The chief lesson I have learned in a long life is that the only way to make a man trustworthy is to trust him; and the surest way to make him untrustworthy is to distrust him and show your distrust. -Henry L. Stimson

From "Brain Scans Illuminate the Value of Trustworthiness," Spirituality & Health Magazine (July/August 2005):

What is the psychophysiology of trust? In other words, does everybody's brain function similarly if we establish a relationship of trust?

Sound esoteric? Not to a team of neuroscientists at Baylor College of Medicine and the California Institute of Technology who used a computerized game to study the psychophysiology of trust. Their game was based on economic exchange where trust was defined as the amount of money a sender gave to a receiver without external enforcement. What made the experiment interesting was that the pairs of people playing each game were in separate brain imaging laboratories that were 1,500 miles apart. All conventional social cues were removed from the games.

In each of the 10 rounds, one player (investor) had the option of investing any portion of $20 with the other player (trustee). The money appreciated at a rate of three times the investment, at which point the trustee had to decide how much of the tripled amount to give back. The experiment compared benevolent, malevolent, and neutral conditions in a tit-for-tat design. In the benevolent conditions, investors sent more money in response to the trustee sending less in repayment. In the malevolent condition, the investor repaid the trustee's generosity with a breach of trust. The researchers used a functional MRI to watch what was going on inside players' brains.

Scientists found that reciprocity expressed by one player strongly predicted the future trust expressed by his partner. Especially interesting was that the magnitude of the brain's response to an "intention to trust" correlated with the next play of the game, a factor that grew over the course of the series of games. In other words, the trustee grew to anticipate trust if the investor showed reciprocity in previous games.

These data, published in Science (April 1, 2005) suggest that we form mental models of other people's intentions that allow us to make predictions about their future behavior, and that these models can change over time based on our experiences: if we want to be trusted, we need to be trustworthy. These data also speak to the ways in which we are alike: we are linked in a complex system of interrelatedness, even when we are separated by thousands of miles.