Collapsing the cycles of impulsivity and compulsivity yields a composite addiction cycle comprised of three stages—preoccupation/anticipation, binge/intoxication, and withdrawal/negative affect—where impulsivity often dominates at the early stages and compulsivity dominates at terminal stages. As an individual moves from impulsivity to compulsivity, a shift occurs from positive reinforcement driving the motivated behavior to negative reinforcement driving the motivated behavior (Koob, 2004). Negative reinforcement can be defined as the process by which removal of an aversive stimulus (e.g., negative emotional state of drug withdrawal) increases the probability of a response (e.g., dependence-induced drug intake). These three stages are conceptualized as interacting with each other, becoming more intense, and ultimately leading to the pathological state known as addiction (Koob and Le Moal, 1997) (Table 1). The present review will focus on the role of an animal model of compulsivity that derives from the negative emotional state of the withdrawal/negative affect stage of the addiction cycle.
