When we play nice with others, perhaps collaborating with colleagues on a big presentation at work, what’s the motivation? Part of it may be because it actually feels good to help out and get along with others. Research has actually backed this up: Brains scans show that reward centers of the brain "light up" when people are in the act of cooperating.

But there’s another side to cooperation, one that is fueled by the desire to avoid negative feelings, rather than chase the good ones.

The team found that areas of the brain associated with guilt were activated when people made decisions. And different areas lit up when people were chose to benefit the other person or to benefit themselves.

The research team at the University of Arizona wanted to see what’s happening in the brain during acts of cooperating – or not – with others. They had the participants play a game involving investments, and trust. The participants were given money by "investors" and had to decide how much to give back, taking their beliefs about the investors’ expectations into account.

Researcher Martin Dufwenberg, Professor in the Department of Economics at the University of Arizona explains: "I would feel guilt if I give you less than I believe that you expect that you will get. Then we measure expectations in the experimental situation. The theory predicts when people will experience guilt. Then we see how that correlates with brain activity."

The team found that areas of the brain associated with guilt were activated when people made decisions. And different areas lit up when people were chose to benefit the other person or to benefit themselves. In fact, people who said they would have experienced more guilt if they had returned less money had more activity in a brain area associated with guilt; on the other hand, people who said they wouldn’t have experienced any additional guilt had less activity in the same brain area. As study author PhD candidate Luke Chang puts it, "there is a whole other world of motivation to do good because you don't want to feel bad. That is the idea behind guilt aversion."

The authors conclude that, "trust and cooperation may depend on avoidance of a predicted negative affective state": in other words, people may cooperate to avoid feeling guilty later. This may seem like a selfish motivation for being nice to others, since it’s driven by the desire to avoid feelings of guilt. On the other hand, guilt may work to tell us that something is amiss – perhaps that we’ve wronged another person – so to avoid this red flag may be so bad after all. More research will be needed to understand exactly how our emotions create our motivations.

The study was led by researchers at the University of Arizona and published in the May 12, 2011 issue of Neuron.