UCLA

Humans and other social animals seem to place a positive reward value on the welfare of others. Many believe that this “prosocial inclination” is driven by empathy for others, though the mechanisms underlying this relationship remain unclear. An important subprocess within empathy is our ability to share in the internal and behavioral states of others, a process we will refer to as self other resonance. Evidence suggests that this ability is heavily driven by neural resonance, a brain mechanism in which the perception of internal states and behavior in others triggers correlated activity in motor, somatosensory and affective brain systems, potentially creating shared information states between individuals. Self-other resonance may foster prosocial inclinations by a simulation mechanism according to which the more we share in others’ states, the more we may be inclined to treat them as we would ourselves. Conversely, contextual factors that inhibit or enhance our degree of self-other resonance with others, like their group affiliation, their social distance, their race or their perceived character, also seem to modulate our prosocial inclinations towards them, suggesting common control mechanisms.

We hypothesize that individual differences in the neural correlates of self–other resonance and its control can predict individual differences in the behavioral correlates of prosociality and its modulation in response to context. We first examined which neural data during self-other resonance tasks was most informative about prosocial behavior in the Dictator Game, a task in which subjects decide how to allocate real money between themselves and 24 players (represented with a neutral-expression headshot, a name and a yearly income) of high and low incomes (Experiment 1, n=20). We then attempted to causally elucidate the relationship between self-other resonance and control by the use of a behavioral intervention (Experiment 2, n=34) and disruptive neuromodulation (Experiment 3, n=58), designed to enhance self-other resonance and disrupt top-down control, respectively. Finally, since all 78 subjects from experiments 1 and 3 underwent identical neuroimaging and behavioral protocols, we investigated gender differences in trait empathy and neural correlates of self-other resonance, including functional connectivity among regions implicated in self-other resonance and its control.

In Experiment 1, we found that individual differences in subjects’ vicarious activation in regions associated with self-other resonance (limbic system and somatosensory cortex), and regions associated with top-down control of pain, motor behavior and affect (temporoparietal junction, medial and dorsolateral prefrontal cortex) was correlated with individual differences in subjects’ prosocial decisions as well as their tendency to modulate these decisions in response to contextual information. Furthermore, we found evidence for functional connectivity between these self other resonance and top-down control areas, and found that this functional connectivity was also correlated with prosocial decisions. These findings suggest that self other resonance drives greater prosocial inclinations, while top-down control results in inhibition of prosocial inclinations, at least in the experimental setting we adopted. Indeed, disruptive neuromodulation of two putative control areas resulted in reliable increases in prosocial decisions (Experiment 3). The behavioral intervention designed to engage self-other resonance, on the other hand, did not show evidence of increasing prosocial decision-making (Experiment 2), though it did significantly alter the distribution of subjects’ offers to low-income players (increased normality and reduced variance). This null finding cannot exclude that more effective or longer interventions may indeed boost prosocial inclinations. Last, in examining gender differences, we found evidence for increased top-down control in males and increased bottom-up perceptual processing in females. This is consistent with previous findings in empathy research suggesting that females are more prone to vicariously respond to the states of others, while males are more prone to engage top-down control of affect and vicarious responding.

These results jointly suggest that self other resonance and control processes may be an important component of prosocial decision-making, by modulating the extent to which we put others’ welfare on par with our own, even when social cues typically associated with self other resonance are very limited. An important theoretical question is why self other resonance and its control seem to play such a crucial role in prosocial decision making in these conditions (when social cues are limited). We suggest that the embodied cognition framework provides a plausible functional mechanism that accounts for these findings.