Imagine watching a video of a hypodermic syringe slowly and deliberately piercing a human hand. Despite knowing that the hand belongs to someone else, would you wince and reflexively withdraw your hand, or shrug and stay put? Would you empathize with the person getting pierced? If so, what does your reaction reveal about your moral psychology? The dual-process model of dilemma judgments (Greene et al., 2001) suggests that when people face dilemmas where causing harm saves lives, rejecting such harm (despite not saving lives) reflects other-oriented affective processing. In contrast, judgments to accept harm (thereby maximizing outcomes) reflect cognitive evaluations of outcomes. On such dilemmas, rejecting harm is said to uphold deontological morality, where the morality of actions derives from their intrinsic nature (Kant, 1785/1959), whereas accepting harm is said to uphold utilitarian morality, where the morality of actions derives from their outcomes (Mill, 1861/1998). Although considerable evidence supports the dual process model (e.g., Bartels, 2008; Amit and Greene, 2012; Conway and Gawronski, 2013; Gleichgerrcht and Young, 2013; cf. Kahane, 2015), some theorists have questioned whether the affective processing involved in harm-rejection truly reflects other-oriented concern. Affective reactions to harm in dilemma judgments may reflect self-focused emotions centered on causing harm, rather than genuine concern generated by others in pain (Miller et al., 2014).

When people know that others are experiencing pain, sensorimotor and affective systems in their brains respond as though they are personally experiencing pain (Singer et al., 2004; Avenanti et al., 2005; Lamm et al., 2011). This phenomenon, called neural resonance (Zaki and Ochsner, 2012), has also been documented for disgust (Wicker et al., 2003; Jabbi et al., 2007), emotions (Carr et al., 2003; Pfeifer et al., 2008), and motor behavior (Fadiga et al., 1995). A key moderator for the presence or absence of activity in sensorimotor circuits seems to be the direct observation of others experiencing pain (Avenanti et al., 2005). When others’ pain is communicated through symbolic cues (e.g., lightning bolts) rather than direct observation, affective circuits are activated, but sensorimotor circuits are not (Singer et al., 2004).

Although researchers conceptualize neural resonance as a component of empathy (Zaki and Ochsner, 2012), they have primarily examined immediate reactions to real-time stimuli, such as smiling faces or video clips of hands getting pierced by needles, rather than personality traits or decision-making tendencies in unrelated contexts. Yet, recent findings suggest that individual differences in neural resonance predict other aspects of an individual’s traits and behavior. Specifically, neural resonance for pain correlates with peoples’ tendency to take others’ perspectives and feel distressed by harm to others (Avenanti et al., 2009). Neural resonance for pain also correlates with charitable donations (Ma et al., 2011), helping behavior (Hein et al., 2011; Morelli et al., 2014), and generosity in economic games where strategic giving does not play any role (Christov-Moore and Iacoboni, 2016). Since correlation is not causation, we have further tested the meaning of these correlations with disruptive brain stimulation, showing that it is possible to modulate generosity by stimulating brain areas whose activity correlates with offers (Christov-Moore et al., 2017). Furthermore, deontological response tendencies on moral dilemmas correlate with empathic concern and perspective-taking (e.g., Conway and Gawronski, 2013; Gleichgerrcht and Young, 2013). These findings suggest that the neural mechanisms associated with pre-reflective reactions to others’ internal states may also be relevant to moral decision-making.

We propose that people who show greater neural resonance with the pain of others should evince stronger tendencies to reject harm in moral dilemmas, in line with the dual-process model (Greene et al., 2001). This finding would clarify that internal representations of others’ states (rather than just self-focused emotions) contribute to moral dilemma judgments. Such effects should pertain only to harm-rejection (deontological) response tendencies, which are linked to affective processing, rather than outcome-maximization (utilitarian) response tendencies, which are linked to cognitive processing (Conway and Gawronski, 2013). To examine this possibility, we employed process dissociation (PD, Jacoby, 1991) to disentangle the impacts of harm-rejection and outcome-maximization tendencies on conventional relative dilemma judgments (for a review of PD, see Payne and Bishara, 2009).

