Children who engage in bullying may enjoy seeing others in pain, according to a new study, which used brain scans to study bullies' responses to violent images.

The scans, conducted by researchers from the University of Chicago, showed activity in the part of the brain associated with reward when the children were showed a video clip of one person inflicting pain on another.

Such brain activity was not evident in scans conducted on youths who do not bully others.

The findings suggest that the ability to feel empathy may be disrupted in some youths, which could lead to aggressive behaviour.

"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," study author Jean Decety, a psychology and psychiatry professor at the University of Chicago, said in a statement.

The research is published in the current edition of the journal Biological Psychology.

The small study included eight males aged 16 to 18 who were prone to starting fights, using weapons and stealing from victims.

They were compared to a control group of males who did not engage in aggressive behaviour.

The researchers showed both groups two videos: one in which someone experienced pain accidentally and another in which someone hurt another person intentionally.

The scans also showed that viewing the videos activated parts of the brain that regulate self-control parts in the non-aggressive group. These parts of the brain were not activated in the bullies.

This study is the first to use brain scans to study reaction to "situations that could otherwise provoke sympathy," Decety said.

"This work will help us better understand ways to work with juveniles inclined to aggression and violence."