Semester

Spring

Date of Graduation

2012

Document Type

Thesis

Degree Type

MS

College

Eberly College of Arts and Sciences

Department

Psychology

Committee Chair

Karen G. Anderson.

Abstract

Delay-discounting procedures are commonly employed to study impulsive choice, which can be defined as choice for a smaller, more immediate reinforcer over a larger, more delayed reinforcer. Differences in reinforcer magnitude have been shown to alter delay discounting with human participants, but results have been mixed with non-human animals. It is also unclear what impact the absolute difference between a smaller, more immediate and a larger, more delayed reinforcer has on choice in a delay-discounting context. Therefore, in Experiment 1 of the present study, effects of different reinforcer magnitudes on delay discounting in rats were examined using a discrete-trials procedure where the absolute, but not relative, difference in smaller, immediate and larger, delayed reinforcers was altered. It was found that rates of delay discounting were lower when choice was between one immediate and three delayed reinforcers (Small-Magnitude Condition), compared to when choice was between two immediate and six delayed reinforcers (Large-Magnitude Condition). d-Amphetamine has been found to alter delay discounting, and baseline levels of delay discounting have been found to be correlated with effects of d-amphetamine on choice. As reinforcer magnitude altered baseline rates of delay discounting in Experiment 1, in Experiment 2, effects of various doses of d-amphetamine (0.1, 0.3, 1.0, and 1.8 mg/kg) on delay discounting were examined in the context arranged in Experiment 1. In general, d-amphetamine decreased delay discounting when rates were relatively high (Small-Magnitude Condition) and increased delay discounting when rates were relatively low (Large-Magnitude Condition), suggesting that baseline rates of delay discounting can influence effects of d-amphetamine on delay discounting.

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