A University College London brain imaging study suggests men gain greater satisfaction than women when witnessing retribution.

The study -- conducted at the Wellcome Trust biomedical research charity at UCL -- involved 32 male and female volunteers plus four "confederates" who were actually actors, but that fact was kept from the rest of the group.

In the first part of the experiment, volunteers played a monetary investment game, giving cash to the actors who had to then decide how much to give back. One actor behaved fairly, while the "unfair" actor returned very little, if any money at all.

The volunteers were then placed in a magnetic resonance imaging brain scanner, and researchers measured empathic responses as the actors received a mild electric shock. When the "fair" actor received the shock both female and male volunteers showed empathy activation in pain related areas of the brain.

When the unfair actor received a shock the women showed empathy. However, brain images of the men showed no increased activity, but did reveal a surge in the nucleus accumbens, the "reward" region of the brain.

The study appears in the journal Nature.

Copyright 2006 by United Press International