Supplementary Figure 9: Affective involvement of message and choice conditions.

The fact that we did not observe an effect of OFC damage on behavior in the present investigation is perhaps surprising given existing data on the role of OFC in prosocial behavior. One possible explanation for the OFC results in the present study is that our games lacked a strong affective component, including the need to regulate emotional responses to self-generated or external stimuli that is often attributed to OFC functioning. In particular, Koenigs et al.¹⁶ found that OFC patient decisions deviated from those of healthy participants only in moral dilemmas involving a high degree of conflict between emotional responses and utilitarian goals. To investigate this possibility, we ran an additional study in which healthy participants (n=51) recruited online from Amazon’s Mechanical Turk made a series of comparisons between the degree of affective involvement in our task versus the moral dilemmas borrowed from Koenigs et al.¹⁶. Subjects were randomly assigned to rate the emotional intensity of a trial from our Choice condition or Message condition in comparison with one of each from the following types of moral dilemmas as classified according to Koenigs et al.: (i) high-conflict between emotion and utilitarian concerns, (ii) low-conflict between emotion and utilitarian concerns, and (iii) impersonal cases, which are associated with lower emotional involvement. To the extent that low affective involvement helps to explain the lack of difference between the OFC and healthy comparison cohorts observed in our study, it should be the case that individuals experience substantially less emotional involvement in our task than in both High- and Low- Conflict dilemmas, and that this involvement should be comparable to, or lower than, the Impersonal dilemmas. Consistent with this possibility, we found that participants rated both the Choice and Message conditions of our task as being significantly lower in emotional intensity than all three types of moral dilemmas used in Koenigs et al. (one-sample t-test p <.0001 for all comparisons, two-tailed). Similarly, past explanations of OFC patients’ lower giving rates in the standard Dictator Game have centered on the role of OFC in guilt aversion. The current design minimizes guilt by instructing the participant that the recipient will never know the original payoff amounts (Online Methods), which perhaps accounts for the lack of effect of OFC damage. This view is consistent with previous observations that DLPFC is involved generally in cognitive control of impulses, be they emotionally-derived or not. However, our hypothesis is necessarily speculative given the lack of direct manipulation of emotional intensity in the current task. Indeed, other studies have suggested that OFC patients exhibit increased, rather than decreased, emotional reactivity to direct personal frustration or provocation¹⁶. Future studies combining economic games with emotional manipulations are thus needed to clarify these questions. An additional possibility is that behavioral differences instead reflect differences in lesion cohort characteristics, such as age or etiology (Online Methods Table 1). For example, it is possible that, due to the TBI nature of damage in our OFC cohort, OFC damage actually had the effect of shifting patient behavior from a premorbid abnormal state into the normal range. Future experiments with larger cohorts varying in in etiology will be needed to test these hypotheses.