Neural Mechanisms of Reward Learning and Cognitive Control in Children with Attention Deficit Hyperactivity Disorder

Attention Deficit Hyperactivity Disorder (ADHD), is characterized by its behavioural manifestations including difficulties with attention, hyperactivity and impulsivity. It is one of the most common childhood disorders with a prevalence rate of three to seven percent of school-aged children. ADHD carries a significant impact not only on children diagnosed with this disorder, but also on their families, schools, communities and the health care system. Numerous theories of ADHD have focused on deficits in executive functions, specifically cognitive control and the inability to inhibit inappropriate behaviours. Neuropsychological and neuroimaging studies in children with ADHD support a theory of frontal-subcortical dysfunction: specifically, a dysfunction in the midbrain dopamine (DA) system that may result in an impaired midbrain DA system and reinforcement learning, or the ability to learn to modify behaviour on the basis of rewarding and punishing stimuli in the environment. Furthermore, recent developments in reinforcement learning theory indicate that the midbrain DA system carries Reward Prediction Error (RPE) signals. Carmen Lukie is investigating how a midbrain DA system for reinforcement learning may be impaired in children with ADHD. This study follows on from her earlier research which showed that children with ADHD are particularly sensitive to the saliency of rewards. Specifically, she found that RPE signals in children with ADHD are modulated by the context in which feedback is given, and differs from what is observed in typically developing children. The current study will replicate this finding, while correcting for the limitations of the earlier study. Ultimately, the results of this research could lead to the development of novel, more effective behavioural and pharmacological treatments. Further, the research may expand to include individuals with substance abuse, pathological gambling, conduct and borderline personality disorders.