The placebo effect in pain reduction: The influence of conditioning experiences and response expectancies

We investigated the role of conditioning experiences and response expectancies in the generation of placebo effects. On 3 sequential days (Test 1, Experimental Session, Test 2), 66 female undergraduates were presented with a series of pain stimuli. For the experimental group, placebo administration (analgesic cream) was paired with a decrease in the painful stimulus. Two control groups were used to explore the relative contributions of verbally induced expectancies and contingent unconditional stimulus experiences per se. The results show that placebo-induced pain reduction can be obtained as a result of a conditioning procedure, independent of verbally induced expectancies. Mere verbal persuasion was not sufficient to elicit placebo-induced pain reduction, Irrespective of the experimental manipulations, the placebo effect was related to both reduced pain expectations and reduced fear of pain. Although conditioned placebo responses were evident at the subjective level, no placebo effects emerged at the physiological level.