Somatic Marker Hypothesis

Critically evaluate to what extent the ‘somatic-marker hypothesis’ explains how decisions are made in the face of an uncertain outcome. In mind of Kim Sterelny’s (2007) statement that ‘Human Life is one long decision tree’, it is not surprising that there has been a vast amount of research into the process of how we evaluate the desirability of alternative choices and select a particular option.
One area of research, of particular interest here, is Damasio’s Somatic Marker Hypothesis (SMH) (1991) which uses the neuroeconomic approach through its integration of the fields of psychology, neuroscience and economics to invoke an understanding of how one makes a decision (Damasio, Tranel & Damasio, 1998). This Theory supports the RAF hypothesis that significant risky outcomes elicit emotional reactions (Stanfey, Loewenstein, McClue & Cohen, 2006,).
The SMH proposes that stochastic decision making is the result of emotion-based biasing signals in the body- in particular from the Ventromedial Prefrontal Cortex (VMPFC) (Bechara, Damasio, Tranel & Damasio, 2005). This concept will be discussed in further detail (with reference to it’s origin and experimental support), followed by a critical analysis of the extent to which the SMH successfully explains what it contends to.

Since the SMH focuses solely on the role of emotion in decision making, the Rationale Planning Model (1995) will also be examined in comparison to the SMH for it’s explanation of decision making as a purely logical and rational process. The Rational Planning Model by Banfield (1995) proposes that the decision maker consciously undergoes five steps when coming to a decision and so approaches the choice in a very rational manner. Subsequently, an evaluation of the two theories for stochastic decision making will follow to discern how well they account for stochastic decision making.
The SMH stemmed from attempts to explain why a patient (E. V. R. ), with an ablation of the VMPFC, often engaged in behaviors that were detrimental to his wellbeing (Damasio, 1996). Emotion was originally believed to be a disruptive force in decision making, but since the VMPFC is in charge of emotional function, it was now speculated to be essential for the ability to make a decision. Further investigation into this phenomenon through neuropsychological examination, found that those patients with damage to their VMPFC evinced a generally flat affect and an inability to respond to emotional situations (Bolla et al. 003). Thus, Damasio extracted that the decision making deficits experienced by these patients was a result of this altered psychophysiological response (Damasio, 1996). His SMH contends that when presented with a decision, the normal brain will use the VMPFC to react emotionally to the situation and generate ‘somatic markers’ in order to come to a decision. A somatic marker is best defined as the brains construction of a physiological change that it apprehends for the selection of a particular strategy. It supposedly guides attention towards the more advantageous option (Dalgleish, 2004).
This enables the organism to react quicker to external stimuli as it no longer needs to wait for the activity to emerge in the periphery before it can elicit a reaction (Dalgleish, 2004). Furthermore, the VMPFC is thought to support association learning between complex situations and the somatic changes usually experienced during a particular situation (Jameson, Hinson, & Whitney, 2004). Put simply, once a previous situation that elicited similar somatic markers is identified, the VMPFC can use past experiences to rapidly evaluate possible behavior responses.
So when the VMPFC suffers impairment, the somatic marker system can no longer be activated, resulting in an absence of physiological feedback and an inability to predict long term punishments and rewards. This occurrence has been termed ‘Myopia for the future’, where a decision may only be formulated by the use of a logical cost-benefit analysis (Dalgleish, 2004). However, if one was presented with an uncertain situation, the result would be marked impairment. The SMH substantiates its argument through the experimental paradigm: the Iowa Gambling Task (IGT) (Bechara et al, 1997, cited in Dunn, Dalgleish & Lawrence, 2006).
The task measures decision making in patients with VMPFC brain lesions and compares it to those people with a normally functioning VMPFC. The experiment involves selecting a card from a choice of four decks- each of which attributes different levels of reward and punishment in the form of winning or losing pretend money. Two of the decks provide a low reward and a low level of punishment and were labeled the advantageous decks. The remaining two decks provide a high reward and a high level of punishment and were named the disadvantageous decks. Control articipants initially sampled both decks equally but shifted their choice to the advantageous decks after experiencing the high punishment from the disadvantageous one. Conversely, the subjects with damage to their VMPFC were seemingly insensitive to the negative consequences of the disadvantageous decks and would continually choose from these decks on account of their high reward (Dunn et al. 2006). The study concludes that the reason the patients failed to comprehend the advantageous decks as the more profitable option, was due to their inability to generate the somatic markers necessary for such a realization (Dunn et al. 006). Furthermore, Bechara et al. (2005) combined the gambling task with the measurement of skin-conductance response (SCR). It was found that control subjects elicited larger anticipatory SCRs before picking from the disadvantageous decks as oppose to the advantageous decks. The absence of anticipatory SCRs in the VMPFC lesion group confirmed the failure for the VMPFC to activate negative, physiological marking signals based on previous punishment history which ultimately made them insensitive to the possibility of future punishment from the deck (Schmitt, Brinkley & Newman, 1999).
