Sex split: only male enjoys suffering of foe

Tania Singer and Klaas Emmo Stephan, both researchers at University College London, had 16 men and 16 women play a monetary game with people they didn't know were actors. One actor played fairly, the other cheated.

Then, while study subjects were in a brain-imaging device, they watched as either of the two actors received a painful jolt of electricity on their hand - the equivalent of a bee sting.

How the observer's brain responded told the whole story of how they felt about the person they believed was either fair or was a cheater.

When a likable person was shocked, the observer's brain reacted as if he, too, felt pain.

The brain has specific pain circuits activated by a person's emotional experience. Many of the same brain regions were activated in the subject - even though they were not shocked themselves. It's a neural sign of empathy.

But these brains didn't exhibit any signs of empathy for the cheater. However, it was here that the gender differences emerged, Ms Singer said.

When watching someone they believed had cheated them receive a painful shock, all of the males showed brain activity in a region associated with pleasure and reward.

Clearly, the men relished the punishment of a foe. Female brain scans did not find this response, even toward the actor who cheated.

The study appeared yesterday in the journal Nature.

"Empathy can be shaped by the perceived fairness of other people," Ms Singer said.

The researcher said she suspects that her findings say something about the stability of a co-operative society.

If someone deviates from a co-operative role, another may feel cheated and desire to punish that person to reinforce society's norms.

Ms Singer speculates that men traditionally have had a prominent role in maintaining justice in society - and they may in fact be biologically primed to do so.

Jamie Talan, 'The Irish Times', 20 January 2006