Regular articleIncreased activation in the right insula during risk-taking decision making is related to harm avoidance and neuroticism
Introduction
Decision making, i.e., selecting an action from a set of alternatives with an uncertain outcome, consists of several component processes. A particularly important component of decision making is risk taking, which can be defined as the propensity to select an action with the potential for a relatively large beneficial or adverse outcome over an alternative action that results in a relatively small beneficial outcome Slovic, 1987, Mellers, et al., 1997. Risk taking itself, however, can be broken down into several components, including anticipation, reward, and punishment-related processing.
Abnormalities of risk-taking aspects of decision-making behavior have been observed in several psychiatric disorders Mogg et al., 1991, Rahman et al., 2001, American Psychiatric Association, 1994, Rahman et al., 1999, including substance-related syndromes (Rogers et al., 1999a). For example, substance dependent subjects are more likely to select a high gain/high-risk alternative (Bechara, 2001) over a low-gain/low-risk alternative even when the former alternative is associated with a disadvantageous long-term outcome.
Experimentally, risk-taking decision-making behavior appears to be highly sensitive to context. For example, the selection of the risky alternative is dependent on the number of other available outcomes (Weber et al., 1992), on the stimulus context (Mellers and Chang, 1994), and on cultural background of the subject (Hsee and Weber, 1999). One common approach to examine risk-taking behavior is to present subjects with a choice between a sure thing and a gamble (Yates and Stone, 1992). By varying the expected value of each action alternative (i.e., the magnitude of the beneficial effect multiplied by the likelihood of the outcome), one can determine whether subjects are risk seeking (selecting the gamble even when the expected value is lower than the sure thing) or risk averse (selecting the sure thing even when the expected value of the gamble is higher).
Functional neuroimaging studies have shown that risk-taking decision making is critically dependent on the activation of inferior prefrontal cortex Paulus et al., 2001, Ernst et al., 2002, ventromedial and ventrolateral frontal cortex Elliott et al., 1999, Elliott et al., 2000a, Rogers et al., 1999b, anterior cingulate (Elliott et al., 2000a), insula (Critchley et al., 2001), and parietal cortex (Paulus et al., 2001). The anterior cingulate has been implicated in the response selection process when the reward magnitude is altered (Bush et al., 2002), whereas the nucleus accumbens has been shown to activate during anticipation of reward (Knutson et al., 2001). Others have argued that anterior cingulate activation during decision making is related to the degree to which the outcome is uncertain (Elliott and Dolan, 1998), whereas the activation in the nucleus accumbens is due to the calculation of an error signal between an expected and received reward (Pagnoni et al., 2002).
The precise role of the neural substrate underlying risk-taking decision making is not fully understood. The somatic marker hypothesis (Damasio, 1996) has provided a conceptual basis for processes involved in risk-taking decision making and has been used to link discrete neural substrates to risk-related behaviors. This hypothesis poses that external or internal stimuli initiate a state that is associated with pleasurable or aversive somatic markers. These markers function to guide the person's behavior by biasing the selection toward actions that result in an increase in pleasurable somatic markers (while avoiding actions resulting in aversive somatic markers).
The neural systems underlying the somatic marker hypothesis comprise the ventromedial and orbitofrontal cortex, amygdala, insula, and ventral striatum. In particular, the insula acts as a critical interface between affective inputs from limbic structures such as the orbitofrontal cortex, amygdala (McDonald et al., 1999), and anterior cingulate and the attentional prefrontal-parietal network in the processing of somatic states associated with risk-taking decision making (Bechara, 2001). Within the context of the somatic marker hypothesis, the insula has been conceptualized as part of both the “body” and the “as-if” loop system that is critical for the initial representation and the reenactment of somatic markers (Bechara, 2001). In this scenario, increased activation in the insula may signal the strength of the somatic state. If the insula signal is associated with aversive somatic markers, a relatively large activation during a decision-making situation would signal a potentially aversive outcome and may guide the subject to avoid the selection of a risky action alternative.
This investigation examined the hypothesis that the degree of risk-taking is related to the degree of activation in the insula. Specifically, it was hypothesized that a large activation in the insula during a risky response, which would correspond to a potent aversive representation of a somatic state, is associated with a lower propensity to select a risky response. Moreover, if insula activity were related to risk-taking behavior and not to response to punishment, one would expect to observe differential activation during risk-taking trials that were not punished versus those that were punished. Finally, to examine the external validity of this approach, two temperament or personality measures were obtained and correlated with activation in the insula. Cloninger (1987) developed the Temperament and Character Inventory (TCI) to quantify several dimensions of personality. These temperamental dispositions are defined in terms of the basic stimulus–response characteristics and comprise novelty seeking, harm avoidance, and reward dependence. In particular, harm avoidance has been used as a measure of anxiety proneness and reduced risk-taking propensity (Cloninger et al., 1998). In addition, the NEO personality inventory (Costa and McCrae, 1992), a measure of five personality factors, was used to obtain convergent validity that temperamental sensitivity to negative stimuli is closely associated with harm avoidance. In combination, it was hypothesized that a high degree of harm avoidance (i.e., the opposite of risk taking) or neuroticism is associated with a large activation in the insula during a risky response.
Section snippets
Subjects
Seventeen healthy, right-handed subjects (6 females and 11 males) age 38.3 years ± 1.4 (range 27–53) with an average education level of 14.7 ± .5 years (range 11–18) without a life-time history of Axis I DSM-IV disorders based on a structured clinical interview for DSM-IV diagnosis (Spitzer et al., 1992) participated in this study, which was approved by the UCSD Human Research Protection Program. These subjects gave their informed, written consent and performed a Risky-Gains decision-making
Behavioral results
Subjects selected the “safe” 20 response 46% ± 4 of the time, the “risky” 40 response 26% ± 5 of the time, the “risky” 80 response 23% ± 5 of the time [F(2, 32) = 4.75, P < 0.05] and failed to respond 4% of the time. Therefore, subjects selected “safe” and “risky” responses with similar frequencies. As shown in Fig. 2, there was a significant interaction between prior punishment and response type [F(2, 32) = 9.0, P < 0.01] wherein subjects made fewer 40 and 80 (risky) responses after punishment.
Discussion
This investigation yielded three main findings. First, right anterior insula (BA 13) activation was significantly larger when subjects selected a “risky” response versus selecting a “safe” response but also showed significant activation during punishment. Moreover, bilateral insula and left superior parietal lobule activation was larger during nonpunished “risky” responses than during punished trials. Second, in both cases the degree of insula activation was related to the probability of
Acknowledgements
We acknowledge the invaluable help of Larry Frank, Rick Buxton, and Eric Wong in supporting the fMRI experiments. This work was supported by grants from NIMH (R21DA13186, M.P.P.), NARSAD (M.P.P.), and support from the Veterans Administration via Merit Awards (M.P.P. and M.B.S.) and a VISN 22 MIRECC.
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