Journal of Personality Disorders, 28, 1-12, 2014 © 2014 The Guilford Press 1 This article was accepted under the editorship of Robert F. Krueger and John Livesley. From Semmelweis University, Department of Psychiatry and Psychotherapy, Budapest, Hungary (P.P., D.F., Z.U., E.S., G.C.). Address correspondence to Patricia Polgár, Semmelweis University, Department of Psychiatry and Psycho- therapy, Balassa 6, 1083 Budapest, Hungary; E-mail: polgar.patricia@med.semmelweis-univ.hu ULTIMATUM GAME STUDY IN BORDERLINE PERSONALITY POLGÁR ET AL. ALTERED SOCIAL DECISION MAKING IN BORDERLINE PERSONALITY DISORDER: AN ULTIMATUM GAME STUDY Patricia Polgár, MD, PhD, Dóra Fogd, Zsolt Unoka, MD, PhD, Enikő Sirály, MD, and Gábor Csukly, MD, PhD The authors examined social decision-making strategies in borderline per- sonality disorder (BPD) using the Ultimatum Game (UG). They sought to extend previous findings by investigating altruistic punishment, a behavior that increases group cooperation in the long term. They tested the effect of the proposer’s facial expression on responses. BPD patients (n = 47) and healthy controls (n = 43) played the responder’s role in a series of com- puterized UG interactions, with proposers expressing positive or negative emotions. BPD patients accepted unfair offers at a higher rate compared to controls. The effect of facial expression differed in the two groups, as posi- tive expressions increased the acceptance likelihood in the control group at stakes from 20:80 to 50:50. In the BPD group, this effect was observed only at higher stakes (40:60 and 50:50). These results suggest that BPD patients exhibit altruistic punishment to a lesser extent and are less influenced by their partners’ emotional expression in the UG. Borderline personality disorder (BPD) is characterized by impaired social functioning and unstable interpersonal relationships (American Psychiatric Association, 1994). However, the underlying processes of these features are still unclear. Patients with BPD were shown to have deficits in higher or- der integration of social information (Minzenberg, Poole, & Vinogradov, 2006). BPD is associated with insecure attachment style (Agrawal, Gunder- son, Holmes, & Lyons-Ruth, 2004), high levels of early maladaptive sche- mas (Specht, Chapman, & Cellucci, 2009; Unoka, Fogd, Fuzy, & Csukly, 2011), dysfunctional beliefs, alexithymia, and reduced cognitive empathy (Guttman & Laporte, 2000; Harari, Shamay-Tsoory, Ravid, & Levkovitz, 2010; Unoka et al., 2011), rejection sensitivity (Berenson, Downey, Rafa- eli, Coifman, & Paquin, 2011; Unoka et al., 2011), and emotion dysregula- tion (Iverson, Follette, Pistorello, & Fruzzetti, 2012). Studies focusing on facial emotion recognition suggest impairments at different levels (e.g., gen- eral deficit or negativity, anger bias; for a review, see Domes, Schulze, &