PARIS?Humans may have a selfish gene but we also experience satisfaction in sharing out the goodies, even if this means giving away some of our own, according to an unusual study released on Wednesday.
Using 3-D hospital scanners, scientists say they have found the first evidence to show that the pleasure of helping others and of helping oneself both activate the same areas of the brain.
A quartet of scientists led by John O'Doherty of California Institute of Technology (Caltech) in Pasadena, California set up experiments with 20 pairs of male volunteers while observing their brain activity with magnetic resonance imaging (MRI) machines.
The researchers looked in particular at two cerebral regions -- the ventromedial prefrontal cortex and central striatum -- that process pleasurable "rewards" such as food, money and enjoyable music.
Each pair was given $30 to start, and then drew lots to see which of the two would be given a bonus of $50. The other person received nothing extra.
In additional transactions, the scientists openly gave different sums of money to the two participants.
If the "poorer" of the two received the larger allotment, the part of his brain under observation would light up, as expected.
More surprising, though, was the reaction of the richer participant when his poorer counterpart suddenly got a chunk of cash.
"People who started out rich had a stronger reaction to other people getting money than to themselves getting money," said co-author and economist Colin Camerer, also from Caltech.
Even when the wealthier subjects said they wanted to have the additional money, the MRI readout suggested that the opposite was true.
This apparent incongruity "highlights the idea that even the basic reward structures in the human brain are not purely self-oriented," said O'Doherty.
"Our results provide direct neurobiological evidence in support of the existence of inequality-adverse social preferences in the human brain."
It is still unclear to what extent the share-and-share-alike response registered in the brain is innate or learned, the researchers acknowledge.
"We think that, for the people who start out rich, seeing another person get money reduces their guilt over having more than others," said Camerer.
The investigators admit to limitations in their work. The experiment, which took place in the United States, does not take into account differences in culture, nor did it enroll women.
The study appears in Nature, the British science journal.