Does autonomic arousal distinguish good and bad decision-making ? Healthy individuals ’ skin conductance and heart rate reactivity during the Iowa Gambling Task

The Somatic Marker Hypothesis (SMH) proposes that physiological feedback to the brain influences cognitive appraisal and decision-making; however, the strength of evidence in support of the SMH is equivocal. In this study we examined the validity of the SMH by measuring physiological arousal in a population of healthy individuals playing the Iowa Gambling Task (IGT); a computerised card game designed to assess real-life decisionmaking. We also aimed to clarify uncertainty regarding the influence of reinforcer type and impulsiveness to IGT performance and the SMH. Skin conductance level (SCL) and heart rate reactivity were measured in forty-one participants performing the IGT using either facsimile or real money. Participants were categorised as non-impaired or impaired on the basis of their IGT performance, and any differences in performance and physiological between groups were examined. Heart rate data did not reveal any effects. Robust differences in SCL reactivity during the task were not found between impaired and nonimpaired individuals; however, marginal SCL rises were observed when non-impaired individuals anticipated and received a reward from disadvantageous choices compared with advantageous ones. This effect was found only when using facsimile money and did not occur in impaired individuals, suggesting some effect of reinforcer type on physiological activity and performance, and a difference in the physiology of impaired and non-impaired individuals. No significant differences in impulsiveness were found between impaired and non-impaired individuals. The findings suggest that autonomic activity is independent of long-term good or bad decision-making, and may reflect differences between decks in the magnitude of gain and loss. It is concluded that further substantiating evidence is needed for the SMH to continue as an explanation for human decision-making. Autonomic arousal during good and bad decisions 3 Does autonomic arousal distinguish good and bad decision-making? Healthy individuals’ skin conductance and heart rate reactivity during the Iowa Gambling Task Since its introduction less than 15 years ago, the Somatic Marker Hypothesis (SMH) (Damasio, 1994; Bechara, Damasio, Damasio, & Anderson, 1994) has quickly become an influential account of human decision-making. The central proposal of the SMH is that physiological states of the body (somatic state) act to guide decisions. When a decision must be made, factual information regarding the possible response options and their likely outcomes is recalled; associated with each response option outcome is a somatic state, which represents the physiological response of the body to the given situation. When considering which response option to pursue, somatic states mark the ‘goodness’ or ‘badness’ of each outcome based on the consequences of previous encounters with the same or similar situations. These somatic markers thereby assist decision-making by rapidly rejecting bad choices and endorsing good ones, making the accompanying logic-based, cost-benefit analysis more manageable. This process often operates outside of conscious awareness, as somatic markers can act both overtly and covertly. Fortunately, indicators of autonomic nervous system activity, i.e. skin conductance level (SCL) and heart rate, may be used to signal somatic marker activity. Accordingly, the SMH predicts changes in SCL and heart rate when possible response options are being considered and somatic markers are acting to guide this process, i.e. in the period when a decision is being anticipated. The Iowa Gambling Task (IGT) (Bechara et al., 1994) was created by Bechara and colleagues to provide an experimental measure of human decision-making and the SMH. The task was designed to mimic real life decision-making in the way reward, punishment and uncertainty are represented. Playing the task involves selecting sequential cards from four decks (A, B, C and D) in order to win money. The decks differ in the magnitude and frequency of money lost and won. Decks A and B are considered bad and indicative of Autonomic arousal during good and bad decisions 4 disadvantageous decision-making in that frequently selecting from these decks leads to longterm losses. Conversely, decks C and D are considered good or representative of advantageous decision-making as frequently selecting from these decks leads to long-term gains. Normal performance on the task is characterised by selecting more cards from the good decks than the bad ones. Bechara et al. (2001) reported that healthy individuals playing the task develop a preference for the good decks (C and D), and generate anticipatory skin conductance response (SCR) prior to a selection from a bad deck (A or B). Carter and Pasqualini (2004) support the role of anticipatory somatic activity in guiding decisions in healthy individuals, reporting a positive correlation