| Externalizing behavior describes a broad spectrum of conduct, including aggression, impulsivity, and hyperactivity. Research on the neural mechanisms contributing to individual variance in externalizing behavior has invoked regions involved in emotion and decision making, including the ventromedial prefrontal cortex (vmPFC), anterior cingulate cortex (ACC), and amygdala. Variation in the development of these regions may influence one's propensity for externalizing problems and, by extension, one's vulnerability for disorders such as conduct disorder and attention deficithyperactivity disorder. In a large sample of children and adolescents the trajectory of development in these regions is compared in boys and girls. Decreased volume of these regions in association with higher externalizing behavior is hypothesized along with sex differences in the relationship, such that in boys and girls the brain-behavior relationship would be strongest on the right and left side, respectively. 117 volunteers (61 boys, 56 girls) in the age range of 7 to 17 participated. Externalizing behavior was measured using the Pediatric Behavior Scale, a parent- and teacher-reported rating scale. Structural MRI and a combination of automated and manual segmentation techniques produced morphometric measures. A summary of the main findings are as follows: Robust sex differences were detected in comparing volumetric measures, with boys having larger raw volume for all regions except the ACC. After correcting for global size differences the ACC was proportionally larger in women. Qualitative differences in the trajectory of vmPFC development were present such that in girls there was a reduction in volume with age that was not observed in boys. There was a relationship of decreased right vmPFC and right ACC volume in association with increased externalizing behavior in boys, with medial vmPFC most highly correlated with impulsivity and hyperactivity and ACC with antisocial behavior. In girls there was no evidence of a significant brain-behavior relationship, though this may have been the result of lower variance in the behaviors of interest. Taken together, these results are consistent with the hypothesis that right vmPFC and ACC volume may act as neuroanatomical correlates of externalizing behavior in boys. |
