Continuing implications of the early evidence against the drive-reduction hypothesis of the behavioral effects of drugs

Rationale: Early psychopharmacologists often explained the behavioral effects of drugs as due to changes in the hypothetical construct of motivation, implying that drug effects would depend on the inherent properties of the reinforcer that maintains responding. The work of Dews, Morse, and Kelleher offered an alternative explanation that the scheduling of reinforcers, and the patterns and rates of responding maintained, were more important determinants of drug effects. Objective: The present paper reviews the literature on the influence on drug effects of the type of reinforcer that maintains responding. Methods: Studies that examined the effects of drugs on behaviors maintained by different reinforcers were compared with studies that examined behaviors maintained by the same reinforcer under various conditions. Results: Over a wide range of conditions, the effects of drugs depend more on the schedule-controlled patterns and rates of responding than on the particular reinforcer. However, there are some conditions under which the reinforcer that maintains behavior can also determine drug effects. The broad implications of these findings in selected areas of psychopharmacology are discussed. Conclusions: Under some conditions drug effects are ostensibly consistent with explanations in terms of traditional hypothetical constructs, though under a wide range of other conditions they are not. A more general understanding of the behavioral effects of drugs comes from directing the emphasis of research away from hypothetical constructs and towards the empirically defined determinants of the behavioral effects of drugs.