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SCIENTISTS IDENTIFY BRAIN REGIONS INVOLVED IN TRUST

WASHINGTON, DC March 31 2005 - In one of the first studies of its kind, scientists report that they have identified areas of the brain that are activated during human interactions involving trust.

The findings could have implications for the study of those with difficulty interacting with others, such as autism, or with perturbed social instincts, such as borderline personality disorder and mood disorders, says study author Read Montague of the department of neuroscience at Baylor College of Medicine in Houston.

“This study represents one of the earliest attempts to capture the brain states of more than one individual during the course of a social interaction,” says Marc Raichle of Washington University School of Medicine in St. Louis. “It marks a trend toward the study of ever more complex human behaviors such as moral reasoning and economic decision-making.”

In the study, appearing in the April 1, 2005, issue of Science, Montague and his colleagues used functional magnetic resonance imaging (fMRI) to simultaneously monitor specific regions of partners' brains as they exchanged money with each other online. In the game, one partner was the “investor” and the other the “trustee.” The investor chose how much money to send the trustee and the trustee then decided how much to return to the investor. Transactions between partners were done online, with one partner in California and the other in Texas. Forty-eight participants, divided into anonymous investor-trustee pairs, exchanged money for 10 rounds.

Each partner's “intention to trust” the other partner was signaled by a specific change in brain activity and either an increase or decrease in the repayment amount. By comparing neural responses with the repayment patterns during each exchange, the researchers found that as the game progressed, it took players, on average, 14 seconds less to repay the investor than it did when the game began. The investigators found that the participants' intention to trust brain signal shifted from a time just after the investor's decision was revealed—a reactive signal--to just before—an anticipatory signal.

Montague's group synchronized fMRI scanners over the Internet, a technique they call “hyperscanning,” to image the partners' brains. The signals they observed “have a provocative relationship to reinforcement learning models of the brain chemical dopamine and prefrontal systems,” according to Montague.

“This is important because by connecting something like trust to equations that capture dopaminergic influences on prefrontal function, we can potentially now study pathologies of trust in a testable quantitative setting,” Montague says. “We suspect that these steps forward will provide real insights into psychiatric illness.”

Montague is a member of the Society for Neuroscience, an organization of more than 36,000 basic scientists and clinicians who study the brain and nervous system. Montague can be reached at rmontague@hnl.bcm.tmc.edu.