Researchers at Baylor College of Medicine (BCM) have mapped not only where trust forms in the brain but have also uncovered clues as to how humans represent themselves and others as physical responses in their brains. Results are reported in this week's issue of the journal Science.
The study, led by Dr. Read Montague, professor of neuroscience at BCM and director of its Brown Human Neuroimaging Laboratory, used functional magnetic resonance imaging (fMRI) to monitor brain activity in pairs of subjects during a social exchange game. The study made use of a new approach to studying social interactions, called hyperscanning, where two interacting brains are monitored simultaneously. The work revealed the existence of a new kind of map in the brain -- a "social agency map" that keeps track of "who" is responsible for an outcome during a social exchange between two interacting partners. The group found the map in an area of the brain called the cingulate cortex, which is known to be involved in bonding and social interactions.
Like the brain's sensory mechanisms that interpret and respond to sights and sounds, the process of building trust involves constructing models of other people and using those models as foundations for making decisions. Social decisions are among the most important kind for humans. "This is a region of the brain that is overdeveloped in humans and other social species and is a region you can monitor in social exchanges between people with either functional or dysfunctional social capacities," said Montague. "A degree of credit is something your brain has to assign before it ever starts assigning social agency. Your self-image, the degree to which you can carve yourself off from the rest of the world, is critical before you ever become a social creature."
Previous results from the same study, reported last year in Science, showed where and when trust forms in the brains of two anonymous people interacting via hyperscanning. Dr. Brooks King-Casas, first author in the previous paper, says this work will improve understanding of a variety of psychiatric and developmental disorders that are primarily social in nature. He plans to use the same tasks in clinical populations where the capacity to model or trust others is broken or performing pathologically.
"We've had a tough time understanding illnesses like borderline personality disorder on a biological level because we're only beginning to understand basic neural mechanisms underlying cooperation," said King-Casas. "However, with hyperscanning, we're able study brain activity between two people as interpersonal relationships develop and break down."
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