'Trust Game' May Shed Light On Common Mental Illness

A brain test known as the "trust game" fosters understanding of the condition.

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.

This made it difficult to determine how the subjects with BPD actually felt about how they were dealt with in the game, said Montague. "They probably see all gestures as being threatening and grossly unfair."

Montague expressed the hope that his study, which appears in the most recent issue of Science, would help people understand that BPD has biological origins, and is not the result of someone being difficult.

"These have not traditionally been considered organic problems with the brain," he said.

He also speculated that this study might help with diagnosis and treatment of BPD in the future.

While he called the findings interesting, Dr. Donald Black, a psychiatrist at the University of Iowa who frequently treats patients with BPD, expressed skepticism regarding how soon, if at all, the study's results could be put into practice.

"It's a potentially important finding, but right now it's at the level of a research finding that is unlikely to have a practical implication anytime soon."

At the same time, he hoped it would bring more attention to the illness.

"I don't want to minimize the importance either, because BPD…is a brain disorder and probably has a genetic basis as well," he said. "A lot of psychiatrists and researchers tend to trivialize it, but it's widespread and pretty disabling.

"We need better ways to treat these patients. I think this study is consistent with that viewpoint and may spur additional research."

A Common Illness, Commonly Ignored

Much of the difficulty in getting doctors to treat BPD, according to Black, lies in the fact that there is no specific pill or course of treatment.

"That tends to make doctors uncomfortable," he said. "They often prefer diagnoses that are associated with specific treatments."

Also, said Black, because of the constellation of symptoms that can affect patients with BPD, the doctor may diagnose it as something else, like bipolar disorder or major depression.

"I think because of the constellation of symptoms that it has, to some doctors, suggests other conditions," he said. "From my perspective, those doctors are certainly picking out the various pieces of the puzzle, but they're not assembling the puzzle. They're seeing various pieces, not the whole thing."

Black said that while the origins of BPD are unknown, there is likely a strong genetic component. The Baylor study, he said, is only the most recent of a series of studies that show BPD to have a biological explanation.

And Montague is hopeful that people will quickly understand that BPD is not the fault of the patient.

"The content of what we found was remarkable and very clear," he said.

"It's a real problem. It's just like…schizophrenia. You wouldn't blame someone who is schizophrenic for acting paranoid.

"I think it would be hard to say that they're being willfully difficult at this point."