Hence, a positive correlation between successful IGT performance and a healthy participants’ ability to develop somatic marker signals was reported. The extensive validation of the IGT, strengthens the evidence for the role of emotion in decision making. For example, patients with various kinds of frontal lobe damage and patients with lesions to the lateral temporal or occipital cortex have also been tested in the IGT (Best, Williams & Coccaro, 2002). Of these patients, only the ones with damage to their VMPFC appear to be impaired on the task (Bechara, Damasio & Damasio, 2000).
Furthermore, Overman (2004) has conducted a study outside of the Iowa laboratory and has replicated Damasio’s findings with the extension of gender differences. Overman’s results showed that adolescent men chose from the decks on the basis of long-term outcome only. Moreover, the predictive validity of the IGT and therefore SMH, has demonstrated an association between the response of OCD patients to pharmacotherapy and performance on the IGT (Cavedini, Bassi, Zozi & Bellodi, 2004).
This depicts the behavioral form of the IGT to be a very sensitive measure of decision making as its results are highly applicable to real world decision making (e. g. those with OCD). Although the study does much to support the SMH argument, it has also received a lot of criticism which will be subsequently addressed. It has been contested that the work from the Iowa laboratory provides only superficial support for the SMH, since closer analysis can reveal issues that potentially undermine its argument for decision making in the face of an uncertain outcome.
For example, Maia & McClelland (2004) contend that the IGT can be performed through access to conscious, explicit knowledge since the task allows a lengthy time to deliberate over each decision- especially since the outcomes are presented in explicit numerical form. Thus, they refute the claim that task acquisition necessarily requires the generation of non conscious ‘somatic marker’ signals which effectively weakens the extent to which the SMH accurately explains decision making in terms of emotion- for it may not be the result of an implicit neural mechanism (Maia & McClelland, 2004. Another criticism of the IGT (and therefore the SMH) is that the patients with VMPFC damage could have been quite apathetic to the study’s demands and expectations. Barrash, Tranel & Anderson (2000) report that patients with lesions to their VMPFC often experience symptoms of apathy and are actually capable of improving their emotional response to affective images if instructed to look carefully. Therefore, if the patients are in fact competent of generating anticipatory SCRs and successfully completing the task, it can be postulated that enhancing their engagement levels would raise their results to match the control groups.
In terms of the implications this would have for the SMH, it would serve as evidence that emotion does not play that great a role in decision making since they can still obtain the same results with impaired emotional ability. Furthermore, Fellows and Farah (2005) have suggested that the syndrome of apathy may deserve more attention in understanding impaired decision making. Similarly, another symptom of VMPFC damage, which can adversely affect performance in the IGT, is impaired reversal learning (Rolls, Hornak, Wade & McGrath, 1994).
The IGT is centred on a response reversal in which involves a shift in preference from the two initially rewarding decks to the other two decks due to subsequent punishment (Rolls et al. 1994). Both Fellows & Farah (2005) and Rolls et al (1994), corroborate that lesions to the VMPFC allow normal acquisition but impaired reversal on simple reversal learning tasks. Therefore, the impaired reversal learning, rather than the inability to generate somatic markers, may well account for why patients find it so difficult to perform correctly in the IGT.
Fellows & Farah (2005) devised a study to test this notion by removing the response reversal. It was found that by eliminating the rewards of the two disadvantageous decks in the opening trials, the performance of the VMPFC impaired patients was the same as that of the control volunteers. This research suggests that the IGT may not have been testing the role of emotion in decision making but instead, how capable the subjects were in their response reversal.
Therefore, the extent to which the SMH explains how decisions are made is further limited since the evidence that emotions play a direct role is very weak. Additionally, the SMH is arguably only applicable to certain decision making and cannot account for those decisions that need rationality and a thoughtful, conscious planning process. Banfield’s Rational Planning Model (1959) (RPM), on the other hand, may serve as a good explanation for decision making in such a situation.
Banfield states that a rational decision is made when the decision maker lists all the opportunities for action, recognises all the consequences and selects the action based on the preferred consequence. Additionally, Banfield defines a ‘plan’ as a decision with regard to a course of action, involving a similar process as any rational choice. The RPM consists of four main stages: the analysis of the situation, the end reduction and elaboration (formulating an image of the future had an option been picked), the design of courses of action, and the comparative evaluation of consequences (Banfield, 1995).
Banfield’s RPM is the most widely subscribed planning theory to date and although it has experienced criticism, it has been hailed very useful in explaining how we make important decisions. According to Stiftel (2000), important decisions are ones which demand explicit conscious planning such as buying a house or taking a new job. These decisions are arguably unlikely to be a result of the emotional hunches or gut instincts that Damasio discusses since they almost always involved a mental list of pros and cons before arriving at a decision.
