Category-based generalization of placebo and nocebo effects.

Human beings possess the adaptive ability to apply experiential knowledge to new situations. Although this generalization capability has been demonstrated in fear and reward learning, it remains unclear whether it extends to analgesic and hyperalgesic pain responses. Here, we conducted two experiments (total n = 104) to test the generalization effects of placebo analgesia and nocebo hyperalgesia. The first experiment, using a category-based conditioning paradigm in which two categories of images were used as acquisition stimuli, assessed whether pain perception can be generalized to never-seen pictures of the same category in the generalization phase. The second experiment adopted a single stimulus for each category as CS to further examine the generalization effects after learning a single exemplar. Pain ratings showed that participants reported higher pain or lower pain when the pain was preceded by novel stimuli that were conceptually similar to the previously conditioned stimuli, suggesting a generalization of analgesic and hyperalgesic pain modulation effects. These results provide novel evidence that analgesic and hyperalgesic effects on pain perception can be generalized to conceptually similar new items.