CHICAGO - Knowing your money is going to a good cause can activate some of the same pleasure centers in your brain as food and sex, U.S. researchers said on Thursday.

People who participated in a study got a charge knowing that their money went to a charity -- even when the contribution was mandatory, like a tax. They felt even better when they voluntarily made a donation, researchers found.

Ulrich Mayr, a psychology professor at the University of Oregon, said the research sheds light on the nature of altruism and could help people feel better about being taxed.

"It shows that in an ideal world you could have a tax situation where you could be a satisfied taxpayer," said Mayr, whose study appeared in the journal Science.

In the study, Mayr and two economists gave 19 women volunteers $100 each and then tracked their brain activity in a functional magnetic resonance imaging scanner.

The women were shown their money automatically being transferred from their account to a local food bank.

When the money reached the food bank account, it activated portions of the brain -- the caudate nucleus and the nucleus accumbens -- known for pleasure. The effect was even greater when the people got to choose to give the money away.

"What is interesting is that these pleasure areas are for really basic needs, like food, sex, sweets, shelter and social connection," Ulrich said in a telephone interview. "It's the area that tells the brain what is good for us."

As it turns out, "That very same brain area not only tracks what is good for us, but what is good for others," he said.

He and colleagues were hoping to find out whether there was something in the act of giving itself -- and not just the social and egotistical reward of being a philanthropist -- that offers satisfaction.

"The fact that we find pleasurable activity in those mandatory tax-like situations strongly suggests the existence of pure altruism," he said.

Of course, simulating a tax is quite different from paying taxes to a government with policies you may or may not support, he noted.

"What it shows is that, in principle, we are capable of feeling good about doing our share," he said.

"The question is, 'Why is it that so often we feel bad about filling out our taxes?' Our study shows it is worth looking for an answer."