Psychobiological mechanisms of impaired reward processing in chronic pain
Final Report Abstract
Chronic pain is a major problem that causes immense personal suffering and enormous socioeconomic costs. Although pain research has made great progress in the last decades, effective therapy options are still limited. More recent work emphasizes the important role of emotional and motivational processes in pain. In chronic pain, a negative hedonic shift has been described that is assumed to result in enhanced pain perception and impaired processing of reward. However, the currently available data does not allow a conclusion on whether reward processing is truly altered in chronic pain patients. Therefore, the aim of the present project was to characterize alterations in the processing of reward together with their neural correlates in patients with chronic pain. For this purpose, 30 patients with chronic back pain and 30 healthy controls participated in psychophysical experiment and functional magnetic resonance imaging (fMRI). All participants performed several tasks with different reward types (money, social, food, pain avoidance), on different components of reward (wanting, liking), and different needed behaviors (reaction time tasks, decision-making). Results of this study demonstrate that impairments in reward processing in chronic pain depend on the type of reward, the reward components, and the needed behavior to get reward. Specifically, results showed no difference in assessments that reflect the motivation to get reward in pain patients compared to controls, while patients evaluated all negative outcomes (e.g. omission of reward, pain) as more unpleasant than healthy controls. Further, patients with chronic pain rejected monetary wins more frequently compared to healthy controls, if these wins were linked to the reception of a painful stimulus. This decision-making appears driven by higher loss aversion in patients compared to controls, which is also reflected in neural correlates. Here, activation in the medial prefrontal cortex was less attenuated by loss aversion during decision-making in healthy controls compared to patients, possibly because loss aversion affected the perceived value of the combined win and reward outcome more strongly in patients. Overall, the present results demonstrate impaired reward processing in chronic pain, but results are complex and heterogenous. The exact description of such functional and dysfunctional processes is needed in the long-run for the optimization of in mechanism-based interventions for the treatment of chronic pain.
