Doctors have struggled for centuries to define insanity, and great harm sometimes results when they fail. In the 1970s, Stanford psychologist David Rosenhan and seven other people—sane, well-adjusted members of society—went undercover into asylums around America to test the legitimacy of psychiatry's labels. Forced to remain inside until they'd "proven" themselves sane, all eight emerged with alarming diagnoses and even more troubling stories of their treatment. As the author of Brain on Fire details here, Rosenhan's watershed study broke open the field of psychiatry, closing down institutions, and changing mental health diagnosis forever.