Abstract
BACKGROUND: Placebo effects on pain are reliably observed in the literature. A core mechanism of these effects is response expectancies. Response expectancies can be formed by instructions, prior experiences and observation of others. Whether mental imagery of a response can also induce placebo-like expectancy effects on pain has not yet been studied systematically. METHODS: In Study 1, 80 healthy participants were randomly allocated to (i) response imagery or (ii) control imagery. In Study 2, 135 healthy participants were randomly allocated to (i) response imagery with a verbal suggestion regarding its effectiveness, (ii) response imagery only, or (iii) no intervention. In both studies, expected and experienced pain during cold pressor tests were measured pre- and post-intervention, along with psychological and physiological measures. RESULTS: Participants rated pain as less intense after response imagery than after control imagery in Study 1 (p = 0.044, etap2 = 0.054) and as less intense after response imagery (with or without verbal suggestion) than after no imagery in Study 2 (p < 0.001, etap2 = 0.154). Adding a verbal suggestion did not affect pain (p = 0.068, etap2 = 0.038). The effects of response imagery on experienced pain were mediated by expected pain. CONCLUSIONS: Thus, in line with research on placebo effects, the current findings indicate that response imagery can induce analgesia, via its effects on response expectancies. SIGNIFICANCE: The reported studies extend research on placebo effects by demonstrating that mental imagery of reduced pain can induce placebo-like expectancy effects on pain.
