LOS ANGELES, CA (Catholic Online) - Cells fire in rhesus monkeys when they gave juice away, according to the study, but not when they received it. As published in the journal Nature Neuroscience, the study may shed light on why many animals, including humans exhibit kind, unselfish behavior that doesn't directly benefit them.

The study provides a "complete picture of the neuronal activity underlying a key aspect of social cognition," neuroscientist Matthew Rushworth at Oxford wrote in an email. "It is definitely a major achievement."

This "do-gooder" impulse in animals may have evolved into the altruism we see in humans today, said study co-author Michael Platt, a neuroscientist at Duke University.

Understanding how altruism works in the brain has been trickier. When people do something unselfish such as give to charity, reward circuits that usually fire when eating chocolate or doing something pleasurable are activated, Platt says.

People feel differently between doing well for themselves and being kind to others. Researchers studied how the brain encodes unselfish, other-oriented acts separate from personal gain.

Platt and his colleagues taught rhesus monkeys to play a simple computer game where they looked at different shapes to either give themselves, a nearby neighbor monkey or no one a squirt of juice.

Monkeys almost always give themselves juice when they have the option. After teaching the monkeys the rules of the game, the researchers set up another trial where they could either give the other monkey juice or give it nothing. None of the choices led to a tasty juice squirt for the actor monkey.

The result? The monkeys consistently preferred doling out juice to other monkeys over giving nothing. Replacing the second monkey with another bottle of juice, the monkeys showed no preference for dispensing juice, showing that they were motivated by the reward to the other monkey.

Electrodes in the monkey's brain recorded the electrical firing from neurons in brain regions suspected of playing a role in altruism. It was discovered that a brain region called the orbitofrontal cortex fired when monkeys got juice squirts for themselves. "The orbitofrontal cortex seems to be all about your personal reward. It's egocentric," Platt said.

Intriguingly, however, some neurons in a region called the anterior cingulate gyrus fired when the monkey got its own juice, while others fired when monkeys gave their neighbors juice.

It's not yet known what's going on in the monkeys' brains. The results suggest that this brain region may be partly responsible for creating primitive forms of empathy.

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