The authors sought to model the unique and common variance across conduct disorder, substance misuse, and attention deficit hyperactivity disorder (ADHD) and to investigate the neurocognitive factors that relate generally or uniquely to externalizing problems in adolescence.

Personality and behavioral measures and functional imaging responses to reward sensitivity and response inhibition tasks were assessed in 1,778 European adolescents at age 14 and, using structural equation modeling, were related to the unique and common variance across externalizing problems assessed and modeled at ages 14 and 16.

Externalizing problems best fit a general-specific model made up of a specific factor representing ADHD and conduct disorder symptoms, a specific factor representing substance misuse symptoms, and a common externalizing factor representing the variance shared among all symptoms. Common variance across externalizing problems was associated with high impulsivity and delay discounting as well as low blood-oxygen-level-dependent (BOLD) response in the substantia nigra and subthalamic nucleus but high BOLD response in the presupplementary motor area and precentral gyrus during successful inhibition. Unique variance for ADHD/conduct disorder was associated with impulsivity, poor response inhibition, and high delay discounting, as well as low BOLD response in frontal brain areas bilaterally during failed inhibition. In contrast, unique variance for substance misuse was associated with high sensation seeking and delay discounting, as well as differential brain response to reward anticipation: high BOLD response in the left orbitofrontal cortex but low BOLD response in the left inferior frontal gyrus.

Personality, behavioral, and fMRI findings suggest that abnormalities in response inhibition, error processing, and reward processing are differentially implicated in underlying vulnerability specific to ADHD/conduct disorder and substance misuse and general to externalizing problems.