Expectations Modulate Heterotopic Noxious Counter-Stimulation Analgesia

The present study examined the contribution of expectations to analgesia induced by heterotopic noxious counter-stimulation (HNCS) in healthy volunteers assigned to a control group or 1 of 3 experimental groups in which expectations were either assessed (a priori expectations) or manipulated using suggestions (hyperalgesia and analgesia). Acute shock-pain, the nociceptive flexion reflex (RID-reflex), and shock-related anxiety were measured in response to electrical stimulations of the right sural nerve in the baseline, HNCS, and recovery periods. Counter-stimulation was applied on the contralateral forearm using a flexible cold pack. A priori expectations were strongly associated with the actual magnitude of the analgesia induced by HNCS. In comparison to the control condition, suggestions of hyperalgesia led to an increase in RIII-reflex amplitude and shock-pain, while suggestions of analgesia resulted in a greater decrease in RIII-reflex amplitude, which confirms that the analgesic process normally activated by HNCS can be blocked or enhanced by the verbal induction of expectations through suggestions. Changes in shock-anxiety induced by these suggestions were correlated to changes in shock-pain and RIII-reflex, but these changes did not emerge as a mediator of the association between manipulated expectations and HNCS analgesia. Overall, the results demonstrate that HNCS analgesia is modulated by expectations, either from a priori beliefs or suggestions, and this appears to be independent of anxiety processes. Perspective: This study demonstrates that a priori and manipulated expectations can enhance or block HNSC analgesia. Results also suggest that expectations might influence responses to analgesic treatments by altering descending modulation and contribute to observed deficit in pain inhibition processes of chronic pain patients. (C) 2013 by the American Pain Society