In the current work, we recorded participants’ brain activation while they watched videos of needles piercing hands (versus hands gently touched with a Q-tip). A month later or more, participants completed the PD moral dilemma battery, containing 10 moral dilemmas, each with two versions (Conway and Gawronski, 2013). Each dilemma entails causing harm to achieve a particular outcome: incongruent dilemmas correspond to conventional relative moral dilemmas where causing harm maximizes outcomes (hence deontological and utilitarian considerations conflict); congruent dilemmas involve causing harm that does not maximize outcomes (so deontological and utilitarian considerations align – both suggest rejecting harm). Participants indicated whether each harmful action was appropriate or not appropriate. By applying participant responses to both kinds of dilemmas to a processing tree (see Figure 1), we can mathematically represent the probability of accepting or rejecting harm in each case, and algebraically combine these equations to solve for two previously unknown variables: deontological inclinations (reflecting a pattern of consistently rejecting harm regardless of whether doing so maximizes outcomes), and utilitarian inclinations (reflecting a pattern of maximizing outcomes, whether or not doing so entails causing harm).

Conway and Gawronski (2013) found that deontological response tendencies uniquely correlated with measures of other-oriented concern, such as empathic concern and perspective-taking (Davis, 1983) and were uniquely increased when viewing photos of the victims of harm, clarifying similar findings on conventional dilemma judgments (e.g., Bartels, 2008; Gleichgerrcht and Young, 2013). Conversely, utilitarian response tendencies uniquely correlated with measures of cognitive processing, such as need for cognition (Epstein et al., 1996), and are uniquely impaired by cognitive load, again clarifying similar findings on relative judgments (e.g., Greene et al., 2008; Moore et al., 2008). Meta-analytic results indicated that deontological and utilitarian response tendencies are typically uncorrelated, but each correlates with conventional relative dilemma judgments in opposite directions (Friesdorf et al., 2015), suggesting that the PD parameters reflect two independent response tendencies that jointly influence conventional relative dilemma judgments.

Given research suggesting that deontological dilemma response tendencies reflect relatively affective other-oriented concern, whereas utilitarian dilemma response tendencies reflect relatively cognitive outcome-focused processing, we predicted that when viewing others in pain, activation in brain regions associated with pain processing would predict deontological, but not utilitarian, response tendencies. However, if Miller et al. (2014) are correct that deontological decisions primarily reflect self-focused concerns over causing harm, rather than other-focused affective processing regarding witnessing harm, then brain activation while witnessing others in pain (pain one did not cause) should not predict dilemma response tendencies.

Moreover, we aimed to clarify the nature of other-oriented concern involved in deontological dilemma decisions. As mentioned above, neural resonance for pain recruits both affective (anterior cingulate, medial prefrontal cortex, and anterior insula) and sensorimotor (ventral premotor cortex, inferior parietal lobe, and primary motor cortex) neural systems to different extents depending on stimuli and context (reviewed in Lamm et al., 2011). We employed stimuli known to activate both sensorimotor and affective systems (Avenanti et al., 2005; Bufalari et al., 2007) – videos of painful stimuli applied to others (Avenanti et al., 2005) – to examine which system best predicts deontological dilemma response tendencies, rather than employing stimuli known to selectively activate affective but not sensorimotor networks (as in Singer et al., 2004), which would prevent us from testing these hypotheses against one another.

If affective systems best predict deontological tendencies, this may suggest that deontological decisions primarily reflect general affective responses to others’ pain. On the other hand, if sensorimotor circuits best predict deontological tendencies, this may suggest that deontological decisions are partially grounded in participants’ previous personal perceptual and motor experiences of pain. In other words, witnessing a needle pierce someone else’s hand may lead participants to imagine, albeit likely implicitly, how others experience the physical sensation of having their hand pierced. Such physiological representations of others’ pain may lead participants to reject actions that cause others pain – such as endorsing deontological moral dilemma judgments. Note that whereas previous functional magnetic resonance imaging (fMRI) dilemma research examined brain activation as participants completed the dilemma task itself (e.g., Greene et al., 2001, 2004), we examined brain activation in response to unrelated stimuli – the needle task – and used this activation to predict dilemma responses made over 1 month later.

To recapitulate, this study tested two hypotheses. First, we examined whether neural responses to witnessing another person experience pain predicted subsequent deontological (but not utilitarian) dilemma response tendencies. Second, we investigated the nature of the functional processes associated with deontological tendencies: whether they are best predicted by systems involved in general affective processing, or by systems involved in the sensorimotor processing of watching others in pain.

Participants’ scores on the moral dilemma battery were process dissociated to produce the Deontological Parameter (M = 0.45, SD = 0.087), and the Utilitarian Parameter (M = -0.41, SD = 0.163). Neither scale violated the assumption of normality as verified via a Shapiro–Wilk’s test (Supplementary Figure S1).

