Interindividual differences in anhedonia moderate antidepressant placebo responses on heart rate in healthy individuals

Abstract

BackgroundAntidepressant placebos and, more generally, positive treatment expectations, have been shown to alter positive and negative affect in prior studies. However, much of this work has heavily relied on self-report measures which are prone to demand effects in the context of explicit expectation manipulations. In addition, there is little knowledge about personality variables which moderate antidepressant placebo responses and may help us identify individualized and targeted interventions. MethodsInert pills were administered to N=56 healthy participants and treatment expectations were manipulated by labeling each pill as either an inactive placebo or an active antidepressant. Thereafter, participants underwent an experimental induction of depressed mood with a musical Velten approach and their affective states were assessed via ratings and heart rate. Furthermore, trait anhedonia was measured as a depression-related personality variable which may moderate antidepressant placebo responses. ResultsWhile the depressed mood induction led to a general reduction of self-reported positive affect, antidepressant treatment expectations reduced cardiac slowing to depressed mood selectively in high vs. low anhedonic subjects. LimitationsNo main effects of expectation manipulation were revealed, but an interaction with regard to cardiac response involving trait anhedonia not paralleled by self-reports. ConclusionThe present findings suggest that individuals with higher levels of trait anhedonia may benefit more from antidepressant placebo effects than low anhedonic individuals, and stress the importance of investigating placebo responses beyond self-reports at the physiological level.