People who do something for charity without expecting anything in return could receive more of a "warm glow" than those who think they might gain from the activity, psychologists have found.
A study from the University of Sussex said altruistic generosity was more stimulating to certain parts of the brain than generosity from which people expected to get something in return.
Researchers said that knowing about the brain’s response to different kinds of giving could help charities understand the best ways to encourage people to volunteer or donate to charity, with the results suggesting they might feel more appreciated if they do something for free rather than for a bad reward.
Psychologists analysed 36 existing studies based on brain scans of 1,150 people, splitting the scans between those who had completed an act of genuine altruism, where they did not expect to receive a benefit from their actions, and strategic kindness, where they expected to gain from it.
The study found that reward areas of the brain were more active and used more oxygen when people acted with strategic kindness.
But they found that acts of altruism also activated the reward areas of the brain and some areas in the subgenual anterior cingulate cortex, which deals with emotion, reward anticipation and decision-making, were more active during altruistic generosity.
This indicated there was something unique about being altruistic with no hope of gaining something in return, the study said.
Dr Daniel Campbell-Meiklejohn, director of the social decision laboratory at the University of Sussex, who led the study, said: "What motivates us to be kind is both fascinating and important. If, for example, governments can understand why people might give when there’s nothing in it for them, then they can understand how to encourage people to volunteer, donate to charity or support others in their communities."
Jo Cutler, the PhD student who co-authored the study, said the findings raised questions about what charities could learn about what motivates their donors.
For example, said Cutler, some museums operated a membership scheme with benefits such as discounts, while others asked for small altruistic donations on arrival.
"Organisations looking for contributions should think about how they want their customers to feel," she said.
"Do they want them to feel altruistic and experience a warm glow, or do they want them to enter with a transactional mind-set?"
And allowing people to feel the "warm glow" of having done something altruistic could lead to them feeling more appreciated than if they were offered a reward, according to Cutler.
"Given that we know there are these two motivations that overlap in the brain, charities should be careful not to offer something that feels like a token gesture because this might undermine a sense of altruism," she said.
"Sending small gifts in return for monthly donations could change donors’ perceptions of their motivation from altruistic to transactional. In doing so, charities might also inadvertently replace the warm-glow feeling with a sense of having had a bad deal."