Chapter 4 – Experimental learning 139 Studying the attenuation of nocebo hyperalgesia provides insights into the mechanisms that may contribute to the chronification of pain. While in the present study extinction was sufficient to attenuate nocebo hyperalgesia, counterconditioning was a more powerful intervention, reversing nocebo responses into an effect resembling placebo responses. Counterconditioning being more powerful than extinction can be explained by counterconditioning involving a paradigm that bears closer resemblance to successful exposure therapy techniques. For example, for the treatment of phobias 34,35 and anxiety 36, the initial association between the aversive stimulus and fear becomes attenuated through a procedure involving the removal of fear or threat 37. However, in the current study, extinction entailed a reduction of pain to the levels of control (moderate) pain stimulations, rather than the entire removal of these aversive stimuli. In pain paradigms it is often impossible, both experimentally and clinically, to achieve the entire removal of the aversive stimulus during extinction. In counterconditioning however, the painful stimuli were reduced to a level that was perceived as less unpleasant in comparison even to control pain stimulations, leading to a significantly larger reduction of nocebo responses. This is in line with findings by Meulders and colleagues 20 who showed that changing the valence of aversive stimuli might improve fear reduction and potentially prevent relapse. In contrast to the frequently observed lack in effectivity and durability of extinction 34,38,39, this counterconditioning finding indicates that there may be a path to attempt more active ways of minimizing learned responses. Nocebo hyperalgesia has consistently been found to be resistant to extinction 15,24,40, which may indicate an important mechanism of pain chronification. Moreover, research exploring the learning correlates and effectivity of conditioning with partial reinforcement has previously shown that ambiguous learning schedules produce durable conditioned effects 13,14,16,17, including previous partial reinforcement research on nocebo 15 and placebo effects 13. In this study, we did not find a
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