Expectancy of Pain and Disgust on moral decision

Since it was first theorized that moral intuitions develop from the embodied experience of emotions at time of moral judgment⁵⁴³, studies have demonstrated how induction of emotions could bias decisions of morality^630,631. Indeed, recent theories propose that disgust is an embodied emotion of moral judgment270,468,480,632,633. This idea stems from accumulated evidence linking physical to moral disgust showing: modulation of physical disgust on moral disgust479,540,556,632, positive correlation between the sensitivity to physical and to moral disgust^634–636, and shared facial expressions⁴⁷⁵. For instance, participants evaluated moral transgressions as more morally wrong after sitting at a dirty desk⁴⁶⁸, smelling a disgusting odor⁴⁶⁸, or tasting a bitter beverage^479,475. Critically, however, all previous data fail to distinguish between two plausible hypotheses in which disgust can modulate moral judgments. One possibility is that, as a negative and salient event, disgust can alert us to the moral salience of a situation. In this scenario, disgust is not unique to morality, and therefore other aversive events, such as pain, can result in similar shifting of attention resulting in harsher moral judgments.

Alternatively, disgust might trigger a genuine conceptual shift from merely conventional to moral coding. Therefore, in this case, only disgust should bias the moral judgments, but not pain.

Experiment 3 and 4 were designed to test whether moral judgments could be modulated in a comparable or differential way by pain and disgust expectancy. Indeed, as shown in Experiments 1-2, cues predictive of pain or disgust trigger a representation of the upcoming event which sensory-specific information is retained, and which affects the behavioral/neural responses of a subsequent event of the same modality. Consequently, the logic underlying Experiments 3-4 is to see how these same cues affected moral cognition, in order to ascertain whether the representation of others’

inappropriate behavior is itself modality-specific. Furthermore, our experimental design also allowed to test putative bidirectional effects, in which the inappropriate behavior described in the dilemma biases participants’ reactions to disgusting odors or to painful temperatures. Although theoretically relevant and, at least to our knowledge, unprecedented, this paradigm revealed the following methodological challenges.

Numerous studies testing moral cognition often compared dilemmas describing inappropriate behavior with dilemmas describing ordinary actions, as a dichotomic factor “moral vs. non-moral”.

Although moral and non-moral dilemmas are usually preselected to diverge as categories across several dimensions (see SI Figure 32), a considerable variability exists within each category (e.g., killing someone to save other five might be considered slightly more acceptable than killing someone to gain money). Such variability is particularly problematic in paradigms such as ours, in which the dilemmas

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are randomly assigned to different expectation conditions, as it opens the possibility that putative expectation differences might be biased by idiosyncratic properties of the dilemmas. In our study we minimized this possibility by preselecting dilemmas with the least variability, and changing the assignment between the dilemmas and the expectancy conditions across subjects. Most importantly, we analyzed the data replacing the dichotomic factor “moral vs. non-moral” (used in previous studies), with the median appropriateness ratings associated with each dilemma as measured in a pilot study.

We believe this rating to be a good measure of the moral content of each dilemma (unbiased by the expectancy conditions) which does not describe the difference between moral and non-moral dilemmas, but takes into account also the subtle different within each group. By using this variable, we insured that any differential effect of the expectancy conditions on moral judgment should be estimated over and beyond any possible idiosyncratic confounds of the dilemmas.

4.3.2 Disgust expectancy biases moral processing

Our behavioral data clearly showed a modulation of disgust expectation on moral judgments that prevailed in both experiments. In particular, HD cues led to harsher judgments than LD cues, an effect which was found only under 1-tailed statistics (in the same direction of previous studies479,540,475,556) but replicated across Experiments 3 and 4. Most importantly, in both experiments as well HD cues led to harsher judgments than HP cues, suggesting that expectancy of disgust might influence moral judgments on top of putative effects played by amodal dimensions such as unpleasantness. An effect of unpleasantness is suggested only in Experiment 3, in which HP cues led to harsher effects than LP cues, but was not replicated in Experiment 4. Anyway, even accepting that amodal emotional dimensions might play a role on moral judgments, these do not explain the whole extent of our results, as in Experiment 3 olfactory cues (both LD and HD) lead to harsher judgments than equally-unpleasant thermal cues (LP and HP).

