Such decreased sensitivity to non-drug related reward has been explained as an allostatic adaptation59. In this interpretation, frequent and high-dose drug use leads to compensatory brain changes that limit appetitive hedonic and motivational processes (‘reward’), instead strengthening aversive (opponent or ‘anti-reward’) systems60. This process is similar to tolerance, in which sensitivity to reward is decreased. It is also captured by the opponent-process hypothesis set forth by Slomon and Corbit61,62, which describes the temporal dynamics of opposing emotional responses; here, negative reinforcement (for example, withdrawal) prevails over positive reinforcement (for example, drug-induced high) in the transition from occasional drug use to addiction. This process is relevant to emotional reactivity and emotion regulation, which, insofar as emotions are defined as ‘states elicited by reinforcers’63, are bound to be impaired in drug addiction, especially during drug-biased processing such as craving and bingeing.
