title: Quantitative analyses of methamphetamine's effects on self-control choices: implications for elucidating behavioral mechanisms of drug action.
abstract: The purpose of the present research was to utilize quantitative methods to identify behavioral mechanisms involved in the effects of stimulant drugs on choice in a self-control procedure. A logarithmic equation based upon a combination of the matching law and hyperbolic discounting was used to separate drug-induced changes in sensitivity to reinforcement delay from drug-induced changes in sensitivity to reinforcement amount. Pigeons responded under a concurrent-chains schedule. In the initial link, two keys were illuminated simultaneously and access to the terminal link was controlled by a single random-interval (RI) schedule; pecks on one or the other key lead to its terminal link with a 0.5 probability. In the terminal links, one alternative provided 1-s access to food (the smaller reinforcer) and the other alternative provided 4-s access to food (the larger reinforcer). The signaled delay to the smaller reinforcer always was 2s, whereas the signaled delay to the larger reinforcer increased from 2 to 40s within each session, across 10-min blocks. In general, intermediate doses of methamphetamine increased preference for the larger more delayed reinforcer. Quantitative analyses indicated that, in most cases, methamphetamine decreased sensitivity to reinforcement delay. In a few instances, concomitant decreases in sensitivity to reinforcement amount also occurred. These results suggest that a reduced sensitivity to reinforcement delay may be important behavioral mechanism of the effects of stimulants on self-control choices, and that this effect sometimes can be accompanied by a decreased sensitivity to reinforcement amount.
authors.affiliation: Department of Psychology, University of North Carolina-Wilmington, 601 S. College Rd., Wilmington, NC 28403-5612, USA. pittsr@uncw.edu
authors.forename: Raymond C
authors.initials: RC
authors.lastname: Pitts
authors.forename: Stacy M
authors.initials: SM
authors.lastname: Febbo
mesh_terms: D000818:Animals; D001522:Behavior, Animal / Q000187:drug effects*; D000697:Central Nervous System Stimulants / Q000008:administration & dosage / Q000494:pharmacology*; D002755:Choice Behavior; D010856:Columbidae; D003216:Conditioning, Operant / Q000187:drug effects; D004305:Dose-Response Relationship, Drug; D004334:Drug Administration Schedule; D008694:Methamphetamine / Q000008:administration & dosage / Q000494:pharmacology*; D008960:Models, Psychological; D011336:Probability; D012054:Reinforcement, Psychology
chemical_list: D000697:Central Nervous System Stimulants; D008694:Methamphetamine