These behavioral observations are complemented with results from the analysis of the brain responses, which shows how that part of the neural network sensitive to the moral content of the dilemma was modulated by HD expectancy. Indeed, previous studies investigating the neural correlates of moral cognition converge in identifying a distributed network – called, “moral brain” – which includes dorsal (DMPFC) and ventral (VMPFC) portions of the medial prefrontal cortex, the precuneus (PC), the posterior cingulate cortex (PCC), the temporoparietal-junction (TPJ) etc. (see^531–

533,452 for meta-analyses). These regions were observed also in the present study, when testing for modulation of appropriateness on both the epochs in which participants read the dilemma and those in which they assessed its’ associated behavior. Most interestingly, within this network, the activity of PC/PCC in rating epochs was modulated by the inappropriateness of the dilemma prevalently when

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expecting HD (as opposed to LD or HP). Likewise, when focusing on the reading epochs, it was the posterior portion of the middle cingulate cortex (pMCC – about 40 mm more anterior to PC/PCC local maxima) who showed a stronger inappropriateness modulation when expecting HD. Overall, these data extend previous studies, not only highlighting the role played by physical disgust on moral processing, but also identifying which portion of the moral network mediates this role.

Indeed, although scholars agree that all the regions constituting the moral network might underlie a wide range of cognitive and affective processes, the role played by each region in moral processing is far from being understood. In their seminal study Greene et. al. (2001)⁴⁴⁶ proposed a subdivision between DMPFC/VMPFC, PC/PCC and angular gyrus (just above TPJ), implicated in dilemma with high emotional salience, and superior parietal and lateral prefrontal regions, implicated in dilemmas with low emotional salience and associated with more utilitarian responses. This segregation was proposed within a theoretical framework according to which individual decisions (including moral judgments) result from the interaction of at least two different brain systems (Dual-System model – see⁶³⁷ for an overview): the cognitive/deliberate system (slow, controlled, cognitively-demanding) and the affective system (fast, automatic, cognitively non-demanding). However, accounts such as the Dual-System Model have been criticized for their dichotomous separation between cognition and emotion, which appears over simplistic and not supported by empirical evidence464,448,638. More recently, Bzdok et al. 2012 used quantitative ALE meta-analysis to investigate the neural structures underlying moral cognition, and to which extent they were shared with networks implicated in other kinds of social processes⁵³². They found that TPJ and part of DMPFC were implicated in both moral cognition and mentalizing, hinting that the same neural structures involved in ascertaining others’

thoughts/beliefs/intentions are also recruited when evaluating others’ conducts (see also⁶³⁹). On the other hand, a different portion of DMPFC (~ 10 mm more ventral than that implicated in metalizing) was found to be recruited in both moral judgment and empathy tasks, thus suggesting also a role of those structures involved in the inference of others’ emotion. No overlap was instead found for PC and PCC, thus leaving open the question about the functional role of these regions.

To our knowledge, our data provide an unparalleled insight about the functional role played by PC/PCC in moral coding. Rather than processing information about others’ people intentions (as in mentalizing) or affective states (as in empathy), which are critical intrinsic properties of any scenario/dilemma in which conducts are evaluated, PC/PCC might instead underlie the role played by participants’ own affective (disgusting) response. In light of this, previous studies repeatedly associated the activity of PC/PCC with emotion imagery⁶⁴⁰, memory for coherent social narratives⁶⁴¹, self-processing (together with the medial prefrontal regions see^642,643 for meta-analytical evidence)

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and autobiographic memory⁶⁴³. Our study extends previous findings, suggesting how PC/PCC might bridge a representation of one’s own emotional (disgusting) states with that of others’ inappropriate behavior. In this perspective, whereas witnessing (reading) an inappropriate behavior might trigger modality-specific representation of physical disgust in the middle cingulate cortex (although the pMCC cluster from Experiment 4 is ~30 mm posterior to the MCC cluster from Experiment 2), PC/PCC might be involved in projecting such somatic representation into a more abstract domain, to address problems of high social relevance.

