A prosocial manipulation produces increases in positive affect and prosocial behavior, including those high in borderline traits

This study examined the effects—on mood and subsequent prosocial behavior—of a prosocial behavioral manipulation in individuals who varied in levels of borderline personality disorder traits. Female undergraduate participants (n = 230) were randomly assigned to either write an encouraging letter to a person experiencing hardship (“prosocial” condition) or to write a letter describing their typical day (control condition). Baseline measurements of mood were taken and compared with those obtained postmanipulation. Subsequent prosocial behavior was measured in two laboratory tasks. As expected, participants in the prosocial condition experienced more positive mood and more prosocial behavior after the manipulation, compared to the control manipulation, regardless of their level of borderline traits.