Getting into the spirit of giving during the holiday season may seem like a struggle, but it turns out generous people aren’t fighting the urge to screw others over, as some have suggested.

Instead, generosity – or the desire for fairness – seems automatic and arises from activation in a brain area that controls intuition and emotion.

Neuropsychologists define “prosocial” people as those who prefer to share and share alike, and “individualists” as those who are primarily concerned with maximising their own gain.

Inequality aversion

According to one theory, the difference between these two groups is that prosocial people actively suppress their selfish tendencies with the help of their prefrontal cortex. But Masahiko Haruno of Tamagawa University in Tokyo, Japan wondered if some people might instead have an automatic aversion to inequality.


Haruno, along with Christopher Frith of University College London used functional MRI to scan the brains of 25 prosocial people and 14 individualists (presorted using a standard behavioral test) while they rated their preference for a series of money distributions between themselves and a hypothetical other person. As expected, the prosocial group preferred even splits while the individualists favoured distributions where they got the most money.

Active amygdala

A less predictable finding was that the only brain region that differed in activity between the two groups was the amygdala. When presented with unfair money distributions the activity in the amygdala increased significantly in prosocial people but not in the individualists. “And the more they disliked the split, the more activity you saw in this region,” says Frith.

“The amygdala tends to respond automatically, without thought, or even without awareness,” says Frith. Combined with the fact that there was no difference in activity in the prefrontal cortex – responsible for suppressing urges – this suggested that the suppression theory might not be borne out.

To further test if the prosocial aversion to unfairness was automatic, the researchers repeated the test, this time giving the participants a memory task to complete at the same time as they rated the splits.

They found that the prosocials’ brains still reacted to the unfair distributions, even when the parts of their brain responsible for deliberative processes were taken up by other tasks, suggesting they were not suppressing selfish desires.

Knee-jerk morality

Carolyn Declerck, a neuroeconomist at the University of Antwerp, Belgium, says the results fit with her own, as yet unpublished, data showing that prosocials seem to be driven by an automatic sense of morality. “So far, all our behavioural and fMRI experiments confirm that prosocials are intrinsically motivated to cooperate,” she says.

Haruno will next try to figure out how this difference in the activity of the amygdala arises. It’s partly genetic, but also likely influenced by a person’s environment, he says, particularly the social interactions during childhood. He says it is interesting to think there might be ways to promote this activity to “realise a more prosocial society.”

Journal reference: Nature Neuroscience, DOI:10.1038/nn.2468