Delay discounting of food by rhesus monkeys: Cocaine and food choice in isomorphic and allomorphic situations.
Research on delay discounting has focused largely on nondrug reinforcers in an isomorphic context in which choice is between alternatives that involve the same type of reinforcer. Less often, delay discounting has been studied with drug reinforcers in a more ecologically valid allomorphic context where choice is between alternatives involving different types of reinforcers. The present experiment is the first to examine discounting of drug and nondrug reinforcers in both isomorphic and allomorphic situations using a theoretical model (i.e., the hyperbolic discounting function) that allows for comparisons of discounting rates between reinforcer types and amounts. The goal of the current experiment was to examine discounting of a delayed, nondrug reinforcer (food) by male rhesus monkeys when the immediate alternative was either food (isomorphic situation) or cocaine (allomorphic situation). In addition, we sought to determine whether there was a magnitude effect with delayed food in the allomorphic situation. Choice of immediate food and immediate cocaine increased with amount and dose, respectively. Choice functions for immediate food and cocaine generally shifted leftward as delay increased. Compared to isomorphic situations in which food was the immediate alternative, delayed food was discounted more steeply in allomorphic situations where cocaine was the immediate alternative. Notably, discounting was not affected by the magnitude of the delayed reinforcer. These data indicate that how steeply a delayed nondrug reinforcer is discounted may depend more on the qualitative characteristics of the immediate reinforcer and less on the magnitude of the delayed one.
Division of Neurobiology and Behavior Research, Department of Psychiatry and Human Behavior, University of Mississippi Medical Center.
Sally L
SL
Huskinson
Division of Neurobiology and Behavior Research, Department of Psychiatry and Human Behavior, University of Mississippi Medical Center.
William L
WL
Woolverton
Department of Psychology, Washington University.
Leonard
L
Green
Department of Psychology, Washington University.
Joel
J
Myerson
Division of Neurobiology and Behavior Research, Department of Psychiatry and Human Behavior, University of Mississippi Medical Center.
Kevin B
KB
Freeman
D000818:Animals; D002755:Choice Behavior / Q000187:drug effects*; D003042:Cocaine / Q000008:administration & dosage*; D003216:Conditioning, Operant; D065786:Delay Discounting; D018765:Dopamine Uptake Inhibitors / Q000008:administration & dosage*; D004305:Dose-Response Relationship, Drug; D005502:Food; D005518:Food Preferences / Q000187:drug effects* / Q000523:psychology*; D008253:Macaca mulatta; D008297:Male; D012055:Reinforcement Schedule; D012646:Self Administration; D013997:Time Factors
D018765:Dopamine Uptake Inhibitors; D003042:Cocaine