39: Placebo Hypoalgesia induced by Vicarious Operant Conditioning

Topic: Basic Science
Subtopic: Non-specific to any diagnosis (including studies in healthy animals), Placebo/Nocebo, Behavioral studies

Background and Aims: Operant conditioning shows that behavior can be shaped by rewards and punishments. Such consequences may also shape treatment expectations and influence how individuals respond to a placebo [1,2]. Importantly, placebo effects can also be acquired through observational learning, where observers form expectations by watching how others respond to a placebo. In most observational learning paradigms, observers typically watch a demonstrator whose placebo responses have been established via classical conditioning. The present study tested whether placebo hypoalgesia can instead be acquired through vicarious operant conditioning, in which an observer watches a demonstrator whose reactions to placebo are reinforced or punished.

Methods: Participants were randomly assigned to experimental groups (OC: operant conditioning; VOC: vicarious operant conditioning) or corresponding control groups (ROC: random OC; RVOC: random VOC). During the manipulation phase, OC participants could accept or reject placebo, with acceptance leading to reduced pain as reinforcement. VOC participants watched a demonstrator accepting (75% of trials) or rejecting (25% of trials) placebo, receiving pain reduction for acceptance (as reflected in his verbal pain ratings). ROC participants were randomly reinforced for their choices, while RVOC participants watched a demonstrator with randomly distributed reinforcement. In the posttest, participants could accept/reject placebo without any reinforcement delivered.

Results: Placebo hypoalgesia was observed in both experimental groups (OC and VOC), as participants reported lower pain intensity in placebo compared with non-placebo conditions. A similar pattern emerged in the RVOC control group. Additionally, choice ratio analyses revealed more frequent placebo selection in the VOC group and in both control groups.

Conclusions: These findings indicate that placebo hypoalgesia can be acquired through vicarious operant conditioning. Moreover, the higher frequency of placebo choices in the VOC group, but not in the OC group, suggests that distinct mechanisms may underlie directly experienced versus observationally acquired placebo effects within an operant conditioning framework.

References: (1) Adamczyk, W. M., Wiercioch‐Kuzianik, K., Bajcar, E. A., & Bąbel, P. (2019). Rewarded placebo analgesia: a new mechanism of placebo effects based on operant conditioning. European Journal of Pain, 23(5), 923-935.
(2) Bieniek, H., & Bąbel, P. (2023). Placebo hypoalgesia induced by operant conditioning: A comparative study on the effects of verbal, token-based, and social rewards and punishers. Scientific Reports, 13(1), 20346.

Presenting Author: Helena Bieniek
Submitting Author: Helena Bieniek

Senior Author: Przemysław Bąbel

IASP 2026 Global Year theme of Neuropathic Pain: No

• Justyna Brączyk: MA - Jagiellonian University
• Elżbieta A. Bajcar: PhD - Jagiellonian University
• Borysław Paulewicz: PhD - Jagiellonian University
• Przemysław Bąbel: PhD - Jagiellonian University