Published online 25 February 2008 | Nature | doi:10.1038/news.2008.619

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Brain changes linked to adolescent moods

Variation in the brain correlates with normal aggressive behaviour.

Adolescents with larger amygdalas are more likely to have long and moody interactions with their mothers.Bananastock

A study of Australian adolescents has identified changes in the brain that correlate with the normal grumbling aggression and moodiness often seen in this age group.

The study finds similar patterns in the relative sizes of parts of the brain of whining adolescents as has been seen in young adults with more serious behavioural problems. But the extent to which adolescent biology will determine a child’s behaviour later in life, or how much other factors might counter this, are not yet known.

Nicholas Allen of the University of Melbourne in Australia and his colleagues looked at the parent-child interactions of 137 young people, and linked patterns in the adolescents’ behaviour to the sizes of various structures in their brains.

“Neuroimaging research is more often done on people with mental diseases or the results are correlated with performance on psychometric tests,” says Allen. “Only rarely is it used to investigate day-to-day behaviours.”

Bones of contention

The authors, who are interested in mental-health problems that develop during the teenage years, focused their attention on 11- to 13-year-olds. “There is a huge upswing in mental-health problems when young people hit 14 or 15 years old. We wanted to look at kids before this and to ask what biological as well as environmental processes contribute to those problems,” says Allen.

The team asked each child and parent pair to discuss five subjects that often lead to disagreement between them (such as what time they had to go to bed, or the matter of tidying their rooms). Then the researchers left the room, allowing the conversation to flow uninterrupted. Video cameras trained on both subjects followed every expression of discontent as the discussion continued. When the research team played back the film, they painstakingly noted the second-by-second behaviour of both parent and grumpy offspring.

Each of the younger volunteers later lay in a magnetic resonance imaging scanner, which measured the volume of three brain structures: the amygdala, the anterior cingulate cortex, and the orbitofrontal cortex.

Size matters

The scientists found that adolescents with larger amygdalas were more likely to have long and moody interactions with their mothers. This part of the brain is well known as a centre of emotional reactivity, and an enlarged amygdala has been linked to substance abuse and depression in young people.

The two other regions — the anterior cingulate and orbitofrontal cortices, both at the front of the brain — are involved in regulating behaviour. Connections between the amydgala and these areas are not usually complete until the early twenties.

“Teenagers have a mismatch going on,” Allen says. “They have a rapidly-developing amygdala but much slower development of the structures that regulate behaviour. Parents often feel reassured when they hear that.”

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Allen and his group also revealed that young men with more symmetrical right and left brain hemispheres are more likely to argue back to their parents than those with a relatively larger left half of their brains. The asymmetric case is considered normal among adult men. The results are published in Proceedings of the National Academy of Sciences1.

'Normal' teens

“This paper fills in a missing link between structural brain differences in these key regions of adolescents’ brains and behaviour in a natural situation involving conflict,” notes Michael Posner, a psychologist at the University of Oregon in Eugene.

Environmental factors, such as a teenager’s family context, obviously have a strong influence on the likelihood of a young person developing behavioural difficulties.

What is unclear is whether the social milieu of upbringing can influence how the brain develops through early adolescence, or how permanently those developmental changes affect behaviour in later life.

Allen and his team say that they may have early evidence that upbringing does affect the brain, probably through hormonal interactions. This data is too preliminary to discuss, but they plan to follow this class of grumblers for the next five years to investigate further. 

  • References

    1. Whittle, S. et al. Proc. Natl Acad. Sci. USA, 105, 3652-3657 (2008).
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