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| Recent Studies of Variables Affecting Discounting and Demand |
| Sunday, May 30, 2010 |
| 9:00 AM–10:20 AM |
| Lone Star Ballroom Salon F (Grand Hyatt) |
| Area: EAB/BPH; Domain: Experimental Analysis |
| Chair: Paul L. Soto (Johns Hopkins University) |
| Abstract: Delay discounting and behavioral economics are two areas of intense research interest with important contributions to our understanding of basic behavioral processes and with implications for a variety of applied concerns including impulsivity disorders and drug abuse. The following symposium highlights recent research on the impact of a range of variables on delay discounting and economic demand. Paul Soto will discuss the behavioral economic assessment of the effects on food consumption of genetic deletions of dopamine D2 receptors. Jeff Stein will discuss differences in delay discounting performance of different strains of rats assessed using two adjusting-amount procedures. Rachel Cassidy will present data on the effects of open and closed economies, reinforcer size, and nicotine on demand for food. Chad Galuska will talk about the effect of session length on elasticity of demand. The studies presented illustrate the range and depth of behavior analytic studies of delay discounting and economic demand. |
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| Delay Discounting in Lewis and Fischer 344 rats: Implications for the Use of an Adjusting-Amount Procedure to Detect Between-Strain Differences. |
| JEFF S. STEIN (University of Kansas), Jonathan W. Pinkston (UT Health Science Center at San Antonio), Monica T. Francisco (University of Kansas), Adam T. Brewer (University of Kansas), Patrick S. Johnson (University of Kansas), Gregory J. Madden (University of Kansas) |
| Abstract: Strain-related differences in delay discounting are important as they may facilitate the investigation of genetic and neurochemical determinants of choice. Previous studies report that Lewis rats (LEW) make more impulsive choices than Fischer 344 rats (F344). However, a more recent study reports no significant difference between strains in rates of delay discounting. While this finding is at odds with previous reports, delay discounting was assessed with a rapid determination adjusting-amount procedure in which delay was manipulated daily and no stability criteria were used. Such rapid assessments may underestimate more extreme rates of discounting and thus conceal differences between groups. The present study was designed to determine if a steady state adjusting-amount procedure could reproduce the strain difference more consistently reported in the literature. Using such a procedure, Experiment 1 of the present study observed steeper delay discounting in LEW rats (n=7) than F344 rats (n=8) (p<.01). When a close approximation of the rapid determination procedure was used in Experiment 2, no significant difference between strains was observed. Taken together, the results of these experiments suggest that a rapid determination adjusting-amount procedure may be insensitive to differences otherwise detected under steady state assessment. |
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| Effects of Environmental Manipulations and Nicotine on the Essential Value of Food as Measured by the Exponential Demand Equation |
| RACHEL N. CASSIDY (University of Florida), Drake Morgan (University of Florida), Jesse Dallery (University of Florida) |
| Abstract: Rats’ demand for food across a sequence of fixed ratio schedules was assessed under open and closed economy conditions, as well as under 1- and 2-pellet per reinforcer delivery conditions. The Exponential Demand Equation was fitted to the relation between normalized FR value and the logarithm of the normalized reinforcer consumption and estimates of the alpha parameter, a putative measure of value, were compared across conditions. Estimates of alpha varied across the open and closed economy conditions unsystematically. A systematic increase in alpha (decrease in essential value) was found between the one- and two-pellet conditions under the open economy and under the closed economy in three out of four subjects. Subjects were then administered nicotine via osmotic minipumps at a dose of 3 mg/kg/day and exposed to both the one- and two-pellet conditions under a closed economy. Results indicate no systematic effect of nicotine on essential value as measured by the alpha parameter; however, goodness of fit declined across subjects, indicating a deficit in accounting for changes in demand associated with nicotine administration. These data indicate that the alpha parameter merits further exploration before its status as a parameter isomorphic with a behavioral conception of value can be confirmed. |
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| Assessing Economic Demand for Food and Water in Rats under Open Economies of Varying Session Duration |
| CHAD M. GALUSKA (College of Charleston), Vanessa Minervini (College of Charleston), Heather Hagler (College of Charleston) |
| Abstract: In the animal laboratory, it has become standard research methodology to obtain demand curves for appetitive reinforcers under a closed economy where food only can be obtained during the experiment. Demand curves obtained under open economies, where food also is available outside of the experiment, typically are more elastic. We hypothesize that these differences in elasticity may not be fundamental to the economy but rather, in part, reflect differences in the duration of the experimental session. Closed economies typically use extremely long sessions and open economies typically use relatively short sessions. We assessed rats’ demand for food under open economies at session durations ranging from 1 hr to 6 hr. Water was concurrently available under a continuous reinforcement schedule. Consistent with our hypothesis, we found that demand curves obtained using longer sessions approximate those obtained under closed economies. Demand curves obtained using shorter sessions are considerably more elastic. In addition, at shorter session durations, water functions as an economic substitute for food. As session duration increases, water assumes the usual complementary relationship with food. |
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| Assessment of Dopamine D2 Receptor Function in the Reinforcing Effects of Food: Behavioral Economics and the Effects of Prefeeding and Extinction in Knockout Mice |
| PAUL L. SOTO (Johns Hopkins University), David Grandy (Oregon Health and Science University), Steven R. Hursh (Institutes of Behavior Resources), Jonathan L. Katz (National Institute on Drug Abuse) |
| Abstract: The effects of genetic deletions of dopamine (DA) D2 receptors (D2Rs) on food-maintained responding were used to examine the role of DA D2Rs in mediating the process of reinforcement. In addition, the effects of extinction and partial satiation were assessed. Mice responded (lever pressing or nose poking) in daily sessions under FR schedules of food delivery. Response rates of the KO mice were generally lower than those of their WT and HET littermates. Consistent with the notion of a prominent role of the DA D2R in reinforcing efficacy, estimates of a from fits of the exponential model of demand were lowest for WT and highest for KO mice. The effects of prefeeding and extinction did not significantly differ across the three genotypes when results were expressed relative to baseline values. That food-maintained behavior occurred at all in KO mice indicates that the DA D2R is not necessary for reinforcement. The lack of differences among the genotypes in the effects of prefeeding and extinction suggests that these operations are not influenced by DA D2Rs in a substantial way. Nonetheless, an economic analysis indicates that the DA D2R contributes in an important way to reinforcing effectiveness for sustained operant responding. |
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