On a Monday morning at a home for the elderly in Cologne, Germany, a nurse asked 73-year-old Mr. K. about his weekend. “Oh, my wife and I flew to Hungary, and we had a wonderful time!” he replied. The nurse paused—Mr. K.'s wife had passed away five years ago, and he had not left the home in months. Was he trying to impress her? More likely, Mr. K. was confabulating, a phenomenon in which people describe and even act on false notions they believe to be true.