Does monetary reward operantly enhance pain sensitivity over time? An experiment in healthy individuals

AIM: Operant conditioning has long been believed to influence the pain experience through a psychological reward pathway. This study was formulated to test the hypothesis that pain sensitivity may be enhanced >3 months if a monetary reward works as a reinforcement. METHODS: Forty healthy subjects volunteered to participate in this study. The subjects repeatedly underwent pain testing via mechanical stimuli, and they rolled dice three (or six) times to gain money at the following five time points: baseline, three reinforcement sessions, and last session. The payoff was determined by roll of the dice. The subjects were instructed to roll the dice into a masked stand three times per session and informed that no one monitored the number of dice actually appeared. The subjects were also informed that they could roll the dice another three times when they reported strong pain during reinforcement sessions. RESULTS: The amount of individual payoff had significantly increased at last session compared with the values obtained at baseline; however, no changes were identified in terms of the pain ratings for mechanical stimuli during all sessions. CONCLUSION: The results suggest that the psychological reward pathway does not always involve pain perception, and it is difficult to conclude whether pain sensitivity is operantly changed through the monetary reward in healthy individuals. Further investigation is required.