Critique of Cartesian dualism I: Antonio Damasio’s somatic marker hypothesis

To call René Descartes a father of Western philosophy is no exaggeration. His contributions to philosophy and mathematics dominate our thought, ranging from his famous declaration ‘I think, therefore I am’ to his construction of the Cartesian coordinate plane. But what were once considered foundational paradigms are becoming increasingly becoming frustrated by advances in contemporary neuroscience. From Antonio Damasio’s Descartes’ Error, to Daniel Dennett’s disfigurement of the Cartesian theater in Consciousness Explained, to the common neurologist’s knowledge of the banality of the pineal gland, modern sciences have begun to push against Descartes’ philosophy. This essay series will discuss recent developments in neuroscience and psychoanalysis, and elaborate on a common thread that reveals widespread epistemological breaks with Descartes. What does this break mean for the future of Western philosophy in general, and cognitive sciences in particular?

Damasio’s somatic marker hypothesis

In our era of quantum weirdness, psychedelic experimentation, and an embrace of Eastern practices, the foundational tenets of Western philosophy are being shaken and reexamined. A book with the title Descartes’ Error, then, should be of particular importance to anyone with a feel for the pulse of our shifting era. Antonio Damasio doesn’t disappoint: the central theory of his work, the somatic marker hypothesis, should certainly be considered a strong empirical case against the assumptions of classical Western thought.

What is Descartes’ error? Those familiar with psychology or neuroscience should immediately be reminded of the Cartesian theater, an intuitive but ultimately erroneous conception of the soul as a kind of seat of phenomenal experience. Daniel Dennett has spent a considerable portion of his work fighting against this idea, using findings from cognitive science, neurobiology, and the technique and cutting logic of a philosopher. Today, the relatively unsophisticated function of the pituitary gland is a lasting testament to Descartes’ blunder; he hypothesized that it might be the location of this so-called seat of conscious experience.

But the error which gives Damasio’s book its title is a different one from the French philosopher. It is Descartes’ categorization of rational thought as distinct from affect, which was considered to originate from a more basal, primitive portion of the mind. This distinction carried with it the appealing anthropocentric notion that rational deliberation — “high reason” — was not only separate from emotional processing, but separate from the body altogether: the hallmark of the human spirit, that immaterial substance of the soul. In Descartes’ dualist conception of mind and body, reason was given a space firmly in the place of mind, hence his distinction between the res extensa (extended, mechanical part) and res cogitans (thinking part).

It is against this philosophical disposition that Damasio introduces his somatic marker hypothesis. His rich experience with neurological patients forms the basis of his introduction, where he elaborates on the clinical symptoms of those with damage to the ventromedial prefrontal cortex (vmPFC), a region of the brain located just behind the eye sockets. These patients appear largely normal from a typical, psychological point of view: neither their IQ is diminished, nor their pattern-recognition skill, nor their emotions, nor even the ability to discern ethically right decisions from wrong decisions. And yet these individuals often lead remarkably poor personal lives, owing to a propensity for impulsivity, poor decision making, and diminished future planning. What could explain this discrepancy?

Damasio theorizes that the ventromedial frontal cortex is a relay center between mental representations and secondary emotions. Here, secondary emotions should be distinguished from primary emotions. The latter are intense feelings whose neural correlates are largely pre-programmed: think of the intense disgust that we all feel upon encountering a rotten egg or decaying carcass. This response is not contingent on training or stimulus-response association; it exists by virtue of circuitry which has persisted because of its innate advantage to the species. On the contrary, secondary emotions are developed through the course of experience, and comprise associations between a given mental representations and a certain emotional response … In patients with damage to the vmPFC, then, mental representations conjured up by rational deliberation are unable to incite their appropriate emotional contents, and decision making throughout their lives becomes dysfunctional as a result.

Here we arrive at the definition of a somatic marker. What does it mark? A specific mental representation that is encountered through the process of rational thought. Why is it somatic? Because it involves an emotional response whose substrate is the body (think of the connections that the hypothalamus, as an originator of emotional response, makes with the rest of the body: vasoconstriction, perspiration, and so on). When a mental precept can trigger a kind of as-if loop, which Damasio calls a dispositional representation, its contents can begin to bring about the physiological response that is consistent with a specific emotion. Therefore, when mental precepts are being compared, contrasted, selected, and singled out, somatic markers guide the process by providing emotional salience to certain alternatives. We are reminded again of the opposition of this theory to Descartes’ assumption that rational deliberation is in a realm of its own: as if the frontal cortex, that locus of pure reason, is completely separated from the sources of emotional response. Damasio rejects this notion: his rejection is in the form of the somatic marker hypothesis, and his proposed bridge between reason and emotion lies in the vmPFC.

In this sense, the somatic marker hypothesis can be seen as an affirmation of Kant’s primacy of practical reason over theoretical reason. For it appears that every so-called rational theory on the nature of reality, which takes as its ultimate manifestation a formal, systemized philosophy, may be influenced by the kind of emotional linkages Damasio calls somatic markers. This may be a neurobiological corroboration to the anti-philosophical notion that every theory is contingent on a practico-ethical engagement: pure reason can never be divorced from a particular thinker’s practical, subjective impression of his individual life. Here, we can reread Johann Fichte’s statement “What philosophy one chooses depends on what kind of man he is” as prescient to Damasio’s empirical claim “What conclusion one arrives at in the course of so-called purely rational deliberation depends on what somatic markers, through the course of experience, have refined and prioritized his mental representations.”

