In the following sections, we will discuss the empirical data linking various forms of impulsive behavior, measured in humans and laboratory animals, to drug-seeking and –taking; our focus is on those measures of impulsivity whose relationship to addiction has been studied sufficiently – including, impulsive action, waiting behavior and delay- and risk-related decision making. We will then turn to the neural circuitry and pharmacological mechanisms that underpin these forms of impulsive behavior. Our discussion is guided by our view that – if these manifestations of impulsive behavior represent distinct psychological processes, they should relate to addiction-related behaviors in different ways; additionally, they should rely upon substantially non-overlapping neural circuitries and depend upon separable molecular and pharmacological substrates. In his review, Evenden drew upon his own, very comprehensive set of behavioral pharmacological studies, arguing that varieties of impulsive behavior can sometimes show different responses to various drug manipulations.2 This review adds to the discussion by addressing whether unique neural mechanisms predict individual variation in subtypes of impulsivity and whether these varieties of impulsivity exhibit distinct relationships to addiction behaviors.
