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University of Cambridge researchers performed the largest ever study to look at the brain structure of teenagers diagnosed with conduct disorder (American Journal of Psychiatry: tinyurl.com/63exz4l).
Graeme Fairchild and colleagues at the University of Cambridge scanned the brains of 65 male teenagers (average age 18 years) with a conduct disorder diagnosis and 27 male, age-matched teenage controls. The results, published online in March, found reduced amygdala volume in teenagers with conduct disorder, but no differences in brain structure according to age of onset of the disorder.
The amygdala result matches findings using functional brain scans and the presentation of fearful faces (see 'Kids behaving badly' report), but the lack of correlations between brain structure and age of onset undermines a popular theory in the field (the developmental taxonomic theory), which proposes the condition consists of two subtypes - an early-onset version associated with neural abnormalities, and a later-onset version triggered by peer influence.
The study also uncovered a correlation between insula volume and severity of conduct disorder. Given previous research on the function of the insula, this anomaly is possibly associated with a diminished ability to process other people's emotions and an insensitivity to punishment. Reduced volume was also observed in the dorsomedial prefrontal cortex, involved in executive control and reasoning about other people's mental states.
In contrast to previous research, no correlation was observed between amygdala volume and callous/unemotional traits. But there was a positive correlation between these traits and increased volume of caudate nucleus and ventral striatum - perhaps reflecting a greater sensitivity to reward in these teenagers.
'Our results...support the proposal that both forms of conduct disorder [early- and later-onset] may stem from dysfunction in neural circuits involved in emotion processing, contrary to the developmental taxonomic theory,' the researchers said.
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