Finally, we can begin to discuss the ramifications of Damasio’s theory on the concept of robot brains or minds. For robots can certainly produce, deliberate, and select representations with the degree of algorithmic rigor that is accessible by the human mind — in fact, it does so with an efficiency that surpasses our capabilities. This kind of activity is best described using David Chalmers’ category of A-consciousness as opposed to P-consciousness. Whereas P-consciousness describes subjective experience, the Nagelian what-it’s-like-to-be a living organism, A-consciousness is a more abstract qualification that deals with the ability to retain and manipulate mental representations. A-consciousness also suggests a kind of global-access (indeed, one prevailing theory of self-reflexive consciousness takes the name of global-access theory, which maintains that self-reflexively conscious content is that which can affect global change on any other mental precept). For this reason, robots have tentatively been categorized as machines which are capable of A-consciousness but not P-consciousness.

Of course, Damasio’s theory now casts doubt over what the nature of such an exclusively A-conscious being would be. What if, far from simply being marked by somatic correlates, the diachronous process of thought itself is driven by underlying mechanics of affect? This would disqualify robot minds from ‘thought’ proper, as even the most complicated artificial neural networks are not driven by affect (as far as we can tell: they are programmed to maximize given output parameters, etc). This intersects with the so-called ‘hardware question’ of consciousness, which asks whether there is a fundamental substrate of phenomenal experience. In other words: is there something unique about the material configuration of our brains (consisting of neurons, neurotransmitters, etc) that is necessary for consciousness? Or could our experiences of pain, pleasure, and redness be experienced by a metallic robot of adequate complexity? wetware nick bostrum

Damasio’s somatic marker hypothesis isn’t the only one which elaborates on a link between ideational representations and affect. V. S. Ramachandran’s research on patients with Capgras syndrome has lead to his proposal of what he calls the inferior thalamic (IT)-limbic disconnection hypothesis. Capgras syndrome is a rare and bizarre affliction whereby patients will report that their loved ones have been replaced by imposters. In order to investigate what neural mechanism is involved in this strange psychological case, Ramachandran conducted several experiment on a Capgras patient named DS. The first of these involved a skin conductance test whereby DS’s unconscious emotional responses to familiar and unfamiliar faces was assessed. Compared to controls, DS did not exhibit what Ramanchandran calls the emotional ‘glow’ which is typically observed when one sees a familiar face. In another experiment, DS was largely incapable of gauging whether a model was looking off-center or directly at him. But interestingly, DS communicated that the same model had changed three times during the course of the study. It appears that DS’s ‘imposter syndrome’ caused him to partition the identity of the same person multiple times.

Ramachandran interpreted these results as a deficit in IT-limbic connections, which are normally involved with applying emotional salience to visual representations. According to this theory, what is causing DS to conflate his loved ones with imposters (as well as identify the same model as three different people) is a discontinuity between a given visual representation and its appropriate affect. Ramachandran believes that the continuity in affect between the same visual representation is important to constructing an identity: without the ability to retrieve the ‘old file’, the brain creates a new slot for the experience. Thus, when DS looks at a familiar face but does not experience the affect which would normally accompany it, his explanation is that an imposter must be afoot: he does not believe that it could be the same individual.

All this is to say that the link between intellect and affect is much more substantial than we normally think. Day to day, we might consider the function of pure reason and emotions to be distinct; we’re often told to separate the two when it comes to making ‘clear minded decisions’ and so on. In Damasio’s book, the error which Descartes is charged of making is precisely this position that reason can, and perhaps should, be divorced from subjective conditions of preference, passion, etc.

A scene from one of my favorite TV shows, Psych, will make an nice example of the relationship between semantic versus emotional processing. The hyper-vigilant ‘psychic’ detective Shawn Spenser has conducted a breaking-and-entering and quickly becomes a person of interest. He is hooked up to a lie-detector test and must find a way to conceal his lies. In order to accomplish this, he employs a beautiful strategy: he recreates the events in his mind, but uses ambiguous words in order to describe these memories. Thus, the words he conveys do not incriminate himself in any way, and yet they cannot be detected by the physiological readings of the lie detector because Shawn himself is actually not lying on a physiological level: he is faithfully reporting the contents of his mind. When the head detective asks him: what did you do last night? Shawn conjures up the image of a Nintendo he found while rummaging through the house and innocently reports that he played video games. Here we find a practical application of the distinction between the affect, reflected by a physiological response, and the intellect, which finds its expression through a verbal report.

Here is another example. I watched a video recently where an actor mixed together mayonnaise, mustard, coffee, and so on into a blender. In the next scene, we see him drinking a concoction of the same color. My immediate reaction was to be disgusted, since the camera work made it seem like it was a natural transition and he was faithfully drinking what was created in the previous scene. But I could immediately turn my disgust into appeal by thinking about what the drink actually was: probably some mix of chocolate milk and raspberry syrup by the looks of it. The flickering between those two affects was facilitated by my conscious semantic processing of the visual image — from disgusting mix, to sweet drink, back to disgusting.

Damasio combines both hard neuroscience and findings from clinical neurology in order to mount his critique of Descartes’ res cogitans. His book is a must-read for anyone who wishes to investigate the emerging philosophical implications of the brain sciences.

In part II, we’ll examine how another neuroscientist, Daniel Dennett, responds to Descartes’ philosophical assumptions by picking apart some findings from cognitive psychology.