Revenge may indeed be a dish best served cold, but it would also appear to be a dish best served by men:

In a clever two-phase experiment, the researchers recruited 32 male and female volunteers, as well as four others who were undercover actors hired to play the role of volunteers.

In the first part of the experiment, the group played a game of mutual investment in which they had to give money to one of their number.

The recipient could decide for himself how much to give back from the profits.

He or she could hand back up to triple the investment, but at little reward to himself; or he could hand back little or nothing, thus maximising his own gains but at the investor’s cost.

One actor was cast in a generous role, always giving lots of money back to his partners, while another actor was cast as a meany, giving back very little and sometimes nothing at all.

Body language by the volunteers, confirmed later in questionnaires, confirmed that they did not like the actors who had cheated on them. “Fair” players, in contrast, were rated as more agreeable, more likeable and, remarkably, more attractive.

In the second phase, the same volunteers were each placed in a magnetic resonance imaging scanner, a device which shows blood flows within the brain.

The volunteer was then given a demonstration of a mild shock — the equivalent of short bee-sting — and then watched as the actors, standing next to the scanner, got the same painful treatment.

When a “fair” actor received a shock, the scanner showed empathy among all the volunteers.

In males and females alike, the images showed activation of the anterior insula/fronto-insular cortex (AI/FI) and anterior cingulate cortex (ACC). Previous research has showed that these parts of the brain cause the feeling of distress when one sees someone else in pain.

When an “unfair” actor got a shock, the AI/FI and ACC lit up again among most female volunteers.

Amongst the men, however, these empathic areas showed no increase in activity.