Drug Discrimination Under Concurrent Variable‐ratio Variable‐ratio Schedules

Abstract

Pigeons were trained to discriminate 5 mg/kg pentobarbital from saline under concurrent variable-ratio (VR) VR schedules, in which responses on the pentobarbital-biased lever were reinforced under the VR schedule with the smaller response requirements when pentobarbital was given before the session, and responses on the saline-biased key were reinforced under the VR schedule with the larger response requirements. When saline was administered before the session, the reinforcement contingencies associated with the two response keys were reversed. When responding stabilized under concurrent VR 20 VR 30, concurrent VR 10 VR 40, or concurrent VR 5 VR 50 schedules, pigeons responded almost exclusively on the key on which fewer responses were required to produce the reinforcer. When other doses of pentobarbital and other drugs were substituted for the training dose, low doses of all drugs produced responding on the saline-biased key. Higher doses of pentobarbital and chlordiazepoxide produced responding only on the pentobarbital-biased key, whereas higher doses of ethanol and phencyclidine produced responding only on this key less often. d-Amphetamine produced responding primarily on the saline-biased key. When drugs generalized to pentobarbital, the shape of the generalization curve under concurrent VR VR schedules was more often graded than quantal in shape. Thus, drug discrimination can be established under concurrent VR VR schedules, but the shapes of drug-discrimination dose-response curves under concurrent VR VR schedules more closely resemble those seen under interval schedules than those seen under fixed-ratio schedules. Graded dose-response curves under concurrent VR VR schedules may relate to probability matching and difficulty in discriminating differences in reinforcement frequency.

Drug discrimination and the analysis of private events.

“…The extent to which this is a fundamental characteristic of behavior under the control of drug discriminative stimuli or an outcome of the particular training parameters remains unclear. The few drug discrimination studies that have used variable-ratio schedules have produced relatively graded dose–response functions in individual subjects (Holloway & Gauvin, 1989; McMillan, Hardwick, & Li, 2002). Determining the conditions under which drug discrimination and generalization is quantal or graded would provide fundamental information regarding private responses to drug stimuli.…”

Persistent preference in concurrent-chain schedules.

“…That is, behavior is allocated between concurrently available sources of reinforcement so as to match the relative rates of reinforcement obtained from those alternatives. In addition, it has been shown that preference exists for variable over fixed schedules or reinforcement (Ahearn, Hineline, & David, 1992; Field, Tonneaau, Ahearn, & Hineline, 1996), and for the smaller ratio in concurrent variable-ratio (VR) schedules (Hernstein and Loveland, 1975; MacDonall, 1988; McMillan, Hardwick & Li, 2002).…”