Reduced Activation in the Pallidal-Thalamic-Motor Pathway Is Associated With Deficits in Reward-Modulated Inhibitory...

Attention-deficit/hyperactivity disorder (ADHD) symptoms persist into adulthood and are associated with functional impairments. Neuroimaging studies of reward-modulated inhibitory control can identify potential objective markers of impairment and may deepen our understanding of why probands engage in costly behaviors leading to adverse outcomes. The study aimed to identify reward-modulated inhibitory control neural circuitries, their association with ADHD symptoms, and real-world implications of a decreased capacity to engage in reward-modulated inhibitory control.

A total of 106 adults (90% male) with rigorous childhood diagnoses of ADHD were scanned with functional magnetic resonance imaging during the Monetary Incentive Go/NoGo task. Adulthood symptoms of inattention and hyperactivity/impulsivity based on self- and informant report were assessed. The number of lifetime attempts taken to quit smoking were also assessed as an exemplar real-world outcome.

Hyperactivity/impulsivity was negatively associated with activation in the pallidum and primary motor cortex when inhibiting a previously rewarded Go stimulus that yielded a small immediate reward in order to obtain a larger reward later on. Reduced recruitment of the pallidal-thalamic-motor circuit mediated the negative association between hyperactivity/impulsivity and reward-modulated inhibitory control accuracy. Reduced pallidum activation, in response to reward-modulated inhibitory control, was also associated with more attempts made to successfully quit smoking.

Probands with persistent hyperactivity/impulsivity symptoms have alterations in brain regions that calculate the value of inhibiting an action that yields an immediate reward in order to obtain delayed larger rewards. This deficit results in poor inhibitory control on basic tasks and during real-world behaviors that rely on similar processes.