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Defining trust: New technology captures mental process

by Ruth SoRelle, MPH

Brooks King-Casas, left, P. Read Montague, Jr., and Damon Tomlin

Your mother always told you trust is a two-way street.

Now researchers at Baylor College of Medicine have defined a roadmap of trust by studying the interaction of two brains. Accomplishing this task took new technology, the magic of the Internet and interactions 1,500 miles apart.

In a report in this week's issue of the journal Science, P. Read Montague Jr., PhD, and colleagues at the BCM Human Neuroimaging Laboratory and California Institute of Technology in Pasadena, Calif., describe not only where trust decisions occur in the brain, but also trace when those decisions are made as a relationship develops between two anonymous people interacting via functional magnetic resonance imaging in machines more than 1,500 miles apart. They found that as the interaction continues, the trust response occurs earlier and earlier in the subjects' interchanges. In the final interaction, a decision about trust occurs even before the latest interaction is completed.

Long-range implications

"This study has implications beyond economics or even interactions of this kind," said Montague, a professor of neuroscience and director of the Human Neuroimaging Lab at BCM. "We hope it can be used to better understand conditions such as schizophrenia and autism."

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

How it works

Functional magnetic resonance imaging or fMRI is similar to regular MRI in that it uses a strong magnet and radio waves to produce very clear images of tissues in the body. A person lies on a table with the part of his body to be imaged surrounded by a large magnet. When the magnet is active, it aligns some of atoms in the patient's organ (such as the brain). Then a pulse of radio waves knocks these atoms out of alignment. As they realign themselves, they emit radio waves, which are sent to a computer. From these waves, the computer assembles a picture of the organ of interest.

fMRI takes advantage of the fact that when part of the brain becomes active, small blood vessels in that area dilate, causing more blood to rush in. As the freshly oxygenated blood rushes in, it displaces blood without oxygen and causes a small change in the magnetic field. (Blood contains iron atoms in hemoglobin. These atoms distort the magnetic field around them.) The MRI can detect the change in the magnetic field, locating the areas of the brain that are active.

Montague and his colleagues combined fMRI with hyperscanning. Hyperscanning allows many subjects, each in a separate MRI scanner, to interact with one another while their brains are being scanned simultaneously. This allows researchers to look at how the brain reacts to social situations. Montague has been developing and refining the technique at BCM. His group has written Hyperscan software that was recently released freely to the research community. The software makes it possible for one scientist to control multiple scanners via the Internet. In many instances, the scanners are thousands of miles apart.

Mapping changes

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.

Others who participated in the research include Damon Tomlin of BCM and Drs. Cedric Anen, Colin F. Camerer and Steven R. Quartz of CalTech.

(This work was supported by the Center for Theoretical Neuroscience, the National Institute of Drug Abuse, The Kane Family Foundation, The David and Lucile Packard Foundation and The Gordon and Betty Moore Foundation.)

Previous news items on Montague and the Human Neuroimaging Laboratory include Images of a Social Brain and Neuroscience breaks down soft drink 'battle' inside brain.

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