Internalizing versus externalizing comorbidity: neural circuit hypothesis.

The aim of the present study was to review and update historical controversies in relation to the limbic system in light of advances in the neuroanatmy and neurobiology of cortico-striatal-thalamic-cortical (CSTC) neural circuits. It is hypothesized that observed comorbidities between internalizing and externalizing childhood syndromes may be better understood in terms of excess communication between subcortical brain circuits. A neuroanatomical understanding of reciprocal and non-reciprocal connections between modular circuits provides a basis for understanding previously puzzling aspects of internalizing, externalizing comorbidity. Function depends on the degree of cooperative integration of goal orientation, Pavlovian stimulus response, and operant processing in cortical-subcortical circuits, and interventions may be targeted at any of these functions.