|Delay Discounting in the Human and Nonhuman Laboratories: Effects of History, Drug Administration, and Commodity Type
|Monday, October 7, 2013
|12:30 PM–1:50 PM
|Yucatan IV (Fiesta Americana)
|Area: EAB/BPH; Domain: Experimental Analysis
|Chair: Jeffrey S. Stein (Utah State University)
|Abstract: Delay discounting quantifies the devaluation of future outcomes, wherein rapid devaluation corresponds to preference for small, relatively immediate rewards over larger, but delayed, alternatives (i.e., impulsive choice). Over nearly two decades, an influx of human research has clearly established an association between rapid delay discounting (or impulsive choice) and a range of maladaptive behavior, including drug abuse/dependence, gambling, binge eating, and obesity. However, attempts to identify variables that systematically affect delay discounting have been somewhat less successful. The present symposium highlights recent human and nonhuman research designed to examine the behavioral effects of a range of such variables.
|Keyword(s): cocaine, delay discounting, environmental enrichment, methamphetamine
|Impulsive Choice, Alcohol Consumption, and Prolonged Pre-Exposure to Delayed Reinforcement in Rats
|JEFFREY S. STEIN (Utah State University), Renee Renda (Utah State University), Shayne Barker (Utah State University), Kennan J. Liston (Utah State University), Gregory J. Madden (Utah State University)
|Abstract: Impulsive choice (i.e., preference for reinforcement immediacy over magnitude) co-occurs with drug abuse/dependence in humans and greater drug self-administration in rodents. In order to identify potential functional relations, treatment variables that reliably impact impulsive choice may be utilized to investigate concomitant effects on drug self-administration. A recent study in our lab demonstrated reductions in impulsive choice in rats following prolonged pre-exposure to delayed reinforcement (PPDR). However, experimentally induced low levels of impulsive choice were unexpectedly accompanied by increased alcohol consumption—a finding contrary to the relation reported when naturally occurring impulsive choice has been investigated. In the present series of studies, we are investigating potential mechanisms of PPDR’s effects on impulsive choice and alcohol consumption by obtaining measures of sucrose consumption, stress-sensitive open-field behavior, and timing in groups of delay-exposed and non-exposed Long-Evans rats (n = 30 each). Observed outcomes are being compared to identical measures in two separate groups (n = 30 each) that demonstrate naturally occurring differences in impulsive choice similar to those produced by PPDR and control treatments. In the study of naturally occurring impulsive choice, low-impulsive rats appeared to consume more alcohol than high-impulsive rats. However, this potential effect is modest and awaits further analyses (e.g., inclusion of relevant covariates). No significant relation between naturally occurring impulsive choice and any other outcome variable has been observed. Additional PPDR data to be collected.
|Differential Rearing Effects on Impulsivity
|KIMBERLY KIRKPATRICK (Kansas State University), Andrew Marshall (Kansas State University)
|Abstract: Rats were reared in enriched (EC) or isolated conditions (IC) and then tested for different aspects of impulsive behavior. In Experiment 1, the rats were assessed on an impulsive choice task (10 s delay for 1 pellet vs. 30 s delay for 2 pellets), a reward challenge (30 s delay for 1 pellet vs. 30 s delay for 2 pellets) and differential reinforcement of low rate (DRL) tasks. The EC rats chose the larger later (LL) more often on the impulsive choice task, chose the larger reward less often on the reward challenge task, and were less efficient on the DRL task. In Experiment 2, the rats were tested on a reward sensitivity task with different reward magnitudes. The IC rats displayed superior reward discrimination. In Experiment 3, the rats received an impulsive choice task where the LL magnitude increased from 1 to 3 pellets across phases. The EC rats again made more LL choices at the larger magnitudes and displayed more adaptable choice behavior. The combined results are consistent with increased reward sensitivity and increased sensitivity to local reinforcement rate in the IC rats, leading to increased impulsive choice and decreased impulsive action.
|Effects of Oral Methamphetamine on Discounting of Delayed Monetary and Sexual Outcomes in Stimulant Users
|PATRICK S. JOHNSON (Johns Hopkins University), Natalie Rose Bruner (Johns Hopkins University School of Medicine), Matthew W. Johnson (Johns Hopkins University School of Medicine)
|Abstract: Methamphetamine use is a persistent public health problem and is associated with high rates of “impulsivity,” including a greater potential for engagement in sexual risk behavior. Methamphetamine use disorder is also associated with increased delay discounting (preference for smaller immediate over larger later rewards), which may increase vulnerability to transmission of STIs such as HIV/AIDS. In an attempt to model the acute effects of methamphetamine on delay discounting, this within-subjects, double-blind, overnight laboratory study is administering oral placebo or methamphetamine (0, 20 or 40 mg) in each of 3 sessions to non-treatment seeking stimulant users. On the first day of each session, participants are administered a placebo or methamphetamine dose and complete tasks assessing discounting of hypothetical delayed outcomes, including money and sexual outcomes. For sexual outcomes, participants are given repeated hypothetical choices between immediate unprotected sex or delayed protected sex (i.e., with a condom), with self-selected photographed individuals. Following Day 1, participants are monitored overnight. On Day 2, tasks are administered again to assess the effect of methamphetamine-disturbed sleep on delay discounting. Preliminary data from the first participant are generally consistent with previous discounting findings (e.g., decrease in value with increasing delay to the outcome). Additional data to be collected will test whether increases in delay discounting resulting from acute methamphetamine are associated with increased sexual risk (and therefore STI transmission) in stimulant users.
|Cross-Commodity Discounting of Cocaine and Money in Cocaine Users and Community Controls
|MIKHAIL KOFFARNUS (Virginia Tech Carilion Research Institute), Terry M. Lorenz (Virginia Tech Carilion Research Institute), Michael J. Wesley (Virginia Tech Carilion Research Institute), P. Read Montague (Virginia Tech Carilion Research Institute), Warren K. Bickel (Virginia Tech Carilion Research Institute and Department of Psychology, Virginia Tech)
|Abstract: The rate at which an individual discounts the value of a delayed commodity is known to differ substantially among commodities. Typically, drug users discount the value of delayed drug to a greater extent than delayed money. In the present experiment, chronic cocaine users and community control participants completed four discounting tasks that presented choices between money and cocaine available immediately or after a delay: immediate money versus delayed money, immediate cocaine versus delayed cocaine, immediate money versus delayed cocaine, and immediate cocaine versus delayed money. Discount rates of control participants varied widely among the task types, with very high discount rates for the immediate money versus delayed cocaine condition, low discount rates for the immediate cocaine versus delayed money condition, and intermediate rates when both commodities were the same. Conversely, discount rates across commodity combinations were more similar for the cocaine users. These participants’ discount rates in the two conditions with money as the delayed commodity were lower than the two conditions where cocaine was the delayed commodity, independent of the immediate commodity in both cases. Results suggest discount rates vary by commodity differently between cocaine users and controls.