Descartes' Error: Emotion, Reason, and the Human Brain

Damasio's central claim is that emotion and feeling are indispensable to rational thought, and that the mind cannot be understood apart from its intimate relationship with the brain and body [citation:9]. He explicitly rejects the Cartesian separation of mind from body—the error named in the title—which has shaped Western science by treating reason as a faculty that can operate independently of emotion and biology. Damasio argues that rational decisions are not the product of logic alone; they require the support of emotion and feeling. Drawing on neurological patients with prefrontal damage who show intact intellect but impaired judgment, he demonstrates that when emotion is absent, rationality itself breaks down [citation:1][citation:3].

The book introduced the somatic marker hypothesis, Damasio's proposed mechanism by which emotions guide decision-making. The hypothesis holds that bodily feedback—the 'somatic marker'—from secondary emotions acts as a signal that prevents decision-makers from contemplating courses of action with bad consequences [citation:5]. In experiments with the Iowa Gambling Task, normal subjects showed anticipatory galvanic skin responses before consciously realizing which decks were risky, while patients with prefrontal damage showed no such responses and continued to choose disadvantageously [citation:5]. The hypothesis was designed to explain how emotion aids reason, and it has become one of the most influential theories in neuroeconomics and decision science [citation:16].

The reception was largely positive, though not uncritical. Chris Frith, reviewing in Perception, called it 'an immensely attractive hypothesis' and recommended it to anyone wanting to understand the excitement of brain research, though he found parts 2 and 3 less successful than the opening chapters on Phineas Gage and was unconvinced by some of the argumentation [citation:9]. The book was praised for its engaging style and its bold challenge to traditional views of rationality. One academic review noted that Damasio 'condensed an avalanche of neuroanatomical and neurophysiological data and presented it in readable form,' while also pointing out that some classic works on the limbic system were overlooked [citation:3]. The book became a bestseller and is widely credited with helping to legitimize the study of emotion in neuroscience [citation:7].

Descartes' Error sets the stage for Damasio's later explorations. The Feeling of What Happens (1999) builds directly on its foundation, extending the argument from emotion and reason to the problem of consciousness itself. In the later book, Damasio proposes that consciousness arises from the brain's mapping of the body's internal states, distinguishing a transient core self from the autobiographical self [citation:6][citation:12]. The somatic marker hypothesis remains a reference point throughout. Looking for Spinoza (2003) further develops the embodied perspective, arguing that Spinoza anticipated Damasio's view that mind and body are inseparable aspects of a single substance. The trajectory of Damasio's work is thus a sustained elaboration of the embodied mind thesis first fully articulated in Descartes' Error.

A frequent misconception is that Damasio claims emotion should replace reason or that feelings are always reliable guides to decision-making. In fact, his argument is more precise: emotion is necessary for reason, but it does not guarantee good decisions. The somatic marker hypothesis describes a mechanism that can bias choices toward advantageous outcomes, but Damasio acknowledges that emotional signals can also be miscalibrated or inappropriate. Another misreading treats the book as claiming that all decisions require conscious emotional experience; Damasio's experiments suggest that somatic markers often operate unconsciously, influencing behavior before the person is aware of any feeling [citation:5]. The book also does not claim that patients with prefrontal damage have no emotions at all, but rather that their emotional responses to complex, real-world situations are impaired while basic emotional reactions may remain intact [citation:3].

The hypothesis has been widely influential but also contested. A 2019 review in Escritos de Psicología noted that 'various studies, for and against, have been written, without a verdict' since the hypothesis was formulated [citation:16]. The review concluded that the somatic marker hypothesis's greatest value has been to end the brain-body duality, but that the hypothesis alone is insufficient to sustain the claim that decision-making proceeds primarily from what we feel; decision-making is a more complex physical-emotional-rational process [citation:16]. Some researchers have found mixed results in the Iowa Gambling Task, and the precise role of the amygdala versus ventromedial prefrontal cortex continues to be debated. However, the broader claim that emotion is integral to rational decision-making is now widely accepted in neuroscience.