On the Spectrum

Chapter 7
ABSTRACT
Objectives: In childhood, internalizing and externalizing problems are highly comorbid and this
can obscure specific brain-behavior associations. We explored brain morphological correlates
of internalizing problems in young children, accounting for externalizing comorbidity.
Methods: In 801 children at age six years, internalizing problems were defined using two
approaches: continuously (by the Child Behavior Checklist Internalizing Broadband score) and
categorically (by a latent profile analysis of syndrome scales). The latter approach empirically
defined a group of children with predominantly internalizing problems without substantial
externalizing behavior. At eight years of age, brain volumetric measures and cortical thickness
were assessed using magnetic resonance imaging. We examined the association of global
volumetric measures, cortical thickness, and subcortical regions of interest with internalizing
problems.
Results: There was no association between continuous internalizing scores and brain
morphological measures, adjusted for externalizing problems. Categorical analyses suggested
that children with predominantly internalizing problems had a smaller right amygdala than
children with no problems. In whole brain vertex-wise analyses, compared to children with
no problems, children with internalizing problems had thinner cortex in several regions of the
right hemisphere: inferior frontal, a caudal middle region of the frontal cortex, occipital, and
anterior temporal.
Conclusions: Using empirically defined classes of behavior, we showed that internalizing
problems in children aged six-to-ten years are related to thinner cortex mostly in temporal
but also in frontal regions. These findings suggest that structural differences observed in
young children with internalizing problems might be similar to the brain regions implicated in
depression or anxiety in older populations.
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