Brain scans at the University of Chicago have shown that brain area associated with rewards was highlighted when the youth watched a video clip of someone inflicting pain on another person.
"This is the first time that fMRI scans have been used to study situations that could otherwise provoke empathy," said Jean Decety, Professor in Psychology and Psychiatry at the University of Chicago.
"This work will help us better understand ways to work with juveniles inclined to aggression and violence," Decety added.
The researchers found that some aggressive youths' natural empathetic impulse may be disrupted in ways that increase aggression.
During the study, researchers analysed eight 16- to 18-year-old boys with aggressive conduct disorder. These boys exhibited disruptive behaviour such as starting a fight, using a weapon and stealing after confronting a victim.
The participants were shown video clips in which people endured pain accidentally, such as when a heavy bowl was dropped on their hands, and intentionally, such as when a person stepped on another's foot.
The fMRI scans showed that "the aggressive youth activated the neural circuits underpinning pain processing to the same extent, and in some cases, even more so than the control participants without conduct disorder."
"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," Decety added.
The study appears in the journal Biological Psychology.