I feel your pain: Exploring the impact of state empathy on placebo and nocebo effects evoked by observational learning

Observational learning (OBL) can elicit placebo hypoalgesia or nocebo hyperalgesia if pain relief or exacerbation is observed after placebo administration. While dispositional empathy has occasionally been associated with increased placebo and nocebo responding, the contribution of situational empathy (‘state empathy’) remains elusive. This study addresses this knowledge gap using a validated experimental paradigm. Healthy individuals (n=180, 60% females) were randomized to four experimental groups (placebo-OBL, high-empathy placebo-OBL, nocebo-OBL, high-empathy nocebo-OBL) or two control groups (random-ratings OBL, no-observation). Medium pain was evoked at baseline and post-OBL with heat stimuli to both arms. Before OBL, a placebo ointment was applied to one arm. In the experimental groups, participants observed a model expressing hypoalgesia or hyperalgesia in reaction to the ointment. In the empathy groups, participants were instructed to empathize and imagine themselves in the model’s position. OBL did not alter pain intensity (F(3,176)=1.02, p=.39, ηp2=.02), although pain expectations changed in the expected direction (F(5.76,337.84)=5.81, p<.001, ηp2=.09). There were no between-group differences in empathy for the model, the magnitude of placebo hypoalgesia, or nocebo hyperalgesia (all p’s≥.19). The current study is one of only a few that have highlighted the limits of OBL-induced placebo and nocebo effects. Potential factors that could contribute to variance in OBL, including attention and cognitive load, are discussed. Increasing our understanding of OBL-induced pain changes can support the development of OBL-based interventions for (chronic) pain. Studying the contribution of empathic processes may be particularly relevant given their vital role in human interactions.