Discussion
disgust reduction, OLP
RECRUITMENT, CORTEX
Research has demonstrated that OLPs can reduce emotional distressIt was found that the CR group and the OLP group gave lower disgust ratings for the negative pictures compared to the PV group. While CR had a large effect on disgust reduction (difference CR vs. PV), the effect of the OLP was medium-sized (OLP vs. PV). Similar changes in self-reports for emotional distress have been reported before in studies on cognitive reappraisalThe neuroimaging data indicated the involvement of the ventrolateral prefrontal cortex (VLPFC) during both CR and OLP treatment compared to the passive viewing of the disgusting pictures. The VLPFC has been found to be activated during the use of various strategies for voluntary emotion regulation, such as distraction, expression inhibition, and CR (see meta-analysis byParticipants of the OLP group displayed increased activity in the right VLPFC (contrast: OLP > PV). The right VLPFC plays a critical role in motor inhibition and (visual) attentionThe passive viewing of the disgusting images was associated with activity in the putamen and pallidum. This replicates previous findings of several fMRI studies that used visual disgust elicitorsIn line with this interpretation is the result concerning insula recruitment, which was more pronounced during PV relative to CR (contrast: PV > CR). The insula is part of a salience network that plays an important role in tracking emotions associated with bodily states, such as disgust, and generally for the representation of interoceptive processesTo sum up the fMRI findings it can be stated that CR increased activation in a cognitive control region (VLPFC) and reduced activation in regions that decode the salience and punishment value of stimuli (insula, putamen/pallidum). The OLP treatment also recruited the VLPFC but was not able to lower activation in the putamen, pallidum, and insula.The observed activation differences between OLP and CR imply that the placebo was a less efficient method for reducing disgust. This interpretation is also supported by participants’ efficacy ratings for the treatments. Both the expected efficacy before the picture viewing as well as the perceived efficacy after the picture viewing were higher in the CR group compared to the OLP group. This effect was large as indicated by the associated effect size measures. Further, the OLP group gave lower efficacy ratings after the picture viewing compared to before the picture viewing, whereas the ratings given by the CR group remained temporally stable. This effect might be interpreted as a sign of disappointment concerning the OLP intervention (which appeared for the participants to not work out as well as expected). A similar finding has been reported previously in a study that also administered an OLP for reducing emotional distress induced by negative picturesFinally, CR was rated as a more plausible strategy for disgust regulation than the OLP. Participants of the CR group indicated few problems in following the instructions. In contrast, some participants in the OLP group reported that they found the idea to swallow a sugar pill for reducing emotional distress to be unconvincing. In both groups (CR, OLP), ratings for the plausibility of the rationale were positively associated with the expected and perceived effectiveness of the intervention.Although the current study found OLP to be an intervention that was on average less effective than CR, half of the participants (49%) reported profiting from the non-deceptive placebo treatment (and gave efficacy ratings ≥ 5 after the picture viewing). Therefore, future studies need to identify those factors (personal, contextual) that are associated with the reactivity to OLP treatment.Some limitations of the current study should be mentioned. First, our sample included only female participants with a limited age range and educational background (with the majority being students). Therefore, our findings may not apply to other sociodemographic groups. Second, this study focused on disgust processing. Therefore, the present findings cannot be generalized to other forms of emotional distress. For example, a previous OLP study with fMRIIn sum, the current study showed CR to be a superior method for disgust regulation in healthy female participants compared to OLP, on both the subjective as well as the neurobiological level.