Aggression in some teenage boys may be linked to overly large amygdalas, a region in the brain involved in emotion and other functions, a study by scientists in Australia and the United States has found.

In an article in the Proceedings of the National Academy of Science, they report that these boys may also be unable to control their emotions because other parts of the brain that normally control strong emotions don't mature till the early 20s.

"It is important for parents to bear in mind that while their teenage child looks like an adult and does very complicated work at school, parts of their brain are still developing really until the 20s," Nicholas Allen at the University of Melbourne's psychology department said.

"Those parts of the brain that help the child control his own emotions and behaviour... it's important to realize that these parts of the brain are still developing for these young people."

In the study, 137 12-year-old boys and their parents were asked to discuss sensitive issues, such as homework, bed times and internet times; and the boys had their brains scanned later.

"Boys who had large amygdalas spent more time behaving in an aggressive way," Allen said, referring to a part of the brain located deep within the medial temporal lobes that is believed to be involved with emotional responses, including arousal and fear.

These boys also appeared to have small prefrontal cortexes, a region of the brain that has to do with regulating emotions.

"What we observed here was that these parts of the brain, when they are less developed in boys, it seems that they are associated with these kinds of behaviour, more aggressive and more negative emotions when they interact with their parents."

Reuters