Researchers have created a computational model capable of predicting when a person is going to act generously or not, offering a new perspective on how people come to make altruistic choices.

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The study, led by researchers from Caltech, “generates several novel insights into the nature of altruism.”

“We take a very simple model of choice that’s been developed for predicting perceptual decisions – like whether a dot is moving left or right – and adapt it to capture generosity,” says lead author Cendri Hutcherson, also a director of the Decision Neuroscience Lab at the University of Toronto in Canada.

“With this simple model, we are able to explain a huge host of previously confusing patterns about how people make altruistic choices.”

The question of why people act altruistically, helping others at personal cost, is one that has concerned thinkers throughout history, from Aristotle to Nietzsche to Levinas. Some people believe that humans find generosity naturally rewarding while others find that humans are innately selfish, only acting generously as an exercise in self-control.

According to the computation model developed by researchers at the California Institute of Technology (Caltech), neither of these positions is wholly accurate. Instead, the researchers posit that both acting generously and selfishly can be natural, with decisions depending on the individual and the context.

“We find that what matters is not whether you can exert self-control, but simply how strongly you consider others’ needs relative to your own,” Hutcherson explains. “If you consider the other person’s needs more, being generous feels easy. If you consider yourself more, generosity requires a lot of effort.”

The researchers constructed their computational model using the brain scans of 51 male volunteers participating in a game where they had to make choices between real monetary prizes for themselves or an anonymous partner.

Volunteers were asked if they would sacrifice different amounts of their money to enable a stranger to get a significantly larger amount – for example, sacrificing $25 of their money so that their partner would receive an extra $100. Each participant had to make 180 of these decisions and their brains were scanned while they did so.

The researchers believe that the brain scans indicate specific areas of the brain are linked with people’s own interests and the interests of others. Self-orientated decisions were associated with activity in an area linked to reward processing while decisions focused on others were associated with activity in a region of the brain linked with empathy.

Hutcherson – who worked on the study as a postdoctoral fellow at Caltech – believes the model contributes to the debate whether acting generously is innately rewarding or not:

Researchers have observed that if you act generously then you see greater activity in areas of the brain that represent reward value, and so have concluded that generosity is an inherently rewarding act – but our model actually suggests that you can get that activity just because of the way these regions construct a decision.”

“You would see more activation in reward areas simply because the decision is complex and so requires more processing to make,” she adds.

Most of the participants made selfish decisions, although on occasion even the greediest volunteers acted generously. The researchers believe that such decisions were actually mistakes rather than being acts of self-control – momentary lapses in judgment where the individual miscalculated the benefit to themselves of their actions.

The model indicates that generous choices are made more slowly if the relative weight placed on the individual is higher, but more quickly if weights on the payoffs for other people are higher.

Hutcherson says their results reveal people are happier when mistaken acts of generosity do not occur. “But if we can increase people’s focus on the thoughts and experiences of others, we can decrease those mistakes while increasing charitable giving and making altruism feel a lot easier,” she concludes.

The study is published in Neuron and was funded by the National Science Foundation, the Gordon and Betty Moore Foundation, and the Lipper Foundation.