In the first study of its kind, psychologists have used an economic game to investigate the behaviour and brain processes of people diagnosed with a personality disorder.
Brooks King-Casas and colleagues recruited dozens of people with borderline personality disorder (BPD) to play the role of trustee in an economic game. People with this disorder tend to have unstable personal relationships and difficulty regulating their emotions. Healthy participants were recruited to play the part of investor and/or trustee.
Over several rounds, the game involved the investor choosing how much money to pass to the trustee. The investment was automatically tripled and then the trustee had to decide how much money to pass back to the investor. For maximum returns, both parties need to cooperate. If the trustee is unfair in the returns he gives back, the investor will likely reduce his investments on future rounds, meaning less profit for everyone.
The researchers found that cooperation broke down when a person with BPD played the role of trustee. They failed to recognise smaller investments as a sign that the investor was losing trust. Healthy trustees, by contrast, responded to a distrustful investor by increasing the returns they gave, thereby coaxing back the investor's trust and provoking a return to larger investments.
Brain scans taken while the participants played the role of trustee showed that healthy participants, but not participants with BPD, showed greater activity in the anterior insula as investments reduced in size (this is a brain region known to be involved in fairness, as well as sensing the body's internal states). Perhaps because of their low expectations for how others will treat them, the participants with BPD didn't appear to recognise a low investment as unfair. Consequently, they didn't attempt to restore the investor's trust, thus leading to a collapse of cooperation.
In a commentary on the study, published in the same journal issue, Andreas Meyer-Lindenberg welcomed this pioneering use of an economic game for the study of mental health. "The correspondence of these brain findings to current psychotherapeutic practice is remarkable," he also noted. "The most effective treatment of borderline personality disorder, dialectical behaviour therapy, is based on the assumption that patients lack skills in interpersonal regulation, and attempts to build these abilities."
B. King-Casas, C. Sharp, L. Lomax-Bream, T. Lohrenz, P. Fonagy, P. R. Montague (2008). The Rupture and Repair of Cooperation in Borderline Personality Disorder Science, 321 (5890), 806-810 DOI: 10.1126/science.1156902
A. Meyer-Lindenberg (2008). PSYCHOLOGY: Trust Me on This Science, 321 (5890), 778-780 DOI: 10.1126/science.1162908