Learning pain from others: a systematic review and meta-analysis of studies on placebo hypoalgesia and nocebo hyperalgesia induced by observational learning

Abstract

Observing someone experience pain relief or exacerbation after an intervention may induce placebo hypoalgesia or nocebo hyperalgesia. Understanding which factors contribute to these effects could help in the development of strategies for optimizing treatment of chronic pain conditions. We systematically reviewed and meta-analyzed the literature on placebo hypoalgesia and nocebo hyperalgesia induced by observational learning (OL). A systematic literature search was conducted in the databases PubMed, PsycINFO, Web of Science, ScienceDirect, PsycARTICLES, Scopus, and Academic Search Ultimate. 21 studies were included in the systematic review, 17 of which were suitable for meta-analysis (18 experiments; n=764 healthy individuals). The primary endpoint was the SMD for pain following placebo cues associated during OL with low versus high pain. OL had a small-to-medium effect on pain ratings (SMD 0.44; 95%CI 0.21 to 0.68; p<.01) and a large effect on pain expectancy (SMD 1.11; 95% CI 0.49 to 2.04; p<0.01). The type of observation (in-person vs. video) modulated the magnitude of placebo hypoalgesia/nocebo hyperalgesia (p<.01), whereas placebo type did not (p=.23). Finally, OL was more effective when observers’ empathic concern (but no other empathy-related factors) was higher (r=0.14; 95% CI 0.01 to 0.27; p=0.03). Overall, the meta-analysis demonstrates that OL can shape placebo analgesia and nocebo hyperalgesia. More research is needed to identify predictors of these effects and to study them in clinical populations. In the future, OL could be an important tool to help maximize placebo hypoalgesia in clinical settings.

Can observational learning reinforce open-label placebo hypoalgesia?

“…In addition, it further confirms that placebo hypoalgesia may be successfully induced by observational learning, while using videotaped model. 7,10,25,39 Furthermore, the placebo effects evoked in groups with the open-label suggestion (OLP 1 OBL and OLP) were of similar magnitude, regardless of the inclusion of video recordings. Therefore, it seems that observational learning did not facilitate the open-label placebo effect, and H2 was not supported.…”

“…In addition, it further confirms that placebo hypoalgesia may be successfully induced by observational learning, while using videotaped model. 7,10,25,39…”

“…32 However, only 1 previous study on observational learning found a correlation between expectations and pain ratings, 4 while other studies did not find such a connection. 39 Therefore, it seems that the expectations induced by social information are rarely connected to the magnitude of the placebo effects, and their role requires further investigation. Other correlational analyses revealed that empathy did not contribute to the magnitude of the placebo effect, which is in line with some previous findings 10,45 but not all of them.…”

“…8,28 Furthermore, previous studies on deceptive placebo effects have shown that observing another person experience decreased pain after placebo use caused corresponding changes in participants' pain intensity ratings. 7,10,15,20,25,39,45 The placebo effects resulting from observational learning are believed to be rooted in the acquisition of specific expectations. 17,32 Moreover, modeling of placebo effects was shown to be effective both when the model's behavior is observed directly 5,15,44 or presented in a video recording, 7,10,49,50 and the effectiveness of these 2 methods was comparable.…”

Your pain increases my pain: Exploring the effect of interpersonal synchrony on the transmission of nocebo hyperalgesia

“…The nocebo effect, a pervasive problem where negative expectancies amplify symptoms such as pain (termed nocebo hyperalgesia), concerns one such instance. While most research has focused on key mechanisms of nocebo hyperalgesia that are non-social, growing evidence indicates that social learning plays a significant role in generating maladaptive pain experiences 10,11, , with moderate to large effects on pain and expectations for pain in meta-analysis 12 .…”