Nocebo Hyperalgesia, Partial Reinforcement, and Extinction

Abstract

Many studies have found evidence of conditioning-induced nocebo hyperalgesia. However, these studies have exclusively involved continuous reinforcement (CRF) schedules. Thus, it is currently unknown whether nocebo hyperalgesia can result after partial reinforcement (PRF). We tested this using electrodermal pain stimulation in healthy volunteers. Undergraduates (N = 135) received nocebo treatment under the guise of a hyperalgesic. Participants were randomly allocated to CRF, PRF, or control (no conditioning). Conditioning involved surreptitiously increasing pain stimulation on nocebo trials relative to control trials. During training, the CRF group always had the nocebo paired with the surreptitious pain increase, whereas the PRF group experienced the increase on only 62.5% of nocebo trials. In the test phase, pain stimulation was equivalent across nocebo and control trials. PRF was sufficient to induce nocebo hyperalgesia; however, this was weaker than CRF. Nocebo hyperalgesia failed to extinguish irrespective of the training schedule. Additional assessment of expectancies indicated strong concordance between expectancy and nocebo hyperalgesia. Overall, these findings suggest that once established, nocebo hyperalgesia may be difficult to disrupt. PRF may be a novel method of reducing the intensity of nocebo hyperalgesia in the clinic, which may be particularly important given its persistence.

Perspective: This study provides novel evidence that partial reinforcement results in weaker nocebo hyperalgesia than continuous reinforcement and that nocebo hyperalgesia fails to extinguish, irrespective of the training schedule. As a result, partial reinforcement may serve as a method for reducing the intensity of nocebo hyperalgesia in the clinic.

Keywords: Nocebo; conditioning; expectancy; pain; partial reinforcement.