A CRITIQUE OF FIXED AND PROGRESSIVE RATIO SCHEDULES USED TO EXAMINE THE NEURAL SUBSTRATES OF DRUG REINFORCEMENT

This paper is a critique of fixed and progressive ratio schedules used to examine the neural substrates of cocaine reinforcement. The discus sion focuses on problems encountered while examining the effects of ne urotoxic lesions and pharmacological pretreatments on cocaine reinforc ement, We review the theoretical and interpretational problems associa ted with the use of the fixed ratio (FR) schedules that have been used in the majority of studies, and we conclude that rate of drug intake cannot directly address the issue of increased or decreased reinforcer efficacy. The progressive ratio (PR) schedule offers some advantages over FR schedules, although it is now clear that the same implementati on cannot be applied across all drug classes. It is likely that the mo tivation to self-administer psychostimulant vs. opiate drugs is qualit ative ly different. We conclude that there is no single schedule that can quantify all aspects of drug reinforcement and that behavioral par adigms will need to be adapted according to the particular question un der study. (C) 1997 Elsevier Science Inc.