Since its introduction in 1846, anesthesia has allowed for medical miracles. Limbs can be removed, tumors examined, organs replaced—and a patient will feel and remember nothing. Or so we choose to believe. In reality, tens of thousands of patients each year in the United States alone wake up at some point during surgery. Since their eyes are taped shut and their bodies are usually paralyzed, they cannot alert anyone to their condition. In efforts to eradicate this phenomenon, medicine has been forced to confront how little we really know about anesthesia’s effects on the brain. The doctor who may be closest to a solution may also answer a question that has confounded centuries’ worth of scientists and philosophers: What does it mean to be conscious?