4.3.3 Inappropriate behavior biases disgusting experience

Within embodied accounts, scholars distinguish between simulation and metaphoric approaches, the first suggesting that conceptual processing recruits the exact same representations underlying sensorimotor experiences, whereas the latter suggests that conceptual processing recruits an abstract representation which is the projection of one’s sensorimotor experiences⁵⁴⁸. Within this framework, simulation effects are expected to be bidirectional: e.g., if the same representation underlies both physical disgust and moral processing, then physical disgust should bias moral processing, but also inappropriate behavior should bias disgust experiences. Instead, metaphoric effects are expected to be unidirectional, in such a way that if “unmoral acts stink” it does not necessarily mean that also “bad odors are unmoral” (see⁵⁴⁸ for a systematic discussion on this topic). In this perspective, it is theoretically relevant to assess whether the influence of disgust expectation on moral processing is associated with an influence of inappropriate behavior on disgusting experience.

Previous studies have described a causal effect of morality on purity (e.g. thoughts of cleansing)540,556,644,645, thus implying a potential bidirectional relationship between moral processing and physical disgust. To our knowledge, only Eskine et al.⁴⁸⁰ have demonstrated how description of inappropriate behavior might lead to harsher disgust ratings of gustatory stimuli, although no control was offered to see whether such influence generalized to other unpleasant experiences such as pain.

Our study solves the limitation of previous researches, by showing an effect played by inappropriate behavior on the representation of physical disgust, but not on the representation of physical pain. We believe that this is the strongest evidence thus far that our processing of inappropriate conducts taps (in simulation-like fashion) a representation of physical experience of disgust.

Differently from Eskine et al.⁴⁸⁰, inappropriate behavior didn’t affect subjective ratings. Instead, in Experiment 3, we found that galvanic response to HD (vs. LD), was stronger following inappropriate (vs. appropriate) dilemmas. Furthermore, in Experiment 4, the neural activity in the piriform cortex (often implicated in primary olfactory processing – see also results from Experiment 2) was modulated by HD (vs. LD) only following inappropriate (vs. appropriate) dilemmas. Please keep in mind that,

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although both Experiments 3-4 and the study from Eskine et al. both tested the influence of moral processing on disgust, the two paradigms differ under several dimensions (gustatory vs. olfactory disgust, unpleasantness vs. disgust rating, expectancy vs. simple-stimulation paradigm, etc.) any of which might underlie the observed discrepancies in the results.

Following Experiment 2, one could expect that in Experiment 4 moral processes would impact the disgust-related signal from dAI and MCC (Figure 22), under the assumption that inappropriate behaviors (from Experiment 4) trigger the same modality-specific information as the disgust cues (from Experiment 2). We found no evidence of such modulation, even under extremely liberal thresholds. Instead, our effects were observed at the level of the piriform cortex, which also exhibited disgust-specific responses in the analysis of the reference trials of Experiment 2, but was not modulated in medium trials by the information conveyed by the preceding cue. It should be acknowledged, however, that the neural responses elicited by physical pain and disgust in Experiment 4 were weaker than those elicited in Experiment 2 (see section 3.5.1 for a discussion on this matter).

In this view, it is still possible that inappropriate behavior might have influenced the activity of dAI and MCC, but that such modulation was not sufficiently robust to survive statistical testing. Alternatively, it is possible that inappropriate behaviors (from Experiment 4) influence different aspects of disgust representation than predictive cues (from Experiment 2), with the former tapping neural structures involved in primary olfactory experience, and the latter modulating regions involved in high-level processing of affective/somatic experiences.