REINFORCEMENT PROCESSES IN OPIATE ADDICTION - A HOMEOSTATIC MODEL

The development of tolerance and dependence has traditionally been con sidered an integral aspect of the drug addiction process, and opiate d ependence has been studied extensively as a model system in this regar d. However, recent emphasis on the positive reinforcing properties of drugs has led to the suggestion that tolerance, dependence, and withdr awal may be of secondary or even negligible importance in motivating c ompulsive drug use. The current article argues for an integrated view of addiction in the form df a homeostatic neuroadaptation model which emphasizes the motivational significance of both the positive affectiv e state produced by opiates and the negative affective state character istic of drug withdrawal. The model is supported by evidence at both t he behavioral and neural systems levels of analysis. Understanding the important distinction between somatic and affective components of opi ate withdrawal is key to recognizing the factors which contribute to t he motivational significance of opiate dependence and withdrawal. In a ddition, the critical role of conditioning processes in the maintenanc e of compulsive drug use and relapse after periods of abstention is di scussed. Finally, it is argued that both the positive reinforcement pr oduced by acute administration of a drug and the negative affective st ate produced by withdrawal are common to multiple classes of abused dr ugs, suggesting that an understanding of homeostatic neuroadaptation w ithin motivational systems provides a key to the etiology, treatment a nd prevention of drug addiction.