We don’t need to learn the pleasure of receiving; the brain's reward system evolved eons ago to drive us to eat, drink and copulate. But the joy of giving is a learned response, and it ties reward into the brain's trust and love circuitry.
Grafman's team had volunteers play a computer game in which they would sometimes receive an imaginary monetary reward and other times have the opportunity to donate it to a variety of charities. Under the scanner, when people received money, the parts of the brain that release dopamine lit up. Dopamine is the brain's own opiate, the neurochemical that makes sex, food and drugs so rewarding.
Giving also activated parts of the prefrontal cortex, the "executive brain," the part that, in humans, makes decisions that may override our basic instincts. According to Grafman, this shows that taking pleasure in giving is a learned response. (just as the release of oxytocin in response to intimacy with others is learned after birth). From the article in Science Central,
Grafman points out that while kids get excited about receiving gifts, their parents prefer the Santa Claus role. "I think if you have young children you can see that they're much more excited when they're receiving something and they don't like giving something up to somebody else. So clearly, donating is a much more learned behavior than simply taking or receiving from others ... in some sense, you have to experience donation, you have to be persuaded to donate in the beginning. But once you do donate you'll come back and give more because you'll realize what a pleasurable sensation it was to donate."