“Socially transmitted placebo effects”
Studies of placebo effects have demonstrated that manipulations of the interpersonal and physical treatment context can, in some cases, produce substantial effects on symptoms and behaviour and associated brain processes. Despite the robustness of these interpersonal-expectancy effects, there has been surprisingly little research demonstrating a causal link between providers’ expectations and patients’ treatment outcomes. In this study, we systematically manipulated providers’ expectations in a simulated clinical interaction involving administration of thermal pain and found that patients’ subjective experiences of pain were directly modulated by providers’ expectations of treatment success, as reflected in the patients’ subjective ratings, skin conductance responses and facial expression behaviours. Our study suggests that providers’ expectations about the efficacy of a treatment can substantially affect patients’ treatment outcomes via implicit social cues. This finding has important implications for virtually all clinical interactions between patients and providers and highlights the importance of explicit training in bedside manner when delivering information and interventions.