UC Irvine

Smiling has been shown to be beneficial in a number of social situations. One context in which smiling has not been well researched, however, is within physical health and health-relevant outcomes. The small amount of research in this area has found that smiling may buffer the cardiovascular effects of acute pain. The goals of this dissertation were to 1) investigate smiling in the context of physical and social pain and 2) examine potential mediators (orbicularis oculi activation in Study 1 and positive affect in both studies) that may underlie the connections between smiling and acute pain. In Study 1, participants were randomly assigned to make Duchenne (genuine) smiles, grimaces, or neutral facial expressions during two acute physical pain tasks. Cardiovascular responses (heart rate, respiratory sinus arrhythmia, and pre-ejection period) were measured at baseline, during the tasks, and after the tasks. Pain threshold, pain tolerance, and self-reported pain were also measured. Results showed that trajectories across cardiovascular variables of interest did not significantly differ between the facial expression conditions. There were also no significant differences in pain tolerance or self-reported pain among the conditions. However, participants who made Duchenne smiles during the cold pressor had significantly higher pain threshold levels than participants who made grimaces, although there were no differences between either of these groups and the neutral facial expression condition. Furthermore, some evidence was found to support PA and orbicularis oculi activation as mediators of smiling and outcome variables. In Study 2, participants were randomly assigned to make Duchenne smiles or neutral facial expressions while they were included or excluded during Cyberball, a task that has been found to reliably elicit feelings of social exclusion. Results showed that participants who made Duchenne smiles while being excluded from Cyberball had significantly different heart rate trajectories than participants who were making neutral facial expressions. There were no differences in respiratory sinus arrhythmia, pre-ejection period, or self-reported pain between conditions. No evidence was found for positive affect as a mediator between smiling and outcome variables. Taken together, these studies provide some evidence that smiling during physically or socially painful situations might be beneficial.