Dissociated functional brain abnormalities of inhibition in boys with pure conduct disorder and in boys with pure attention deficit hyperactivity disorder

Objective: Inhibitory dysfunction may be a transdiagnostic etiopathophysiology of disruptive behavior disorders. Functional magnetic resonance imaging (fMRI) of inhibitory control has only been investigated in patients with attention deficit hyperactivity disorder (ADHD), including comorbidity with conduct disorder, showing frontal-striatal dysfunction. This study investigates differences and commonalities in functional neural networks mediating inhibitory control between medication-naive adolescents with pure conduct disorder and those with pure ADHD to identify biological markers that distinguish these clinically overlapping disorders. Method: Event-related fMRI was used to compare brain activation of 13 boys with noncomorbid conduct disorder, 20 with noncomorbid ADHD, and 20 normal boys during an individually adjusted tracking stop task that measures the neural substrates of inhibition and stopping failure. Results: During successful inhibition, only patients with ADHD showed reduced activation in the left dorsolateral prefrontal cortex in relation to comparison subjects and patients with conduct disorder. During inhibition failures compared to go responses, both patient groups shared underactivation in the posterior cingulate gyrus in relation to comparison subjects. Patients with conduct disorder showed reduced activation in bilateral temporal-parietal regions compared to the other groups, which did not differ in this measure. Conclusions: Patients with pure ADHD or pure conduct disorder show qualitative differences in their brain abnormality patterns during inhibitory control. Inhibition-mediating prefrontal regions appear to be specifically reduced in ADHD, whereas posterior temporal-parietal, performance monitoring networks are specifically dysfunctional in conduct disorder. The findings provide pioneering evidence that distinct neurobiological abnormalities may be underlying the overlapping behavioral phenotype of the two disruptive disorders.