That feeling came even when the contribution was mandatory, like a tax. However, the 19 female student test subjects felt even better when they voluntarily made a donation, according to Ulrich Mayr, a psychology professor at the University of Oregon.

In the study, which appeared in the journal Science , Mayr and two economists gave the 19 female student 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 (specifically, the caudate nucleus and the nucleus accumbens) known for pleasure. The effect was even greater when they got to choose to give the money away.

A “Warm Glow”

According to the article, altruism sometimes is manifested as a “warm glow” associated with the act of giving. In that case, economists speculate, the act is not entirely selfless because the giver makes the donation in order to feel good (this group was referred to as “egoists”). But economists have also proposed that not all warm glows are self-interested – that some may have positive emotions wash over them just from witnessing good deeds. This is called “pure altruism,” and it may be motivating society’s biggest givers (altruists reportedly give twice as much as the egoists).

As it turns out, “That very same brain area not only tracks what is good for us, but what is good for others,” Mayr said in a phone interview with Reuters. “The fact that we find pleasurable activity in those mandatory tax-like situations strongly suggests the existence of pure altruism,” he said.

Of course, there may be a difference between giving away a fictional $100 that has been given to you for an experiment – and having $100 of your own money taken from you.