"Although I cannot tell for certain what sparked my interest in the neural underpinnings of reason, I do know when I became convinced that the traditional views on the nature of rationality could not be correct." Thus begins a book that takes the reader on a journey of discovery, from the story of Phineas Gage, the famous nineteenth-century case of behavioral change that followed brain damage, to the contemporary recreation of Gage's brain; and from the doubts of a young neurologist to a testable hypothesis concerning the emotions and their fundamental role in rational human behavior. Drawing on his experiences with neurological patients affected by brain damage (his laboratory is recognized worldwide as the foremost center for the study of such patients), Antonio Damasio shows how the absence of emotion and feeling can break down rationality. In the course of explaining how emotions and feelings contribute to reason and to adaptive social behavior, Damasio also offers a novel perspective on what emotions and feelings actually are: a direct sensing of our own body states, a link between the body and its survival-oriented regulations, on the one hand, and consciousness, on the other. Descartes' Error leads us to conclude that human organisms are endowed from the very beginning with a spirited passion for making choices, which the social mind can use to build rational behavior.