How can one resolve the facts that these arguably separable forms of impulsivity: 1) each have qualitatively similar patterns of predictive value of substance use disorders in humans and drug self-administration in animals, 2) each depend upon partially overlapping neural circuitries and 3) each are sensitive in similar ways to monoaminergic manipulations? Figure 2 shows two potential models that could explain these facts; these two models are certainly not the only possibilities but may be instructive in any case. One model (Figure 2A) suggests that each of the forms of impulsivity share some variance and mechanism with one another but that each shares a unique set of variance and mechanism with addictions. This model says that the correspondences in Figure 2 and Table 2 are instructive about the relationships between forms of impulsivity but not about their individual relationships to addictions. It suggests that other mechanisms, perhaps one unknown to use, explain these individual predictive relationships.
