'Trust Game' May Shed Light On Common Mental Illness

Aug. 7, 2008— -- Doctors are learning more about one of the most common psychiatric disorders -- and a novel type of "game" may be helping them.

Researchers at Baylor monitored subjects playing an economic trust game. What they found was that patients with borderline personality disorder (BPD), an oft-misunderstood and misdiagnosed mental illness that may affect as many as 2 percent of all Americans, exhibited distinct differences in the way they played the game -- as well as differences in brain patterns while they were playing it.

"We see this as a first step towards destigmatizing the disease," said P. Read Montague, a neuroscientist and director of the Human Neuroimaging Lab at Baylor.

BPD is characterized by a number of social difficulties, including difficulty controlling moods, impulsiveness and difficulties in relationships with other people.

To conduct their trial, the researchers had both healthy subjects and people with BPD play a trust game that involved one player, known as the "investor," give an amount of money to a second player, known as the "trustee" to invest. The investment then returned triple the amount, and the trustee chose how much to return to the investor.

Optimally, in this type of game, the trustee has an incentive to give a fair share to the investor so that they will continue to invest. If, for some reason, the trustee breaks from that pattern, they will typically try to repair that breach by giving larger returns to encourage a larger investment in the future.

While the researchers found that to be the case with the healthy subjects, they found that subjects with BPD were more likely to break the trust and were less likely to take steps to repair it and increase the amount of money they could make.

"When the borderlines play this game, cooperation breaks down and they don't repair it," said Montague. "There's a sense in which they don't perceive the right signals coming to them."

Using the brain scans, the researchers saw that an area of the brain known as the insula, which is typically triggered in games of economic fairness, was activated differently in healthy subjects and in those with BPD. In the subjects with BPD, the insula was activated similarly whether they were being dealt with fairly or not, leading the researchers to conclude that they were not picking up social cues the way healthy subjects would.