Placebo Analgesia Does Not Reduce Empathy for Naturalistic Depictions of Others’ Pain in a Somatosensory Specific Way

Abstract

The shared representations account postulates that sharing another’s pain recruits underlying brain functions also engaged during first-hand pain. Critically, direct causal evidence for this was mainly shown for affective pain processing, while the contribution of somatosensory processes to empathy remains controversial. This controversy may be explained, however, by experimental paradigms that did not direct attention towards a specific body part, or that did not employ naturalistic depictions of others’ pain. In this preregistered fMRI study, we aimed to test whether causal manipulation of first-hand pain affects empathy for naturalistic depictions of pain in a somatosensory-matched manner. Forty-five participants underwent a placebo analgesia induction in their right hand and observed pictures of other people’s right and left hands in pain. We found neither behavioral nor neural evidence for somatosensory-specific modulation of pain empathy. However, exploratory analyses revealed a general effect of the placebo on empathy, and higher brain activity in bilateral anterior insula when viewing others’ right hands in pain (i.e., corresponding to one’s own placebo hand). These results refine our knowledge regarding the neural mechanisms of pain empathy, and imply that the sharing of somatosensory representations seems to play less of a causal role than the one of affective representations.

Different priming effects of empathy on neural processing associated with firsthand pain and nonpain perception

“…More directly, by investigating the effect of causal manipulation of firsthand pain on empathy for pain, researchers observed that the firsthand placebo analgesia in the participant's right hand resulted in a comparable reduction of unpleasantness ratings for others' pain in both hands instead of a localized reduction for the right hand only. 56 This further suggests that shared affective representations play more of a role during empathy for pain compared with shared somatosensory representations.…”

“…31 Therefore, our result indicates that affect sharing plays a prominent role in empathy for pain, which coincides with recent functional magnetic resonance imaging (fMRI) studies investigating the shared representations between empathy for pain and firsthand pain. [55][56][57] For example, the activations in the AI and aMCC were stronger while participants observed others' facial expressions of genuine pain versus pretended pain; more importantly, the increased activation in the AI was selectively correlated with unpleasantness ratings for others' pain. 55 These results suggest that, in addition to the responses triggered by perceptual salience, the empathy-related brain responses also reflect the sharing of others' actual affective states triggered by pain.…”

Placebo Analgesia Reduces Costly Prosocial Helping to Lower Another Person’s Pain

“…The placebo groups’ belief in the effectiveness of the medication (Manipulation Check 3) was analyzed by calculating three paired-samples t tests comparing two of the three time points (before conditioning, after conditioning, after the session). Although these analyses were preregistered as exploratory, they were also employed in our previous studies using a very similar placebo analgesia induction with a gel instead of a pill (Hartmann, Riva, et al, 2021; Hartmann, Rütgen et al, 2021). On the basis of these studies, we expected a strong belief in the medication and an increased belief from before to after conditioning (see the Supplemental Material for exact criteria).…”

“…To measure whether the placebo effect lasted until the end of the session (Manipulation Check 5), we compared the postexperimental rating about how much pain was felt on average in the pain task using a t test with the index of pain ratings (pain – no pain) as the dependent variable and group (placebo, control) as a between-subjects factor. This check was not preregistered but was also employed in our previous studies (Hartmann, Riva, et al, 2021; Hartmann, Rütgen et al, 2021).…”

“…A series of experimental studies has shown that individuals whose firsthand pain was reduced by placebo analgesia (i.e., the belief that an inert treatment acts as a potent painkiller) showed reductions in self-reported pain empathy and decreased activation in key areas of the brain’s affective “pain empathy network” (Rütgen et al, 2021; Rütgen, Seidel, Riečanský, & Lamm, 2015; Rütgen, Seidel, Silani, et al, 2015; Vecchio & de Pascalis, 2021). Importantly, follow-up studies investigating whether these effects extend to the somatosensory system (using administration of a placebo gel to a selected body part rather than a pill affecting pain processing in a systemic fashion) did not find effects (Hartmann, Riva, et al, 2021; Hartmann, Rütgen et al, 2021). Of note here is that placebo mechanisms in firsthand pain (Petrovic et al, 2002; Zubieta et al, 2005; Zubieta & Stohler, 2009) and pain empathy (Rütgen et al, 2018, 2021; Rütgen, Seidel, Silani, et al, 2015) have been linked to an upregulation of the endogenous opioid system.…”