However, this theory fails to explain why some people make irrational and illogical decisions in the face of an uncertain outcome. For example, criminals do not logically plan or weigh up the consequences of an action before undertaking, which highlights that there are multiple explanations for how people make decisions. Banfield recognises that people are generally very opportunistic in their daily decision making as rather than materialising a course of action, people will improvise and meet each crisis as it arises.
For instance, large industries rarely look forward more than five to ten years and government planning is even less effective (Stiftel). Since Banfield himself appreciates that the majority of decisions are the unintended outcome of a ‘social process rather than the conscious product of deliberation and calculation’, there is clearly a cause to investigate the role of social processes in decision making (Banfield, 1995 pp. 13). In conclusion, the extent to which the Somatic Marker Hypothesis explains decision making in the face of an uncertain outcome is limited.
As it has been demonstrated, Damasio’s SMH attempts to pin decision making down to emotional biasing signals alone and has received various criticisms for its empirical support. For example, it attempts to validate its theory by testing VMPFC patients who may already be too cognitively impaired to perform the task (Barrash et al, 2000). Additionally, the extent to which the IGT measures an implicit response has also been questioned on the grounds that the task allows a great deal of time for deliberation (Maia & McClelland).
Thus, Banfield’s Rational Planning Model was examined as an alternative explanation for decision making. The RPM does a lot to discredit the SMH and is essentially a valuable explanation of how we make decisions since it highlights that the majority of important decisions force the individual into a conscious process of planning and analysing. However, like the SMH, the RPM alone cannot explain decision making for there are individuals (criminals) who defy deliberation. This highlights that decisions are most likely the cause of an interplay of factors, depending on both the situation and person.
To summarise, the SMH does little to explain the tricky phenomenon of decision making in the face of an uncertain outcome- but it would be too deterministic to deem this process down to just one theory alone. Referencing: Banfield, E. C. (1959), “Ends and means in planning”, International Social Science Journal, Vol. 11, pp. 361-8. Barrash, J. , Tranel, D. , Anderson, S. W. , (2000). Acquired personality distrubances associated with bilateral damage to the ventromedial prefrontal region. Developmental Neuropsychology 18 (3), 355–381. Bechara, A. , Damasio, H. , Damasio, A. R. , (2000).
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Damasio, A. R. , 1996. The somatic marker hypothesis and the possible functions of the prefrontal cortex. Philosophical Transactions of the Royal Society of London (series B) 351 (1346), 1413–1420. Damasio, A. R. , Tranel, D. , Damasio, H. C. (1998) Somatic markers and the guidance of behaviour. In Jekins, M. J. , Oatley, K & Stein, L. M. (Eds. ), Human Emotion: a reader (pp 122- 125). Oxford: Blackwell. Dunn, D. B. , Dalgleish, T. , Lawrence, A. D. (2006). The Somatic Marker Hypothesis: A critical evaluation. Neuroscience and Biobehavioral Reviews. 30. , 239–271. Fellows, L. K. , Farah, M. J. 2005a. Different underlying impairments in decision-making following ventromedial and dorsolateral frontal lobe damage in humans. Cerebral Cortex 15 (1), 58–63. Jameson, T. L. , Hinson, J. M. , & Whitney, P. (2004). Components of working memory and somatic markers in decision making. Psychological Bulletin & Review, 11, 515–520 Maia, T. V. , McClelland, J. L. , 2004. A reexamination of the evidence for the somatic marker hypothesis: what participants really know in the Iowa gambling task. Proceedings of the National Academy for Science USA 101 (45), 16075–16080. Overman, W. H. , 2004.
Sex differences in early childhood, adolescence, and adulthood on cognitive tasks that rely on orbital prefrontal cortex. Brain and Cognition 55 (1), 134–147. Rolls, E. T. , Hornak, J. , Wade, D. , McGrath, J. , 1994. Emotion-related learning in patients with social and emotional changes associated with frontal lobe damage. Journal of Neurology Neurosurgery and Psychiatry 57 (12), 1518–1524. Schmitt, W. A. , Brinkley, A. C. , Newman, P. J. (1999). Testing Damasio’s Somatic Marker Hypothesis With Psychopathic Individuals: Risk takers or Risk Averse. Journal of Abnormal Psychology. 108 (3), 538-543.
Sanfey, A. G. , Loewenstein, G. , McClure, S. M. , & Cohen, J. D. (2006). Neuroeconomics: cross-currents in research on decision-making. Trends in Cognitive Science, 10, 108-116. Sterelny, K. (2007). Cognitive Load and Human Decision, or, Three Ways of Rolling the Rock Up Hill. In Carruthers, P. , Laurence, S. , & Stich, S. (Eds. ), The Innate Mind: Volume 2: Culture and Cognition (PP. 148-152). Oxford Scholarship Online. Stiftel, B (2000). “Plannin theory. II. The national AICP examination preparation course guidebook. Ed Roshi Pajaseyed. Am. Inst. Cert. Planners: Washington DC. Pp. 4-16

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