Study: MRI sheds new light on conduct disorder
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| MRI brain scan highlights the amygdala, one of the areas of the brain that is reduced in volume in subjects with Conduct Disorder. Image Source: G.Fairchild et al, 2011. |
Conduct disorder (CD), a psychiatric condition characterized by increased aggressive and antisocial behavior, can develop in childhood or adolescence. Researchers have contended that childhood-onset CD differs from adolescence-onset, theorizing that childhood-onset represents a neurodevelopmental condition whereas adolescence-onset results from social mimicry. Recent studies had challenged this theory, showing impaired emotional learning and abnormal neural activation among patients with both types of CD.
Graeme Fairchild, PhD, of the University of Cambridge and MRC Cognition and Brain Sciences Unit in England, and colleagues designed the current study to determine whether behavioral and functional neural abnormalities are linked to similar changes in brain structure in both subtypes. Additional objectives included investigating the consequences of individual variation in psychopathic traits on brain structure and the relationships between CD symptoms and structural abnormalities, explained the researchers.
Fairchild and colleagues recruited 36 male adolescents with early-onset CD, 27 with adolescent-onset and 27 healthy adolescent males to undergo 3T MRI and complete various psychiatric inventories to measure callous-unemotional and psychopathic traits and anxiety.
The neuroimaging studies revealed no differences in total gray matter volume between groups. However, both CD subtypes showed reduced gray matter volume in the bilateral amygdala and reduced right amygdala gray matter volume relative to comparison subjects, reported the researchers. “Adolescent-onset participants also displayed reduced left amygdala volume, and reduced left amygdala volume in early-onset participants nearly reached statistical significance,” Fairchild and colleagues wrote.
However, reductions in amygdala volume were “numerically greater and statistically more robust in the adolescent onset-group,” continued the researchers.
Fairchild and colleagues noted reduced gray matter volume in the right ventral insula, left orbitofrontal cortex and left dorsomedial prefrontal cortex. Right insula volume was negatively correlated with lifetime/ever conduct disorder symptoms, continued the researchers, and “there was a positive correlation between self-reported callous-unemotional traits and volume in the caudate nucleus and ventral striatum.”
These findings reinforce earlier studies showing decreased amygdala gray matter volume and reduced temporal lobe volume in male children and adolescents with early-onset CD. However, “a key novel finding of this study is that reduced gray matter volume in limbic regions putatively involved in the pathophysiology of conduct disorder (e.g., the amygdala) is also observed in the adolescent-onset subtype. Reduced amygdala volume therefore appears to be a general characteristic of male adolescents with conduct disorder, irrespective of age of onset,” the authors noted.
The researchers suggested several avenues for future research. For example, using participants from a birth cohort or longitudinal studies may help researchers to better measure age of onset. Furthermore, the results do not establish that the structural abnormalities cause antisocial or violent behavior. Hence, “prospective studies are needed to assess whether amygdala deficits are a cause or a consequence of conduct disorder.”
Andrew J. Calder, PhD, who co-led the research, explained, “Studies such as this are tremendously important in understanding the causes of conduct disorder. Only when we are confident that we understand why the disorder develops can we apply this knowledge to the further development and evaluation of treatments.”
The study was funded jointly by the Wellcome Trust and Medical Research Council.