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Economists have literally looked inside the heads of people who give money to a good cause and found that the warm glow of true altruism really does exist - at least in women.
People who volunteer to donate to charity feel much better about giving money than they do when paying their taxes, according to a study which used a brain scanner to analyse the biological basis of spending money.
Two economists and a cognitive psychologist studied how the brain reacted when women were given money to spend - or not to spend - on a food aid project and on government taxes.
As the volunteers watched the financial transactions take place, deep-seated parts of the brain were stimulated.
Nerve cells in the caudate nucleus and the nucleus accumbens normally fire when someone eats a favourite food. This time they became excited when the money went to a food charity - but less so when it went to a tax office.
"The surprising element for us was that in a situation in which your money is simply given to others - where you do not have a free choice - you still get reward-centre activity," said Professor Ulrich Mayr, a psychologist at the University of Oregon.
"I don't think that most economists would have suspected that. It reinforces the idea that there is true altruism.
"I've heard people claim that they don't mind paying taxes, if it's for a good cause - and here we showed that you can actually see this going on inside the brain, and even measure it," he said.
In the study, published in the journal Science, 19 women were each given $100 to "spend" on computer transactions while they were scanned by a functional magnetic resonance imager. None was aware of what the others were doing.
Professor William Harbaugh, an economist at Oregon and a member of the US National Bureau of Economic Research, said the study provided an unprecedented opportunity to see what people really thought about giving money to different causes.
"We actually see people getting rewards as they give up money. Neural firing in this fundamental, primitive part of the brain is larger when your money goes to a non-profit charity to help other people. On top of that, people experience more brain activation when they give voluntarily."
But the researchers warned that society could not rely on people to give voluntarily because some people were prepared to take a "free-ride" on other's charitable donations.
" Professor Mayr said people were, to varying degrees, pure altruists. "On top of that, they like the warm glow they get from charitable giving. Until now we couldn't trace that."
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