Descartes’ Error: Emotion, Reason, and the Human Brain (published in 1994 and revised in 2005) is neuroscientist Antonio Damasio’s first full-length work on the physiology of rational thinking. It posits that human emotions play a crucial role in guiding (and occasionally hindering) decision-making. The author refers to this as his “somatic-marker hypothesis” (12). As the title implies, Damasio rejects the Cartesian concept of mind-body duality, a philosophical notion (which Descartes championed) that affected the development of neuroscience in the 20th century. Instead of developing alongside neuroscience, research on human emotions and feelings was decoupled from biology and relegated to the realm of psychology and psychiatry. Descartes’ Error draws on two decades of clinical evidence from patients who, after experiencing cognitive alterations, developed problems in their decision-making and defects in their capacity to feel emotions.

Damasio’s unconventional findings invited further research on the physiology of human emotions. Despite its novel argument, Descartes’ Error received critical acclaim from lay audiences and experts alike.

This summary is based on the 2005 edition.

Summary

Descartes’ Error is separated into three parts. Part 1, which includes Chapters 1 through 4, uses the famous case of Phineas Gage to introduce the subject of neurobiology. Damasio then places subsequent cases that he studies—patients who sustained damage to the prefrontal cortex that altered their disposition and emotional experience—in his “Phineas Gage matrix.” Beginning with Phineas Gage himself, Damasio points out that people belonging to the Phineas Gage matrix all retain their intelligence yet seem incapable of making advantageous decisions when confronted with inter- or intrapersonal situations. More importantly, their capacity to feel emotions decreases. This leads Damasio to suspect a close relationship between emotion and reasoning—a relationship previously unexplored due to the conventional belief that emotions hinder rationality. Chapter 1 introduces Phineas Gage and the incident that altered his behavior. Chapter 2 explores the literature surrounding Gage and its implications on the interconnected nature of emotion and reasoning. Chapter 3 introduces Elliot, a patient referred to Damasio who sustained brain damage in the same area as Gage and developed similar symptoms. Chapter 4 explores other known cases of prefrontal cortex damage in patients of different ages to discuss how emotion might affect the development of proper social behavior. Throughout Part 1, Damasio’s main focus is delineating the symptoms and conditions of patients who belong in the Phineas Gage matrix.

Part 2, which includes Chapters 5 through 8, attempts to formulate a theory on the connection between emotion and reasoning. This culminates in Damasio’s somatic-marker hypothesis. Chapter 5 defines the neurobiological terms that the author uses in Descartes’ Error. Chapter 6 posits that the body came first in the evolutionary process, whereas the mind developed to enhance the body’s survival. Damasio theorizes that consequently, the mind is primarily concerned with monitoring the state of the body. Chapter 7 defines primary and secondary emotions as modalities that enhance an organism’s survival by expediting and biasing the decision-making process. Chapter 8 properly defines the somatic-marker hypothesis and postulates that the body marks an emotion to a particular situation to allow the organism to anticipate and prepare for similar future situations and thus help ensure better chances of survival in a complex environment. Rationality and decision-making therefore require feedback from the body in the form of somatic markers to function properly.

Part 3, the final part of the book, focuses on testing the somatic-marker hypothesis on Elliot and other individuals in the Phineas Gage matrix and then comparing them to a control group. In Chapter 9, Damasio explores the two main tests that allow him to confirm his theory’s plausibility: the skin conductivity test and the gambling experiments. They show that patients like Elliot take significantly more risk than control groups due to an inability to anticipate negative outcomes—which in turn results from their stunted ability to feel emotions. Chapters 10 and 11 extrapolate on the implications of the somatic-marker hypothesis and conclude that the concept of consciousness and selfhood are intrinsically tied to biology, unlike the Cartesian theory of mind-body duality. Damasio concludes that the fragility of human individuality does not compromise its beauty. He urges neuroscientists to continue research on the connection between reason and emotion.