The new hyperscanning MRI technique holds promise for understanding certain types of mental illness, such as autism, in which the ability to form models of the actions of other people is impaired. Or it might aid the study of other psychiatric disorders, such as schizophrenia.

Dr. P. Read Montague Jr. and colleagues at the Baylor College of Medicine Human Neuroimaging Laboratory and California Institute of Technology in Pasadena, California, describe where and when trust is formed between two anonymous people, more than 1,500 miles apart, interacting in a prescribed negotiation game.

May Assist Autism, Schizophrenia Research

They found that as the negotiations progressed, the trust response occurred earlier and earlier in the subjects' interchanges. A decision about trust occurred even before the latest interaction was completed.

A breakthrough technique -- hyperscan-fMRI (functional magnetic resonance imaging), or hyperscanning -- allowed Montague, a professor of neuroscience at BCM, and his colleagues to synchronize the scanning of two interacting brains.

Eventually, hyperscanning might give insights into all kinds of negotiations, from the economic to the social to the political -- even across geographical boundaries.

However, it also holds promise for understanding certain types of mental illness, such as autism, in which the ability to form models of the actions of other people is impaired. Or it might aid the study of other psychiatric disorders, such as schizophrenia, the researchers suggest.

Hyperscanning Technique

Without hyperscanning, the researchers could not have looked at both brains at once, a factor that made the study possible. In fact, Montague and members of his team developed the software for hyperscanning and have made it freely available to the research community.

The research team, including the paper's first author, Brooks King-Casas, measured the blood flow in the area of the brain where the intention-to-trust mechanism occurs via functional magnetic resonance imaging machines used at each site of the experiment.

This procedure allowed the scientists to measure how and when trust decisions were made. The measurements were taken on 48 pairs of subjects involved in the rounds.

Experience Speeds Trust Response

Each subject was instructed separately in the rules of the game. One -- the investor -- received $20 during the first of the 10 rounds of the game. That person decided how much money to give the other subject. That sum was then tripled.

The other subject, 1,500 miles away, decided how much of the money he or she kept and how much he or she left for the other subject. Each interaction of that type completed a round.

"What we map on are the changes in blood flow," said Montague. "Those tell us the amount of trust and trustworthiness, the degree of betrayal and benevolence."

In early rounds, Montague and his colleagues were able to identify a physical response in the brain of the trustee that correlated with the intention to increase their trust or investment on the next move.

By later rounds, the timing of that response changed so that his or her intention to trust occurred before the completion of the previous round.