One of the book’s main themes, as evident in its title and subtitle, is the impact of the Cartesian concept of mind-body duality on the field of neuroscience. The book’s opening paragraphs point to a gap in knowledge on the topic of emotions in neuroscience. Instead of seeing them as part of human biology, scientists relegated emotions to the field of psychology. As a result, people like Elliot, who are perfectly intelligent yet have a compromised sense of self, have difficulty obtaining disability benefits. Psychological evaluations cannot detect their conditions, and evaluators downplay their problems. This is partly due to the widespread belief in the incorporeality of the human mind, a philosophical perspective that Descartes championed.

The mind-body duality theory posits that the body is simply a machine that responds to stimuli while the mind (or spirit) is immaterial. When inappropriate emotions do not cloud the mind, humans are capable of high reason. This philosophical view became popular in Descartes’ time, and Damasio insists that its impact stretched to the medical world. The author believes that Cartesian thought negatively influenced Western medicine and retarded its development by several decades.