Thursday, December 11, 2008

Book Review - Descartes’ Error: Emotion, Reason, and the Human Brain

My lone class this term was a seminar of the psychology of emotions. We discussed classic and modern literature on evolutionary and mechanistic perspectives of emotions, mood, and feelings. Randy Nesse, a UM psychiatrist and researcher, was our instructor. It was a great class, full of students from varied departments and psychological areas. One of our final assignments was a book review. I read Descartes' Error: Emotion, Reason, and the Human Brain, by Antionio Damasio. Damasio is a renowned neurologist who has written extensively on the human mind, incorporating neuroscience, philosophy, and psychology. I thought I'd repost my brief essay on the book. It's below the fold.

In Descartes’ Error: Emotion, Reason, and the Human Brain, Antonio Damasio tears down the western philosophical view of mind/brain duality, and in it’s place substitutes a lovely body-minded conception of rationality, decision making, and emotion. At the heart of Damasio’s work is a single assertion: the human mind is not separable from the physiological mechanisms that constitute the human body. This, he declares (though somewhat anticlimatically) was Descartes’ error - the rarefaction of the most refined operations of the human mind into a metaphysical spirit, and the subsequent neglect of the importance of somatic processes to the human experience of the self. Damasio inserts emotions and feelings in the middle of the rational decision-making process. Furthermore, Damasio proposes the somatic-marker hypothesis, a synthesis of environment-body-brain-behavioral elements that leads to the distillation of human choice and rationality through experience of affective and bodily feedback. Damasio provides historical and personal patient accounts, exhaustive neurobiological evidence, and some convincing accounts of the importance of body-brain interactions for the generation of behavior. The book is organized into three parts that roughly follow the headings historical context, empirical evidence, and theoretical implications.

“Gage was no longer Gage”

Damasio opens with an account of legendary neurological patient Phineas Gage. Gage was a construction foreman who, durning an excavation explosion in 1848, was impaled through the left cheek with an iron rod. The rod exited through the top of Gage’s head, obliterating a large part of his frontal lobes in the process. Damasio outlines the subsequent treatment of Gage done by John Harlow, in which he documented Gage’s change from an even tempered, clever businessman to an indecisive, irrational, and profane social outcast. Deprived of his orbitofrontal and prefrontal cortices, Gage was never the same; though his other faculties remained unfazed, his decision making, rationality, and emotional expression were profoundly changed. Damasio, in collaboration with his wife Hanna, conducted detailed analysis of the Gage case, and through modern imaging techniques, were able to reconstruct Gage’s skull to infer the damage. Damasio goes on to describe several other historical cases of patients exhibiting Gage-like frontal lesions, as well as personal patients. Damasio’s work with frontal lesioned patients is thoughtfully retold, and it offers a clear insight into the formulation of his ideas about the mind. He develops, as the book progresses, a strong empirical foundation, one that later on, during discussion of his main thesis, the somatic-marker hypothesis, supplies needed authenticity.

In the middle chapters, Damasio outlines, in great detail, the physiology of bioregulatory, emotional, and decision-making events. He provides substantial neurobiological evidence of what he calls perceptual images. Damasio argues that thought is mostly made up of mental representations of knowledge about the world. These images are based on innate tendencies and those acquired though experience. Damasio argues that this coneption of thought, as a series of images, is how the brain produces an integrated mind out of “parcellated” activity. Emotion is integrated with factual information in the process of generating these images to express reasoning and decision making. These central chapters nearly wander too far into monotonous anatomical lecture, but Damasio is careful to reorient himself to one of his central theses: that emotions are an inextricable part of human decision making and rationality.

“To know but not to feel”

A key insight into Damasio’s views on emotion and reason came when he realized that these frontal lobe patients were affectively stunted. They appeared aware of the expected reaction to emotionally charged events, but were unable to express appropriate responses. They exhibited a cold cognition that Damasio related to impairment of their decision-making faculties. As he notes in chapter four “reduction in emotion may constitute an important source of irrational behavior” (pg. 53). Damasio argues that the incorporation of emotion into factual cognitive processes is essential for normal decision making, planning, and rationality.

