ERP indicators of Self-Pain and Other-Pain Reductions to Placebo Analgesia Responding: The Moderating Role of the Fight-Flight-Freeze System

Background: This study evaluates the modulation of phasic pain and empathy for pain, induced by placebo analgesic effect during pain and empathy for pain tasks. Because pain can be conceptualized as a dangerous stimulus that generates avoidance, we evaluated how personality traits of approach and avoidance, as measured by the revised Reinforcement Sensitivity Theory Personality Questionnaire (RSTPQ, Corr and Cooper, 2016), modulate pain and empathy for pain responses. Methods: Sixty-three righthanded university student volunteers (32 women, range 18-29 years) were included. Subjective self-report ratings (self-pain and self-unpleasantness) and empathy for pain ratings (other-pain and other unpleasantness) were collected while participants underwent painful electrical stimulation or witnessed that another person was undergoing such stimulation. We induced placebo analgesia, a phenomenon specifically modulating the first-hand experience of pain, to test whether this also reduces other pain. Amplitude measures of the N1, P2, and P3 components of the ERPs, elicited by electric stimulations, were obtained during a painful control as well as during a placebo treatment expected to induce placebo analgesia. Results and Discussion: Our findings indicate that placebo treatment induced a reduction of self pain and self-unpleasantness, whereas during the empathy condition only reduction in other unpleasantness was observed. For the N1 wave, we observed that placebo treatment induced a small but significant, reduction of N1 amplitude at midline centroparietal scalp regions in state anxiety reducers during the self-pain condition. In the empathy for a pain condition, placebo treatment also produced a relative N1 amplitude reduction in other pain reducers. Additionally, in the self-pain condition, placebo treatment induced an amplitude reduction of the P2, and P3 waves in state anxiety reducers, and in participants reducing both pain ratings and state anxiety, or both unpleasantness ratings and state anxiety. Further, in the empathy pain condition, women exhibited higher P3 amplitudes than men during placebo treatment. Two separate conditional process analyses yielded that FFFS scores and the P2 and P3 amplitude reductions at the right centrotemporal region significantly influenced self-pain reduction. The moderator effects of FFFS in the relations linking P2 and P3 amplitude changes with pain reduction were both significant among low to moderate FFFS values. Conclusion: These observations are in line with the idea that lower levels of FFFS (active avoidance) scores can predict placebo-induced pain reduction. Findings are in line with the r-RST conceptualization that phasic pain is an aversive stimulus activating the active avoidance behavior to bring back the system to homeostasis. References: Corr, P. J., & Cooper, A. J. (2016). The Reinforcement Sensitivity Theory of Personality Questionnaire (RST-PQ): Development and validation. Psychological assessment, 28(11), 1427.