That Uneasy Feeling

When being treated in an even-handed way, some, but not all, people respond similarly. Those who do can be trusted. Those who don’t, cannot. This observation is important in human relationships when choosing business partners, friends, and romantic interests. It can mean the difference between a successful or disastrous result. It also plays an important role in the financial advisor-client relationship.

Now we know more about the sometimes fragile dynamics of trust. It can be easily fractured, and when that happens, it is difficult or even impossible to repair.

Past work showed that a judgment of fairness on the part of a participant playing the “trust game” is reflected in the brain. The “trust game” is one of 3 similar games used in Neuroeconomics testing. Each is built on the previous.*

When scientists use these games to test subjects, they found the 2 parts of the brain that program rewards—the ventral striatum and orbital frontal cortex—respond to cooperation between humans. However, what has not been studied is whether a partner’s reputation for cooperative behavior learned through interactions with the other partner is influenced by this learned reputation.

K. Luan Phan and colleagues from the University of Michigan and George Mason University set out to change this. They used a “trust game” to determine whether or not participants who perceived another player as trustworthy would be influenced by this perception. The researchers used event-related functional magnetic resonance (fMRI). Event-related fMRI refers to brain blood flow responses to neural activity during specific events.

Thirty-six subjects took part in the study with an average age of 30.03 +/- 8.64 years (22 females). The participants were told that they would play with 3 different types of players characterized on their earlier recorded actions:

1. Reciprocate >50% of the time;

2. Reciprocate < 50% of the time;

3. Reciprocate about 50% of the time.

What the players did not know was that the frequency at which reciprocation would take place was actually fixed at these rates:

1. 75%

2. 25%

3. 50%

These partner types were referred to respectively as:

1. Cooperative

2. Uncooperative

3. Neutral

When the participants found their partners trustworthy, there was enhanced activation in their ventral striatum and orbital frontal cortex. This was not noted in trials in which the partner did not reciprocate. Further, the signal of reciprocity appeared selectively in response to partners who consistently returned the investment—those people who had a reputation for reciprocity. It was not found in those who did not. This is demonstrated below.

Activation in both left and right ventral striatum in response to partner reciprocation compared with partner defection following trust decisions is selective for cooperative partners (cooperative > uncooperative; *P < 0.05). From Reputation for reciprocity engages the brain reward center, Fig. 4.

This study demonstrates neurophysiologic correlates of trust and confirms what we knew intuitively all along: if we trust someone, we feel better than if we are uneasy about them.

*The first is the “ultimatum game” in which one player given money can share it anyway he wants, but can keep money only is the second player accepts his offer. A second game, the “dictator game,” is based on the “ultimatum game,” but different in that the first player can keep the money no matter what the second player decides. Lastly, in the “trust game,” there is an initial monetary gift from the partner before the other player decides what how much money to share.

Further Reading:

How Unfair Transactions Affect You