In chapter seven, Damasio outlines his views on emotions and feelings. Notably, he distinguishes the two, the former very generally being a collection of dispositional changes in the brain/body prompted by certain mental content, the latter being the perception of those changes. This dichotomy is important, as it is in the frontal lesioned patients that emotional feeling is disrupted; they nearly never come to a perception of states of anger, fear, or joy, and this has an impact on their executive functioning. This distinction (one of function and physiology) may prove useful in experimental and clinical settings. In separating the emotion of anger from the feeling of anger, one may be able to parse apart how emotional disorders manifest and persist. Damasio further distinguishes primary emotions (Jamesian, based on ancient subcortical structures) from secondary emotions (built on top of primary emotions, utilizing the highly evolved somatosensory and prefrontal cortices - these are what might be considered “full” emotions, the products of cognitive appraisals and calculations). This discussion of emotional neurobiology illustrates an important application of Damasio’s work; he shows how an understanding of the brain is necessary for a full conception of higher-order cognitive function, and can provide substantial theoretical fuel for such a conception.

Damasio’s emphasis on the importance of subcortical emotional processing provides necessary context for his discussion of basic bioregulation mechanisms (chapter six). Damasio suggests that the bodily systems that control basic regulatory processes also support the production of emotions and feelings, and through their connections with the cortex, are implicated in all human behavior. To Damasio, we wear our evolutionary pedigree on our sleeves (or in our skulls, so to speak), and this provides the basic foundation for his primary theoretical contribution: the somatic-marker hypothesis.

“The organism has reasons that reason must know”

The somatic marker hypothesis is Damasio’s attempt to subvert traditional cognitive accounts of decison making, which posit top-down, “high reason” mechanisms that require logical calculation, conscious weight of costs and benefits, and full consideration of alternatives. Damasio acknowledges that those processes can and do occur, but more often, and perhaps more initially, reasoning comes out of the recall of stored bodily (somatic) feelings. When an event occurs, somatic feedback and a given response are associated with a perceptual image. During future, similar events, these representations are recalled, allowing the individual to narrow the choice of potential decision outcomes. In this way, Damasio intends somatic markers to be efficiency mechanisms; they free up attentional and memory resources so decisions can be made quickly. Damasio further argues that these representations are stored in the ventromedial prefrontal regions of the brain, and their absence in lesioned patients results in impairment of rational thought and decision making. The primary evidence for the importance of bodily feedback in decision making comes from skin conductance experiments, in which lesioned patients fail to exhibit normal physiological reactions to emotional stimuli. Damasio concludes that it is primarily a lack of incorporation of feedback from the body (not just the viscera, as William James contended, but also from the musculature and sensory systems) and affective information in the frontal lobes that disrupts a lesioned patient’s ability to formulate rational decisions, plan, and behave appropriately in social situations.

At its center, Damasio’s idea is a simple one: the body provides vital information that the brain uses to form a perception of the world and to behave in adaptive ways. His argument for the inclusion of emotional processing into a “neurobiology of rationality” is strong, and particularly useful for experimental and theoretical conceptions of the phenomena. The somatic marker hypothesis, while potentially overly complex and biased for negative environmental situations, is notable because it focuses on a holistic, “body-minded” view of human behavior. This is something, Damasio notes, modern cognitive scientists should be keenly aware of.

Damasio successfully pulls the human soul and mind back into the body, and illustrates how in no way does this relocation simplify or diminish it. Damasio’s book is a lucid explanation of what it is to be a human, in all our “fragility, finiteness, uniqueness, and complexity” (pg. 252). We should learn from Descartes’ error, and strive to see each other as what we are, firmly embedded within ourselves.

Continue reading "Book Review - Descartes’ Error: Emotion, Reason, and the Human Brain"!