Placebo 'serotonin' increases heart rate variability in recovery from psychosocial stress

Objective: To investigate placebo effects on heart rate (HR) and heart rate variability (HRV) in recovery from a psychosocial stressor. Methods: A healthy sample underwent two mental arithmetic stress tests in one experimental session. After undergoing the baseline test, participants were randomized into control or placebo groups. Prior to the second stress test, the placebo group received an intranasal dose of 'serotonin' (placebo) with the suggestion that it would enhance recovery. HR and HRV were assessed throughout procedures. Results: There was an increase in vagally-mediated HRV in the placebo group. The change in HR did not differ between groups. Conclusions: Placebo suggestion can enhance autonomic recovery after psychosocial stress. Findings are consistent with the notion of top-down mechanisms of placebo effects, but further research would need to specifically examine the role of top-down regulatory pathways as possible mediators of placebo-induced changes in autonomic function. (C) 2015 Elsevier Inc. All rights reserved.