That warm, fuzzy feeling you get when you're being generous or charitable happens when the brain areas involved in generosity and in happiness synchronise.
But fundamentally, being generous means spending resources – be they time, energy or money – on another person that you could be spending on yourself. According to conventional economic theory, this is very surprising: prioritising others over yourself might leave you with fewer resources.
Now neuroscientists have pinpointed how generosity is linked to happiness on a neural level, in a study in the journal Nature Communications.
In a study of 50 people, half were given the task of thinking about how they'd like to spend 100 Swiss Francs (£80) on themselves over the next four weeks. The other half were told to think about how they'd like to spend it on someone else – for example, a partner, friend or relative. They took a test to measure their subjective level of happiness before and after the experiment.
The people who were told to spend the money on others had a bigger mood boost than the group who had planned more treats for themselves.
Immediately after this test, the participants took part in another one. They were put in an fMRI scanner and their brain activity was measured while they were asked questions about how to distribute money between themselves and someone else they knew.
They were given the chance to accept offers such as giving their chosen person a present of 15 Swiss Francs even if it cost them 20 Francs. The people who had been in the 'generous' group in the first experiment tended to be more generous in this activity.
The decisions people made in the experiment weren't just hypothetical, they had real consequences.
"The people were told that one of those options would be randomly chosen and then realised. So, for example they would have to pay 20 Francs and we would send other person the 15 Francs with a letter explaining why they were receiving it," study author Soyoung Park of the University of Lübeck, Germany, told IBTimes UK.
The scans revealed the brain areas that were most active during the acts of generosity. The area associated with generosity – the temporo-parietal junction – and an area associated with happiness – the ventral striatum – both lit up particularly strongly during the fMRI scans. In addition, the activity of the two regions synchronised.
People tend not to realise how happy generous giving will make them, the researchers conclude.
"In everyday life, people underestimate the link between generosity and happiness and therefore overlook the benefits of prosocial spending. When asked, they respond that they assume there would be a greater increase in happiness after spending money on themselves and after spending greater amounts of money," the authors write in the study.
"Our study provides behavioural and neural evidence that supports the link between generosity and happiness. Our results suggest that, for a person to achieve happiness from generous behaviour, the brain regions involved in empathy and social cognition need to overwrite selfish motives in reward-related brain regions. These findings have important implications not only for neuroscience but also for education, politics, economics and health."