When economists and neuroscientists get together, interesting things can happen. A team of researchers from the University of Arizona -- including a neuroscientist, a psychologist, and a behavioral economist -- used functional magnetic resonance imaging (fMRI) to examine what happens to the brain when we experience guilt. In the process, they discovered one of the main drivers of human co-operation.

First, the researchers devised an economic game designed to test the theory of guilt aversion -- our desire to avoid the negative feelings of guilt. In the game, some participants were called "investors" and were asked to award a certain amount of money to other participants called "trustees." The trustees were told that the investors expected a certain amount of money back. Then, while in an fMRI machine, the trustees' brains were scanned as they decided how much money to return to the investors.

When trustees decided to honor the investors' trust and return the amount of money expected, the fMRI scans identified significant activity in regions of the brain known to be involved in guilt-motivated behavior. Different areas of the brain known to be involved in maximizing rewards showed activity when participants decided to not honor the investors' trust and return less money than expected.

What this means is that two rather distinct neural structures are at play when we're deciding whether or not to honor someone's expectations. The neural structure underlying our desire to avoid guilt activates in conjunction with a decision to co-operate.

In other words, one of the reasons we co-operate with others is to avoid feeling guilty. The main contribution of this study is to substantiate that claim with a combination of well-tested economic and neuroscientific approaches, rather than air-filled conjecture.

Another grounded takeaway from the study is that some people are inherently more guilt-sensitive than others. The researchers demonstrated this by separately testing both kinds of trustees, those that decided to return the expected amount of money and those that decided to return less. Even when many of those that decided to not return the expected amount envisioned returning even less money, their brains still didn't show much activity in the neural structure underlying guilt. Conversely, when participants that returned the expected amount were asked how they would feel if they returned less money, activity in the neural structure underlying guilt intensified.

The study also provides a final takeaway -- that feelings are integral to economic decision-making. And if it's true that some people's brains are simply more sensitive to feelings of guilt than others, it's interesting to wonder if some of us are truly not "cut out" for the hard and fast negotiations native to many kinds of businesses, while others aren't wired to function well in roles requiring greater co-operation.

We can throw that question into the debate pit for more gnoshing. In any case, this research will hopefully catalyze more cross-disciplinary approaches to figuring out why we think as we think and do as we do.