Distraction speeds the decay of shock-induced hypoalgesia: evidence for the contribution of memory systems in affective pain modulation.
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UNLABELLED: Previous research indicates that exposure to shock decreases thermal pain sensitivity in humans. This hypoalgesia has been attributed to a centrally mediated fear state that activates descending inhibitory pathways. Animal research suggests that distraction alters the activation of these hypoalgesic systems. To determine whether the pain memory alters the activation of hypoalgesic systems in humans, the present study examined whether a post-shock distractor attenuates shock-induced hypoalgesia. If fear-inducing shocks are represented by a limited capacity working memory system, then a distractor should speed the decay of the hypoalgesia. Healthy men were randomly assigned to 1 of 4 groups: shock-distraction, shock-no distraction, no shock-distraction, and no shock-no distraction. Following baseline pain tests, participants in the shock groups were presented with 3 brief shocks. Immediately following shock, an unexpected vibration stimulus was presented to participants in the distraction groups. Both self-report and physiological (SCL, HR) measures indicated that shock exposure resulted in fear, arousal, and decreased pain sensitivity. Consistent with prior animal studies, presentation of a post-shock distractor sped the decay of shock-induced hypoalgesia. Specifically, the distraction group exhibited significantly less shock-induced hypoalgesia compared to the no-distraction group. These findings provide additional evidence for the involvement of memory processes in the activation of descending pain inhibitory pathways. PERSPECTIVE: This study demonstrated that the presentation of a distracting stimulus immediately following 3 brief shocks attenuated shock-induced hypoalgesia in healthy human subjects. Understanding the impact of post-pain distraction on pain processing may have important clinical implications because it may influence patients' willingness to undergo future painful medical procedures.
