In this study, Montague and his colleagues, including the paper’s first author, Brooks King-Casas, measured, via functional magnetic resonance imaging, the blood flow in the area of the brain where this intention-to-trust mechanism occurs. Blood flow to this area was measured by functional magnetic resonance imaging machines in each site of the experiment. This allowed the researchers to measure how and when trust decisions were made. The measurements were done on 48 pairs of subjects involved in the rounds.

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.

The technique holds promise for understanding diseases such as autism – in which the ability to form models of the actions of other people is impaired. Or it might help in the understanding of maladies such as schizophrenia.

From a Baylor press release.