Specifying Contextual Factors; Caregivers' Role in Pain Report and Placebo Effects - The role of caregivers' characteristics and nonverbal behaviours in pain and placebo effects

Abstract

In this PhD project, we investigated the role of caregivers’ characteristics, by means of caregivers’ sex/gender and social status, and their nonverbal behaviours on pain reports and placebo effects (i.e., better treatment outcomes due to expectations that effective treatment has been administrated). Our systematic review of the literature revealed that both pain patients and healthy participants reported less pain when interacting with providers of the opposite sex. Furthermore, caregivers displaying higher status, professionalism, and confidence tended to receive lower pain reports and elicit stronger placebo effects. Positive nonverbal behaviours, such as smiling, maintaining eye contact, and using open body gestures, led to lower pain reports and enhanced placebo effects. Conversely, negative nonverbal behaviours, like avoiding eye contact, not smiling, and displaying closed or defensive body gestures, increased pain reports and elicited nocebo effects (i.e., worse treatment outcomes due to a medically inactive factor).

In a dental pain experiment, we observed that the effectiveness of positive treatment information depended on the caregiver and their subtle nonverbal behaviours. Dental patients reported lower pain levels when they received positive treatment information from the dentist performing the treatment. However, the pain-reducing effects of positive information were lost when the information came from an assistant not involved in the treatment. An interview with the dentist suggested that she may have exhibited positive subtle nonverbal behaviours when delivering the information. We then explored the impact of singular nonverbal behaviours of caregivers as facial expressions, tone of voice and body movements in a pain experiment involving healthy participants. We found that the reduced-pain from pre-test to post-test was similar between all nonverbal behaviours. While our systematic review and dental pain study underscored the influence of caregiver characteristics and nonverbal behaviours on pain reports and placebo effects, the pain experiment showed no significant differences between singular nonverbal behaviours. Consequently, we concluded that examining singular nonverbal behaviours separately might underestimate the effect of nonverbal behaviours. Overall, our findings underscore the impact of caregiver characteristics and behaviours on pain reports and placebo effects. These insights carry implications for improving therapeutic interventions and patient outcomes.