32 available, and an up-to-date review is needed to examine how different types of learning may induce nocebo effects of different magnitudes. At the same time, other variables, such as the type of sensation (i.e., pain or itch), stimulus modality (e.g., thermal, electrical), the intensity of pain or itch stimulations, and the length of learning in different behavioral paradigms, also require a systematic examination across studies. For example, in experimental nocebo research, some nocebo conditioning paradigms include as few as four associative learning trials (Blythe et al., 2021), while others employ much longer paradigms 6,8,21. A diverse set of cutaneous sensory induction methods are also used, such as thermal 17, electrical 6,20, or laser pain stimulations 22. Such methodological choices, often meant to target specific underlying processes in nocebo experiments, can potentially influence nocebo responding and thus merit further investigation. Given the recent growth of nocebo research, we conducted a systematic review and meta-analysis of experimental nocebo studies in healthy participants to provide novel insights into distinct contributions of methodological factors in the induction of nocebo responses. We focused on cutaneous sensations, aiming to examine nocebo responses induced with comparable sensory inductions externally on the skin. First, we examined nocebo magnitudes between pain and itch and based on the learning method used. Then, we conducted subgroup analyses and meta-regression to assess how the type and intensity of stimulations, the length of learning, the timing of measurement of nocebo magnitudes, and risk of bias in studies may impact nocebo magnitudes.
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