Background & Aims
Impaired reward processing has been implicated in the development and maintenance of chronic pain (Mitsi & Zachariou, 2016; Löffler et al., 2022). Accordingly, it has been hypothesized that alterations found in neural reward circuitries manifest in a negative hedonic shift that is characterized by decreased sensitivity to rewarding stimuli and increased sensitivity to aversive stimuli (Borsook et al. 2016). However, data that relates behavioral and perceptual changes to such altered neural processing of reward is scarce. In this study we aimed to compare both, perceptual and motivational aspects of reward processing, between individuals with and without chronic back pain, to gain insights into mechanisms of reward processing.
Methods
We assessed 30 individuals with chronic back pain and 30 pain-free participants to determine potential alterations of the motivation to obtain reward and avoid aversive stimuli and the hedonic experience of rewards and aversive stimuli. We used variations of an incentive delay task to evaluate the motivational and hedonic aspects of reward processing for appetitive and aversive (pain) stimuli. In addition, we included a task that focused on how participants trade-off pain against rewards. During execution of the tasks, we used functional magnetic resonance imaging and used blood oxygen level dependent responses to capture neural correlates of the different aspects of reward processing.
Results
We report evidence on domain-specific processing of appetitive and aversive stimuli in individuals with and without chronic back pain and compare different aspects of reward processing between the experimental groups. We report differential effects of the clinical state on success rates as a measure of the motivation to obtain rewards or to avoid aversive stimuli (wanting) and ratings on a visual analogue scale as a measure of hedonic experience (liking) induced by the rewarding stimuli. Moreover, we show how individuals with and without chronic pain trade-off pain against monetary rewards and associate their behavior with endogenous modulation of the perception of pain.
Conclusions
To leverage knowledge on alterations of reward processing in chronic pain it is crucial to understand which mechanisms need to be targeted for the development of new and enhancement of established treatment strategies. We highlight the importance of differentiating motivational and perceptual aspects of reward processing and their interaction. Future studies need to further assess how differential processing of rewards and aversive stimuli relate to learning mechanisms in the context of pain.
References
Borsook, D., Linnman, C., Faria, V., Strassman, A. M., Becerra, L., & Elman, I. (2016). Reward deficiency and anti-reward in pain chronification. Neuroscience and Biobehavioral Reviews, 68, 282–297. https://doi.org/10.1016/j.neubiorev.2016.05.033
Löffler, M., Levine, S. M., Usai, K., Desch, S., Kandic, M., Nees, F., & Flor, H. (2022). Corticostriatal circuits in the transition to chronic back pain: The predictive role of reward learning. Cell Rep Med, 3(7), 100677. https://doi.org/10.1016/j.xcrm.2022.100677
Mitsi, V., & Zachariou, V. (2016). Modulation of pain, nociception, and analgesia by the brain reward center. Neuroscience, 338, 81–92. https://doi.org/10.1016/j.neuroscience.2016.05.017