Washington DC: A new research has identified a brain marker which is associated with aggression in toddlers. Imagine a situation, where one child is teasing another. While the child teasing means it playfully, the other child views it as hostile and responds aggressively.

Behaviour like this occurs all the time in children, but why some of them react neutrally while others act aggressively is a mystery. In experiments measuring a type of brain wave in two and a half to three and a half-year-old children, who had smaller spikes in the P3 brain wave when confronted with a situational change were more aggressive than children registering larger P3 brain-wave peaks, research showed.

The results could lead to identifying at earlier stage children who are at risk of aggressive behaviour and could help stem those impulses before adolescence; an age at which research has shown aggressive behaviour is more difficult to treat. "There are all kinds of ambiguous social cues in our environment and when children aren't able to detect a change in social cues, they may be more likely to misinterpret that social cue as hostile rather than playful," said study author Isaac Petersen.

The P3 wave is part of a series of brain waves generated when an individual evaluates and responds to a change in the environment--such as changed cues in a social interaction. Previous research, primarily in adults, has shown individuals with shorter P3-wave peaks when confronted with a change in the environment tend to be more aggressive. As such, scientists believe P3 is a key indicator of aggression, as well as associated with depression and schizophrenia.

To tease out those differences in children, the researchers recruited 153 toddlers and, in individual sessions, outfitted each with a net of head sensors that measured brain-wave activity while a steady stream of tones sounded in the room. As the children watched silent cartoons on a television screen, the pitch of the tones changed, and the researchers measured the P3 brain wave accompanying each change in pitch.

The change in pitch is analogous to a change in a social interaction, in which the brain-consciously or subconsciously-reacts to a change in the environment. In this case, it was the change in pitch. Toddlers with a shorter peak in the P3 brain wave accompanying the tone change were rated by their parents as more aggressive than children with more pronounced P3 spikes. The difference in P3 peaks in aggressive and non-aggressive children "was statistically significant," Petersen says, and the effect was the same for boys and girls.

The researchers tested the same children at 30, 36, and 42 months of age to further explore the association between the P3 brain wave and aggression. The research is important because early interventions are more effective for stemming aggression.

"Evidence suggests that early interventions and preventive approaches are more effective for reducing aggression than interventions that target aggression later in childhood or in adolescence when the behavior is more ingrained and stable," Peterson added. The study appeared in the Journal of Child Psychology and Psychiatry.