One of the earliest treatments for mental illness was developed in Neolithic times, more than five thousand years ago. In a process known as trepanning, Stone Age surgeons would use a small tool to bore a hole in the skull of their patients in order to release the evil spirits believed to cause mental illness. Since that time, people have developed hundreds of treatments that today seem cruel or bizarre. For example, in 1276, Pope John XXI, the author of several medical treatises, suggested that eating a roasted mouse could cure anxiety. In the seventeenth century, French and British doctors experimented with transfusing the blood of sheep into their patients, thinking the blood of a docile creature "might tame their mad passions." In 1667 an "insane" Englishman named Arthur Coga received a transfusion of twelve ounces of sheep blood, but the treatment did not help greatly. Well-known diarist Samuel Pepys...