In Don Juan Lord Byron wrote, 'Sweet is revenge—especially to women'. But a study released on Wednesday, supported by magnetic resonance imaging, suggests that men may be the more natural avengers. In the study, when male subjects witnessed people they perceived as had guys being stroke by a mild electrical shock, their M.R.I. scans lit up in primitive brain areas associated with reward. Their brains' empathy centers remained dull. Women watching the punishment, in contrast, showed no response in centers associated with pleasure. Even though they also said they did not like the bad guys, their empathy centers still quietly glowed. The study seems to show for the first time in physical terms what many people probably assume they already know: that women are generally more empathetic than men, and that men take great pleasure in seeing revenge exacted. Men 'expressed more desire for revenge and seemed to feel satisfaction when unfair people were given what they perceived as deserved physical punishment', said Dr Tania Singer, the lead researcher, of the Welcome Department of Imaging Neuroscience at University College London. But far from condemning the male impulse for retribution, Dr. Singer said it had an important social function: 'This type of behavior. has probably been crucial in the evolution of society as the majority of people in a group are motivated to punish those who cheat on the rest'. The study is part of a growing body of research that is attempting to better understand behavior. and emotions by observing simultaneous physiological changes in the brain, a technique now attainable through imaging. 'Imaging is still in its early days but we are transitioning from a descriptive to a more mechanistic type of study', said Dr. Klaas Enno Stephan, a co-author of the paper. Dr. Singer's team was simply trying to see if the study subjects' degree of empathy correlated with how much they liked or disliked the person being punished. They had not set out to look into sex differences. To cultivate personal likes and dislikes in their 32 volunteers, they asked them to play a complex money strategy game, where both members of a pair would profit if both behaved cooperatively. The ranks of volunteers were infiltrated by actors told to play selfishly. Volunteers came quickly to 'very much like' the partners who were cooperative, while disliking those who hided rewards, Dr. Stephan said. Effectively conditioned to like and dislike their game-playing partners, the 32 subjects were placed in scanners and asked to watch the various partners receive electrical shocks. On scans, both men and women seemed to feel the pain of partners they liked. But the real surprise came during scans when the subjects viewed the partners they disliked being shocked. 'When women saw the shock, they still had an empathetic response, even though it was reduced'. Dr. Stephan said. 'The men had none at all'. Furthermore, researchers found that the brain's pleasure centers lit up in males when just punishment was meted out. The researchers cautioned that it was not clear if men and women are born with divergent responses to revenge or if their social experiences generate the responses. Dr. Singer said larger studies were needed to see if differing responses would be seen in cases involving revenge that did not involve pain. Still, she added. 'This investigation would seem to indicate there is a predominant role for men in maintaining justice and issuing punishment'. Lord Byron's words mean______.