Experimental Design and Procedure
cognitive reappraisal, OLP
The study was conducted at the University of Graz (Austria) and complied with all relevant ethical guidelines and regulations involving human participants and was approved by the ethics committee of the University of Graz (GZ. 39/64/63 ex 2021/22). All participants provided informed consent before participating. This study was preregistered on the German Clinical Trials Register (DRKS00029250, 08/06/2022) and conducted between June and September 2022. The CONSORT diagram is depicted in Supplementary Figure S1.The participants were invited to an fMRI study on emotional processing (no information about placebos was provided in the invitation). They were randomly assigned (random number table) to one of three groups: The Open-Label Placebo group (OLP; Each group received different instructions before the picture viewing task via a power-point presentation (14 slides with text and illustrations; no audio; fixed timing with 30 s per slide). The presentations followed the procedure of previous studiesFor the CR group, the presentation provided information about the neurobiological effects of emotion regulation/cognitive reappraisal (findings from fMRI/EEG studies). After the presentation, the participants were instructed to apply the strategy of cognitive reappraisal in the picture viewing task by imagining that the shown situations and objects are not real, but created by a special effects artist for a Halloween movie. This instruction has been successfully used beforeThe PV group viewed a presentation with information on affective neuroscience (findings from fMRI/EEG studies). Afterward, the participants received the same capsule as the OLP group. The capsule was introduced as an “MRI capsule”. It was stated that the capsule is filled with dextrose to enhance the metabolism-associated signal-to-noise ratio in the MRI (improvement of measurement). After the study participants rated the plausibility of this explanation on a scale ranging from 1 to 9 (very plausible). The average rating was After the instructions, the OLP group and the CR group evaluated their expectations concerning the effectiveness of the intervention (“What do you think? How effective will the OLP/cognitive reappraisal be in reducing your negative emotional responses to the images?” 1 = not effective; 9 = very effective). Then, the participants were brought to the MRI scanner in the adjacent room. Here, the group-specific instructions were summarized (OLP: “Please remember that the placebo you received may help you to reduce your negative emotional reactions to the images”; CR: “Please remember that the objects and situations shown in the pictures are not real, but have been created by a special effects artist”; PV: “Please remember to watch each image carefully for the entire duration of the presentation”).After the picture viewing, participants in the OLP group and the CR group were asked to rate the perceived effectiveness of the intervention (1 = not effective; 9 = very effective) and the plausibility of the rationale (1 = not logical; 9 = very logical).