Medically vs Non-Medically Connoted Placebos in Placebo Hypoalgesia Induced by Operant Conditioning

Participants were randomly assigned to the experimental (medically or non-medically connoted placebo) groups, or their respective control groups. In the medically connoted placebo groups, an alleged activation of a sham TENS device served as the placebo intervention, while in the non-medically connoted placebo groups, a white circle displayed on a black screen was used. In the operant conditioning phase in the experimental groups, participants chose to accept or reject the placebo during each electrocutaneous stimulation series. Choosing placebo resulted in reduced pain intensity, whereas rejecting it maintained the intensity at the same level. The procedure in the control groups was analogous, however, the reinforcement was delivered randomly. In the posttest phase, participants retained the choice to accept or reject the placebo, although without any reinforcement. Pain intensity and expectation were evaluated using behavioral (NRS ratings) and physiological (ECG & EDA) measures.