The Incentive Sensitization Theory of Addiction

Many theoretical constructs have been formulated over the years to explain the phenomenon of addiction. While the incentive sensitization theory of addiction acknowledges the important contributions of many former theories, it postulates that addiction is a state of aberrant motivation. Through repeated drug use, individuals with addiction become hypersensitive to the effects of the drugs themselves and to the stimuli associated with these drugs, including a variety of drug paraphernalia. For all individuals consuming drugs, drug-related stimuli have an inherent predictive value that signals an impending dose of the drug. For people with addiction, these drug cues move beyond being merely predictors for the drug and are imbued with excessive motivational value (called incentive salience); they become powerful motivational magnets capable of instigating and enhancing cravings for the drug. This incentive sensitization occurs through a process of neuroadaptations in the mesocorticolimbic dopamine system that have been shown to be long-lasting. These brain changes yield increasingly intense, highly focused cravings for an addictive target and transform cues related to the target into incentive stimuli that promote compulsive reward-seeking and relapse. The incentive sensitization theory does not deny a role for pleasure, habits, and withdrawal in addiction, but posits that those individuals with addiction (a) continue to take drugs compulsively even while experiencing diminished pleasure, (b) demonstrate creative new ways to procure drugs when necessary, and (c) often relapse well beyond when withdrawal has subsided. The critical factor in the development and maintenance of addiction is the persistent neuroadaptation that sensitizes the attribution of incentive salience to drugs and their cues, which explains why recovering from addiction is a long and slow process. The incentive sensitization theory can account for drug-induced attentional bias as well as how addiction can develop toward nondrug reward sources such as food, sex, and gambling environments.