The contrast Pain > Touch yielded clusters of activation consistent with prior studies on empathy for pain (Lamm et al., 2011). These clusters were located in visual cortex, inferior and superior parietal cortex, motor cortex, inferior premotor cortex, dorsolateral prefrontal cortex, anterior cingulate, thalamus, and others (see Figure 2 and Supplementary Table S1). The deontological PD parameter (reflecting harm-aversion dilemma judgments) correlated with BOLD signal changes in the left inferior frontal gyrus, pars opercularis, (see Figure 3 and Table 1). As predicted, there were no correlations between the utilitarian PD parameter (reflecting outcome-maximization judgments) and BOLD signal changes for the contrast Pain > Touch.

This study is the first attempt to assess the relationship between the BOLD signal while people witness others in pain and those same peoples’ later response tendencies in hypothetical moral dilemmas. It belongs to a larger project on the relationships between type 1, pre-reflective responses to the internal states of other people, and type 2, reflective prosocial decisions that also includes two recent studies (Christov-Moore and Iacoboni, 2016; Christov-Moore et al., 2017). A broad array of brain regions responded to the pain video task, but of those, later harm-rejection (deontological) judgment tendencies were only predicted by activation in a sensorimotor area (IFG) associated with observing, imitating, and understanding the motor behavior of others (Iacoboni, 2009; Urgesi et al., 2014), their internal states (Carr et al., 2003; Lamm et al., 2011), and the broader construct of empathy (Carr et al., 2003; Lamm et al., 2011) and empathic accuracy (Paracampo et al., 2017). In contrast, areas associated with affective processing of empathy for pain, such as the anterior cingulate or anterior insula (Singer et al., 2004), did not predict deontological responses, despite those areas showing activation during the pain video task. As expected, no brain activation while witnessing pain correlated with outcome-maximization (utilitarian) judgment tendencies. These findings cannot reflect priming effects from the pain video task, as participants completed the dilemma battery at least 1 month following the scanner session. Together, results suggest that people who demonstrate greater sensorimotor empathy for observed pain in others are more likely to avoid causing harm (but not maximize outcomes) in hypothetical moral dilemmas.

These results, while correlational, support the hypothesis that deontological response tendencies primarily reflect genuine concern for others generated by witnessing pain, rather than self-focused emotional reactions to causing pain – after all, participants passively witnessed, rather than actively caused, the painful needle stimuli (Miller et al., 2014). These findings align with research linking deontological response tendencies to other-oriented processing, such as empathic concern and perspective-taking (e.g., Bartels, 2008; Conway and Gawronski, 2013; Gleichgerrcht and Young, 2013), thereby corroborating the dual-process model (Greene et al., 2001). However, these findings do not rule out the possibility that self-focused concerns regarding causing harm independently influence deontological response tendencies via mechanisms not captured in the current paradigm (Reynolds and Conway, in press).

Furthermore, these findings suggest the possible nature of the functional processes supporting other-oriented affective responses that lead to deontological choices. We employed stimuli known to elicit activation in circuits involved in both sensorimotor and general affective processing, and indeed found activation in both regions during the pain video task. However, only activation in the posterior inferior frontal cortex (pIFC) – associated with sensorimotor processing but not general affective processing – predicted subsequent deontological response tendencies. Past work shows that the pain video used here modulated transcranial magnetic stimulation (TMS)-induced motor evoked potentials (MEPs), an index of motor excitability, providing clear evidence for a sensorimotor component to empathy (Avenanti et al., 2005). TMS-induced MEP modulation while perceiving others’ hand actions, however, disappears when pIFC and neighboring areas are transiently disrupted by repetitive TMS (Avenanti et al., 2007). These findings suggest that activity in pIFC and neighboring areas is crucial for the sensorimotor component of empathy (Avenanti et al., 2005). Hence, we believe the correlation between deontological tendencies and pIFC activity in the current study is mainly driven by the pIFC’s role in the sensorimotor component of empathy. Furthermore, the role of the IFG in recognizing and understanding the behavior of others (Urgesi et al., 2014) as well as accurately assessing their internal states or empathic accuracy (Paracampo et al., 2017) is consistent with the notion that the pIFC integrates or provides links between high- and low-level empathic processes like neural resonance and moral decision-making.

