Objective: Among children, attention deficit hyperactivity disorder (ADHD) and conduct disorder are often comorbid and overlap clinically. Neuropsychological evidence suggests that children with conduct disorder demonstrate more prominent motivational problems and children with ADHD demonstrate more prominent attention deficits relative to healthy comparison subjects. The purpose of the present study was to investigate disorder-specific abnormalities in the neurobiological correlates of motivation and sustained attention in children and adolescents with pure conduct disorder and children and adolescents with pure ADHD.
Method: Participants were male pediatric patients, ages 9-16 years, with noncomorbid conduct disorder (N=14) and noncomorbid ADHD, combined hyperactive-inattentive subtype (N=18), as well as age- and IQ-matched healthy comparison subjects (N=16). Both patient groups were medication naive. Event-related functional magnetic resonance imaging (fMRI) was used to compare brain activation during a rewarded continuous performance task that measured sustained attention as well as the effects of reward on performance.
Results: During the sustained attention condition, patients with noncomorbid ADHD showed significantly reduced activation in the bilateral ventrolateral prefrontal cortex and increased activation in the cerebellum relative to patients with noncomorbid conduct disorder and healthy comparison subjects. Patients with noncomorbid conduct disorder showed decreased activation in paralimbic regions of the insula, hippocampus, and anterior cingulate as well as the cerebellum relative to patients with noncomorbid ADHD and healthy comparison subjects. However, during the reward condition, patients with noncomorbid conduct disorder showed disorder-specific underactivation in the right orbitofrontal cortex, while patients with noncomorbid ADHD showed disorder-specific dysfunction in the posterior cingulate gyrus.
Conclusions: The findings revealed a process-related dissociation of prefrontal dysfunction in ADHD and conduct disorder patients. Attention-related dysfunction in the ventrolateral prefrontal cortex was seen in ADHD patients, and reward-related dysfunction in the orbitofrontal cortex was seen in conduct disorder patients. These findings, together with the pattern of paralimbic dysfunction demonstrated among children with conduct disorder during sustained attention, support theories of abnormalities in orbitofrontal-paralimbic motivation networks in individuals with conduct disorder and, in contrast, ventrolateral fronto-cerebellar attention network dysfunction in individuals with ADHD.