ADDICTIVE DRUGS AS REINFORCERS - MULTIPLE PARTIAL ACTIONS ON MEMORY-SYSTEMS

This review applies some new experimental findings and theoretical ide as about how reinforcers act on the neural mechanisms of learning and memory to the problem of how addictive drugs affect behaviour. A basic assumption of this analysis is that all changes in behaviour, includi ng those involved in drug addiction and the initiation of drug self-ad ministration, require the storage of new information in the nervous sy stem. Animal studies suggest that such information is processed in sev eral (this review deals with three) more or less independent learning and memory systems in the mammalian brain. Reinforcers can interact wi th these systems in three ways: they activate neural substrates of obs ervable approach or escape responses, they produce unobservable intern al states that can be perceived as rewarding or aversive, and they mod ulate or enhance the information stored in each of the memory systems. It is suggested that each addictive drug maintains its own self-admin istration by mimicking some subset of these actions. Evidence supporti ng the notion of multiple memory systems and data on the actions of se veral drugs (amphetamine, cocaine, nicotine, alcohol and morphine) on these systems are briefly reviewed. The utility of the concept of ''re ward'' for understanding the effects of drugs on behaviour is discusse d. Evidence demonstrating actions of drugs on multiple neural substrat es of reinforcement suggests that no single factor is likely to explai n either addictive behaviour in general or self-administration in part icular. Some of the findings on the development and maintenance of sel f-administration by animals of the five exemplar drugs are discussed i n the context of these ideas.