U.S. imaging research suggests that teens with a history of aggressive bullying behavior may actually enjoy seeing someone else suffering.

Researchers conducted a small study of 16-18 year olds - eight of the male participants had aggressive conduct disorder and eight had any unusual signs of aggression. The boys watched video clips of people inflicting pain. Using functional Magnetic Resonance Imaging (fMRI), Benjamin Lahey of the University of Chicago and colleagues compared the teenagers’ brain activity.

According to the findings, published in the journal Biological Psychology, boys in both groups showed some activity in the brain’s pain centers. But, in addition to this, the brains of participants with aggressive tendency also showed activity in a different area - the brain's pleasure centers. Males without a history of unusual aggression showed no such activity, researchers said.

Furthermore, the aggressive youngsters were also found to react more strongly to pain caused by mistake (such as when a heavy bowl was dropped on someone’s hands), rather than to pain caused on purpose (for instance, when an individual stepped on another’s foot).

The study’s purpose was to better understand how to work with teenagers “inclined to aggression and violence,” asserted Jean Decety, professor of psychology and psychiatry at Chicago University, who led the study.

"It is entirely possible their brains are lighting in the way they are because they experience seeing pain in others as exciting and fun and pleasurable," said Lahey, co-author of the study.