CONCURRENT PERFORMANCES: REINFORCEMENT BY DIFFERENT DOSES OF INTRAVENOUS COCAINE IN RHESUS MONKEYS 1

Abstract

Different doses of intravenous cocaine reinforced the lever pressing of rhesus monkeys under two‐lever concurrent or concurrent‐chain schedules. Under the concurrent procedure, responding produced drug reinforcers arranged according to independent variable‐interval 1‐min schedules. Under the concurrent‐chain procedure, responding in the variable‐interval link led to one of two mutually exclusive, equal‐valued, fixed‐ratio links; Final Acceptance completion of the ratio produced a drug reinforcer. Under both procedures, responding on one lever produced a constant dose of 0.05 or 0.1 mg/kg/injection, while on the other lever, dose was systematically varied within a range of 0.013 to 0.8 mg/kg/injection. Preference, indicated by relative response frequency on the variable‐dose lever during the variable‐interval link, was always for the larger of the doses. Relative response frequencies on the variable‐dose lever roughly matched relative drug intake (mg/kg of drug obtained on variable lever divided by mg/kg of drug obtained on both levers). For many dose comparisons, responding occurred and reinforcers were obtained almost exclusively on the preferred lever. Overall variable‐interval rates generally were lower than with other reinforcers, and these low rates, under the experimental conditions, may have occasioned the exclusive preferences.