Scientists in the US examined brain scans of bullies and non bullies and found them to differ in their response to scenes of pain.  The researchers found the area associated with reward was stimulated when violent teenagers were shown pictures of people inflicting pain on others which is contrary to current thinking that aggressive teens lack the ability to empathize with people in pain and that their violent behavior could be innate as well as learnt.

Professor Jean Decety, who holds post in the Departments of Psychology and Psychiatry at the University of Chicago, and other colleagues from the University conducted the research on eight boys 16 to 18 years old all of whom had aggressive conduct disorder with boys of a similar age who had no signs of aggression.

Both the groups were tested with a brain scan using a type of brain scan called fMRI (functional magnetic resonance imaging), while looking at video clips of people who endured pain accidentally, like a heavy bowl accidentally falling on their hands, and intentionally like when a person stepped on another’s foot.

The scans of the aggressive youth’s brains showed that an area linked with rewards was highlighted when the youth saw video clips of a person inflicting pain on another. The youth who did not exhibit aggressive symptoms did not have the same response.

“This is the first time that fMRI scans have been used to study situations that could otherwise provoke empathy,” said Decety.

“This work will help us better understand ways to work with juveniles inclined to aggression and violence. Aggressive adolescents showed a specific and very strong activation of the amygdala and ventral striatum (an area that responds to feeling rewarded) when watching pain inflicted on others, which suggested that they enjoyed watching pain,” he added.

Benjamin Lahey, Professor of Epidemiology and Psychiatry at the University of Chicago, who co-authored the paper said, “This suggests that children with aggressive conduct disorder who bully may not be emotionally unresponsive to pain in their victims as we thought, but may actually find seeing victims in pain to be exciting and enjoyable.”

Decety said that the brain scans of the CD group, the boys with a history of aggressive and bullying behavior, showed their reward centers lit up when they watched pain being inflicted on others, suggesting that they enjoyed watching pain. "These preliminary findings suggest that youth with aggressive CD exhibit an atypical pattern of neural response to viewing others in pain that should be explored in further studies."