Trust and reputation are so vital to social interaction—especially when money is involved—that they may have dedicated circuitry in the brain.
The decision to trust one’s partner in an investment game correlates with activity in a part of the brain called the caudate nucleus, according to a study by P. Read Montague and colleagues at Baylor College of Medicine, Houston, and the California Institute of Technology, Pasadena. In each of 10 rounds of the game, one partner, the investor, was given $20 and sent some, all, or none to the other player, the trustee. The money appreciated, tripling in value; the trustee then decided how much to return to the investor. The researchers monitored the players’ brain activity using functional magnetic resonance imaging.
The caudate nucleus of the trustee showed a change in activity when the trustee intended to increase repayment in the next round of play. As the game progressed, this “intention to trust” signal appeared about 14 seconds sooner—even before the investor’s decision was known—suggesting that the trustee's brain was building a model of the investor's likely behavior.
The finding, published in the April 1 issue of Science, supports earlier research with animals showing the caudate nucleus to be part of the brain’s “reward” pathway. “This pathway may be involved in the more complex goals and predictions of social interaction,” says Montague. He adds that similar studies may shed light on psychiatric conditions in which people cannot accurately gauge the mental states of others, such as schizophrenia, autism, and personality disorder.