We propose that the sensorimotor and affective mechanisms used to process one’s own pain also react to abstract and non-sensory harm to others, such as vivid images of pain – including mental images conjured when considering hypothetical moral dilemma scenarios. The more individuals recruit non-agent-specific pain representations in response to others’ suffering, the more likely they are to personally appreciate how others will experience harm. People who especially engage in such implicit representations appear especially likely to recoil from inducing pain on subsequent moral dilemma tasks (i.e., reject causing even harm that maximizes outcomes). Such findings are consistent with evidence that making harm vivid reduces willingness to directly inflict harm in moral dilemmas (e.g., Bartels, 2008), specifically through increased deontological inclinations (Conway and Gawronski, 2013), and that impairing visual processing reduces deontological judgments (Amit and Greene, 2012). However, the present findings are the first to suggest that the embodied consideration of other people’s pain at a sensorimotor level influence moral decision-making.

Obviously, these findings do not challenge the engagement of affective systems in moral dilemma judgment tendencies. Indeed, we should exercise caution extrapolating from the current limited sample. The lack of brain-behavior correlation with affective systems may reflect a false negative due to insufficient power, or else indicate that perhaps affective processing in moral dilemmas is relatively insensitive to individual differences in judgment tendencies. Furthermore, because no subjective evaluation was conducted regarding subject’s internal state while observing the needle stimuli, we cannot be sure that the task we used consistently tapped into concern for others, rather than self-focused emotional/sensorimotor experience. The relationship between these sensorimotor representations and dilemma responses may not be the one hypothesized here. However, the vicarious nature of this sensorimotor processing as well as past studies showing correlations between neural activity during similar tasks and other-oriented processes like empathy and pro-sociality mitigate this concern.

As predicted, these results failed to indicate an association between brain activation while witnessing harm and utilitarian response inclinations. This pattern meshes with previous findings suggesting the utilitarian responses primarily reflect abstract cognitive considerations of overall well-being, rather than a concrete focus on harm (e.g., Greene et al., 2008; Moore et al., 2008; Conway and Gawronski, 2013; cf. Kahane, 2015). Future research might profitably examine whether the utilitarian PD parameter correlates with brain activity when participants engage in theory of mind reasoning, mathematical calculations, or other abstract cognitive operations.

The current findings bolster the growing evidence that individual variability in sensorimotor and affective neural resonance predict differences in decision-making (Hein et al., 2011; Ma et al., 2011; Morelli et al., 2014; Christov-Moore and Iacoboni, 2016). Thus far, researchers have investigated this link only in the realm of prosocial decision-making (decisions involving potential gains); the current findings extend this relationship to moral dilemma judgments (decisions involving potential losses). Whereas some studies have implicated affective areas like the anterior insula in motivating prosocial decisions (Hein et al., 2011), others have implicated sensorimotor areas like the superior parietal lobe (Christov-Moore and Iacoboni, 2016) and SII/pIFC (Ma et al., 2011). One interpretation of this pattern suggests that general affective processing may be more important for motivating prosocial behavior rather than harm avoidance, whereas sensorimotor processing features for both. Alternatively, it remains possible that the current stimuli do not reveal the full extent to which general affective processing impacts harm-avoidance judgments. Consider that the videos we employed showed a close-up of hands getting pierced, without accompanying stimuli associated with witnessing others in pain (e.g., facial grimacing, cries of pain). Perhaps including such cues may provide increased evidence for the impact of general affective processing on dilemma decision-making. It remains likely that the relative contributions of affective or sensorimotor processes depend on multiple factors.

These findings are the first to demonstrate that, upon witnessing others in pain, brain activation in sensorimotor circuits involved in processing pain in the self predicts subsequent inclinations to avoid causing harm in moral dilemmas (even to maximize outcomes). Such findings clarify the importance of genuine concern for others in dilemma judgments, corroborate the dual process model, and provide further evidence for the utility of PD in dilemma decision-making. Moreover, these findings suggest a role for the embodied sensorimotor processing of harm when making moral dilemma decisions. People with stronger internal sensorimotor representations of others’ physical pain may be especially unwilling to visit harm on others, even for a good cause.

LC-M developed the study concept. All authors contributed to the study design. Testing and data collection were performed by LC-M and PC. LC-M and PC performed the data analysis and interpretation under the supervision of MI. LC-M and PC drafted the manuscript, and MI provided critical revisions. All authors approved the final version of the manuscript for submission.

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.