ABSTRACT
Most adults have at one point in their life used a potentially addictive substance, if legal, illicit or prescription drugs are included. Yet relatively few develop sufficient problems to meet the formal criteria for drug addiction, even for potent illegal drugs such as cocaine or heroin. The same is true for substances and activities that carry a similar potential for abuse and addiction, such as gambling and highly processed sugary foods. For all of these, addiction is characterized as a compulsive behavior consisting of overwhelming involvement with procurement and consumption of the reward, persistence in the face of increasing costs, and a loss of control and narrowing of interests away from other forms of reward besides the reward of choice. The essence of the incentive-sensitization hypothesis is that the core features of addiction result from mesocorticolimbic hypersensitivity to drugs and to drug-related cues, resulting from neuroadaptations, which produces excessive and narrowly focused ‘wanting’ or incentive salience to obtain and consume the addictive target. Individuals differ in susceptibility to drug-induced sensitization, and differ in patterns of drug-taking that can determine whether and how much incentive-sensitization they eventually incur (Allain et al. 2015). For those who do become sensitized, mesolimbic interactions with corticolimbic circuitry focus excessive desire specifically on that target of addiction, resulting in surges of enhanced ‘wanting’ of the addictive target upon encountering related cues or vivid imagery. Incentive-sensitization persists even after drug consumption stops and after withdrawal symptoms end, contributing to the chief problem in treating drug addiction, namely relapse. Even after prolonged periods of withdrawal and abstinence, a high percentage of addicted individuals in treatment programs eventually relapse to drug taking. For example, in a study of heroin users, relapse rates to re-use after cessation were approximately 60% within 3 months and at least 75% within 12 months. For this reason, drug addiction is characterized as a chronic relapsing disorder; relapse is the rule rather than the exception, and often occurs repeatedly. The persistence of incentive-sensitization may be a reason why successful abstinence from addiction can require years or even decades of effort. Many who are addicted in their teens or 20s eventually do escape in their 30s (Heyman 2009). Those successes may also involve major changes to life contexts that previously acted as triggering cues for sensitized ‘wanting’, so that remaining sensitization is no longer so detrimentally expressed. Conceivably, a decline in the intensity of sensitized ‘wanting’ peaks may also be aided by the 352natural age-related decay of brain dopamine systems that occurs after the 20s (Mukherjee et al. 2002). And still, some addicts never do fully escape, not even in their 40s, 50s, 60s or beyond – a potential testimony to the enduring persistence of incentive sensitization.
