The role of the insula in many human behaviors
Following up on my lead on Antoine Bechara’s upcoming visit, it is worthnotinv one of the new trends in decision making research. In particular, working from an extension of the somatic market theory and the role of ventromedial prefrontal cortex (vmPfC), Bechara and colleagues have recently demonstrated how the role of the insula seems to play an important role in decision making involving risk and aversion.
In the article entitled Differential effects of insular and ventromedial prefrontal cortex lesions on risky decision-making, the researchers compared patients with lesions to vmPfC and the insula to healthy controls and lesion controls on the Cambridge Gamling Task (nice demo here). The authors note that:
The vmPFC and insular cortex patients showed selective and distinctive disruptions of betting behaviour. VmPFC damage was associated with increased betting regardless of the odds of winning, consistent with a role of vmPFC in biasing healthy individuals towards conservative options under risk. In contrast, patients with insular cortex lesions failed to adjust their bets by the odds of winning, consistent with a role of the insular cortex in signalling the probability of aversive outcomes. The insular group attained a lower point score on the task and experienced more ‘bankruptcies’.
The results thus confirmed previous findings of a role of the vmPfC in gambling tasks, while the surprising finding was that insular lesions would also have detrimental effects on decision making. in particular, while vmPfC patients responded to reduced likelihood ratios of the gambles, betting behaviour in insular patients did not show much response to decreasing probabilities. This is demonstrated nicely in the following figure:
The effect of ratio on betting behaviour in the four groups of participants: healthy controls, vmPFC lesions, insular cortex lesions and the lesion control group.
Furthermore, over the course of the entire gambling task, insular patients suffered significantly more bankrupcies than both the vmPfC group and control groups. This does suggest that one role of the insula is guiding behaviour through aversive coding. In other words, it may be that the insula is responsible for loss aversion (as well as risk aversion, judging from the task).
The researchers further suggest that the findings were expected from the somatic marker theory:
The detrimental effect of insular cortex damage on emotional decision-making is also predicted by the Somatic Marker hypothesis (Damasio, 1994; Bechara and Damasio, 2005), which posits a crucial role for the insular cortex in holding the representations of bodily states associated with different choice options.
The results are also relevant to other studies, including Lawrence et al. (2009), who report that using the Iowa Gambling Task, choices from disadvantageous versus advantageous card decks produced activation in the medial frontal gyrus, lateral orbitofrontal cortex, and insula. So does the insula play a role in other forms of decision making, and is it a cause in pathological gambling? To date, no conclusive studies have emerged, which is why our own research has now turned to aversion-related activations in gambling, and the study of the dynamics (and overlap) between aversion related and reward related neural functions. The recent study by Clark et al demonstrates that the insula is a structure – long ignored – to take into considerations in decision making studies.