Researchers say they've used advanced scanning methods to pinpoint the region of the brain where feelings of trust arise.
Turns out those emotions are nestled in the same area as the most powerful feeling of all - love.
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Reporting in the April 1 issue of Science, the researchers used a simplified investment game to probe the workings of the human mind.
Their work involved two advanced technologies: functional magnetic resonance imaging (fMRI), which provides detailed images of blood flow that indicate brain activity; and hyperspanning, which allows fMRI studies to be performed simultaneously on two people hundreds of miles apart.
The study was led by Read Montague, director of the Baylor College of Medicine Human Neuroimaging Laboratory, in Houston, USA.
How the research was done
The researchers hooked up 48 people - half in Baylor, the other half at the California Institute of Technology in Pasadena - to the machines and let the games begin. One person in each pair was designated as the "investor" and received $20 at the start of the experiment, and was told to decide how much to give to his or her distant partner, the "trustee."
After 10 rounds of the exchanges, the amount of money appreciated to triple its original value. The person at the other end was then allowed to decide how much money to keep and how much to leave for the partner.
By measuring brain blood flow in early rounds, the researchers identified neural signals in a specific area of the brain that seemed to predict the decision to give away more money - a sign of trust. Later in the game, that response began to occur before the previous exchange was completed, a clear sign that trust was growing.
Response in the brain's base
According to the researchers, the response occurred in the caudate nucleus, which is located at the base of the brain.
The findings came as no surprise to Dr Semir Zeki, director of the Laboratory of Neurobiology at University College London. About five years ago, Zeki and his colleagues reported a study with young people that identified the caudate nucleus as a brain region that was activated when thoughts of love flooded the mind.
Even though the Baylor study used a different kind of MRI, the results were similar, Zeki said.
"Love is a primitive, basic, emotional affective state," he said. "So is trust. Trust is something that a child has for its mother or a lover has for a lover."
A hub of activity
The new report could have real medical value because the caudate nucleus is a very busy brain centre, explained Kevin Alloway, professor of neuroscience at Pennsylvania State University, whose research centres on the caudate nucleus.
"The caudate nucleus is important in central motor integration," he said. "It processes information from wide areas of the cortex. Dopamine is important in its activity, and deletion of dopamine occurs in patients with Parkinson's disease. It plays a role in cognitive function, but that role has not been identified very well."
The study has implications beyond feelings of trust, Montague said in a statement. "We hope it can be used to better understand conditions such as schizophrenia and autism."
Zeki's study suggested that love is a much more complicated matter, however. Three other brain regions also are activated when someone falls in love, the London study found - leaving a lot of work yet to be done by neuroscientists.
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