and the new Phineas was crude and...