between anticipatory autonomic response and successful performance on the gambling task. Crone, Somsen, Van Beek, and Van Der Molen (2004) also found changes in SCL and heart rate activity preceded the risky choices of healthy individuals showing good, but not poor, performance. Does Physiological Reactivity Guide Decisions? Although the SMH emphasises the role of anticipatory somatic markers as chief in guiding future decisions, the development of anticipatory somatic markers is contingent on appraisal (i.e. outcome) physiology. Individuals acquire somatic markers via prior experience using feedback from appraisal physiology. Accordingly, individuals who show poor or absent appraisal physiology should be unable to develop anticipatory somatic markers to guide future decisions, and thus exhibit impaired decision-making. Consistent with this, Suzuki, Hirota, Takasawa and Shigemase (2003) found, in a population of 40 healthy individuals, that low appraisal SCRs in response to early trials were related to persistence in selecting risky choices on later trials. However, despite the existence of greater magnitude anticipatory SCRs in response to risky choices, the expected relationship between anticipatory SCRs and performance was not supported, nor was there evidence of anticipatory SCR development over time. These findings appear contrary to the assumption that decision-making performance depends on the development of anticipatory SCRs, and suggests that appraisal Autonomic arousal during good and bad decisions 5 physiology underlie individual differences in decision-making. Conversely, Crone et al. (2004) found autonomic activity during appraisal to be independent from performance strategy, while heart rate slowing and SCL were greater preceding selections from bad but not good decks. Tomb, Hauser, Deldin and Caramazza (2002) further challenge the notion that somatic states act to mark the long-term consequences of decisions. They propose that high magnitude physiological responses are elicited when healthy participants anticipate bad decks, because bad decks yield rewards and punishments of high magnitude compared to good decks. As such, the larger anticipatory SCRs observed for bad decks represents the magnitude of wins and losses rather than long-term outcomes. Tomb et al. (2002) provide support for this idea using a modified version of the gambling task, in which good decks were associated with a higher magnitude of reward and punishment than bad decks. They concluded that card selections are driven by long-term consequences, whereas anticipatory SCRs reflect the immediate choices at hand. Further criticisms of the SMH are presented by Maia and McClelland (2004) who conclude that there is no reason to think that somatic markers, as indexed by SCRs, play a causal role in guiding decision-making. They base their conclusion on findings that healthy participants demonstrate sufficient conscious knowledge regarding the gambling task to behave advantageously. Real versus Facsimile Money The IGT has been subject to several variations in administration, one example of which is alteration in the type of reinforcer used to perform the task (e.g. real versus facsimile). Research indicates good reason to believe that provision of a financial incentive influences performance on decision-making tasks (Hertwig & Ortmann, 2001). With this in mind, it is non-trivial that the original gambling task involves players using facsimile or play Autonomic arousal during good and bad decisions 6 money, whereas other researchers have altered this to using real money (e.g. Schmitt, Brinkley, & Newman, 1999; Bowman & Turnbull, 2003; Suzuki et al. 2003). Bowman and Turnbull (2003) compared the effect of using real versus facsimile money during the gambling task. No significant differences were found as a consequence of money type; however, a non-significant variation between the two healthy groups’ performance indicated steep avoidance of bad decks following substantial losses in the real money condition. Bowman and Turnbull (2003) suggest that this (non-significant) difference may indicate somatic markers of enhanced magnitude when using real money; however, their study did not incorporate physiological evidence to substantiate this claim. A subsequent study by Carter and Pasqualini (2004) explored Bowman and Turnbull’s (2003) suggestion in a group of 30 healthy women, finding anticipatory SCR was related to amount of money won or lost, and indicating that stronger autonomic responses accompany better performance. However, contrary to Bowman and Turnbull’s (2003) prediction, there was no difference in aSCR magnitude of real versus facsimile money conditions. Financial incentive is suggested as the primary explanation for any effect of real versus facsimile money, and accordingly studies comparing these reinforcer types have allowed participants to keep all or a proportion of the final winnings (Schmitt et al., 1999; Bowman & Turnbull, 2003; Carter & Pasqualini, 2004; Fernie & Tunney, 2006). However, the mechanism