Placebo ‘serotonin’ increases heart rate variability in recovery from psychosocial stress

• Placebo suggestion can enhance physiological stress recovery.
• Placebo ‘serotonin’ increased vagally-mediated heart rate variability.
• Support for placebo-induced activation of top-down regulatory systems

ObjectiveTo investigate placebo effects on heart rate (HR) and heart rate variability (HRV) in recovery from a psychosocial stressor.MethodsA 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.ResultsThere was an increase in vagally-mediated HRV in the placebo group. The change in HR did not differ between groups.ConclusionsPlacebo 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.