Recent theories have proposed that ADHD arises from alterations in multiple neural pathways (Nigg and Casey, 2005; Sonuga-Barke, 2005). Nigg and Casey (2005) theorized that impairment in cognitive control circuits would contribute to executive dysfunctions, while impairment in affective and reward systems would lead to altered signaling of rewards and consequently to atypical approach and avoidance behaviors. They hypothesized that individuals with ADHD fail to estimate future consequences (future reward or non-reward), and thus exhibit behavior characterized by excessive approach (Nigg and Casey, 2005). Their idea is broadly similar to that of Sonuga-Barke (2005), who hypothesized that two pathways are involved in ADHD: (1) changes within the executive circuit, resulting in executive/inhibitory deficits, and (2) alterations in the reward circuit, resulting in delay aversion (Sonuga-Barke, 2005).
