Feeling excluded no matter what? Bias in the processing of social participation in borderline personality disorder

Background: Patients with Borderline Personality Disorder (BPD) feel ostracized even when they are included. This might be due to a biased processing of social participation in BPD. We examined whether patients with BPD also process social overinclusion in a biased manner, i.e., whether they feel ostracized even when the degree of social participation is increased. Methods: An EEG-compatible version of Cyberball was used to investigate the effects of inclusion and overinclusion (33% vs. 45% ball receipt) on perceived ostracism, need threat and P3 amplitude, an EEG indicator for expectancy violation. Twenty-nine patients with BPD, 28 patients with Social Anxiety Disorder (SAD) and 28 healthy controls (HC) participated. Results: The P3 amplitude was enhanced for patients with BPD and SAD compared to HCs independent of condition. Both patient groups reported more perceived ostracism relative to HCs in the inclusion but not in the overinclusion condition. Only patients with BPD reported stronger need threat in both conditions. Conclusions: The EEG results imply that being socially included violates the expectations of patients with BPD, irrespective of the actual degree of social participation. However, when overincluded, patients with BPD no longer feel ostracized. Except for need threat, patients with SAD might show a comparable bias in the processing of social participation as patients with BPD. Keywords: Borderline personality disorder, Social anxiety disorder, Social cognition, Social participation, Overinclusion, Event-related brain potential