Teenage tantrums are the stuff of every parent’s nightmares. Now we may closer to explaining why some adolescents fly off the handle more than others. Brain scans show differences in the brain structures that control emotions in adolescents who flare up at the slightest provocation, and those who are more self-controlled.

Nicholas Allen at the University of Melbourne, Australia, and his colleagues studied 137 boys and girls aged between 11 and 14 and their parents. They videotaped the families while they discussed problems designed to prompt disagreement, such as negotiating bedtime or a curfew.

There was a huge variation in behaviour, with some families barely speaking to each other, and others getting on well.

Next the team scanned the children’s brains, focusing on three regions: the amygdala, which triggers impulsive reactions to emotional situations, and the anterior cingulate cortex (ACC) and orbitofrontal cortex (OFC) – pre-frontal parts of the brain involved in more thoughtful and reflective responses.

Children of both sexes who behaved more aggressively during the problem-solving tasks had bigger amygdalas, while boys who had smaller ACCs on the left side of the brain, compared with the right, stayed aggressive for longer. Also, boys with smaller OFCs on the left side were more likely to respond to a parent’s sulky behaviour with a sulk of their own.

Psychiatric problems

In the more aggressive children, “the ‘thinking’ prefrontal cortex just isn’t exerting enough control over the amygdala to regulate behaviour”, says team member Sarah Whittle.

While some girls had similar asymmetries in their pre-frontal regions, this did not seem to affect their behaviour, even if they were aggressive. This suggests that the brain mechanisms controlling emotion and behaviour in early adolescence are different for boys and girls, the team says.

Whittle adds that the brain structures observed in aggressive boys could reflect a temporary delay in the transition to a more adult brain, as the pre-frontal circuits have yet to come fully online.

But in adults, a bigger amygdala and clear asymmetries in the volume of the ACC and OFC are associated with many psychiatric disorders, including depression, anxiety and personality disorders. It is possible, the team speculates, that in some people the pre-frontal circuits never fully come online, increasing their risk of psychiatric problems.

Journal reference: Proceedings of the National Academy of Sciences (DOI: 10.1073/pnas.0709815105)

• NewScientist.com news service
• Emma Young