Collapsing the cycles of impulsivity and compulsivity yields a composite addiction cycle comprising three stages—preoccupation/anticipation, binge/intoxication, and withdrawal/negative affect—in which impulsivity often dominates at the early stages and compulsivity dominates at terminal stages (Fig. 1). 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 to relieve the negative emotional state). Note that negative reinforcement is not punishment, although both involve an aversive stimulus. In punishment, the aversive stimulus suppresses behavior, including drug taking (e.g., disulfiram [Antabuse]). Negative reinforcement can be perhaps described in lay terms as reward via relief (i.e., relief reward), such as removal of pain or in the case of alcoholism removal of the negative emotional state of acute withdrawal or protracted abstinence. The 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) (Fig. 1).
