Long-term contrafreeloading in rats during continuous sessions

Abstract

Two rats lived in experimental chambers with continuous access to free food. Leverpressing was reinforced with food on various ratio schedules. Both rats maintained leverpressing under these conditions for several months; however, leverpressing was not an increasing function of the ratio, as previously found for rats in continuous sessions without alternative food. Instead, the function was nonmonotonic or decreasing, and the proportion offood obtained by leverpressing decreased continuously as the ratio increased. These findings are consistent with an economic analysis of the elasticity of demand.In this study, we explored two apparently unrelated problems: contrafreeloading, defined as the establishment and maintenance of operant behavior by food reinforcement despite the simultaneous availability of free food; and performance on ratio schedules in closed economies.Contrafreeloading was first demonstrated in rats by Jensen (1963), who studied food-deprived rats in single 40-min test sessions and showed that leverpressing on a continuous reinforcement (CRF) schedule in the presence of free food was an increasing function of the number of reinforcers before the free food was introduced. Similar procedures have generally been employed in subsequent research, but it is not necessary for rats to have experience with response-contingent reinforcement or to be tested in discrete sessions with controlled deprivation in order for them to exhibit contrafreeloading. When naive rats were continuously housed in operant chambers with both free and response-contingent food available on CRF, leverpressing was acquired and maintained for 30 or 100 days (Coburn & Tarte, 1976;Kopp, Bourland, Tarte, & Vernon, 1976).When rats live continuously in experimental chambers with no food other than that produced by responding, their daily response rates increase as the value of a fixed ratio (FR) schedule is increased from CRF to FR240, so that roughly constant food intake is maintained (Collier, Hirsch, & Hamlin, 1972; see also Collier, Johnson, Hill, & Kaufman, 1986). This situation is referred to as a closed economy (see, e.g., Collier, 1983;Hursh, 1984). The hallmark of a closed economy is that the experimenter does not arrange extraexperimental feeding, so that the subject regulates its own deprivation level. This aspect of a closed economy is maintained even if free food is continuously available within the experimental environment. We therefore examined performance in a closed Correspondence should be addressed to Sandra Rutter, Department of Psychology, Conant Hall, University of New Hampshire, Durham, NH 03824-3567.Copyright 1990 Psychonomic Society, Inc. 556 economy with free food available, and asked whether rats would adjust their response rates to obtain a constant number of response-contingent food reinforcers when ratio schedules were varied, as they do when there is no other source of food. METHOD Subjects and ApparatusTwo male Harvard-strain brown rats served. They each lived continuously in a standard Lehigh Valley op...

The influence of cost manipulation on water contrafreeloading induced by repeated exposure to quinpirole in the rat

“…Summing up, vehicle-treated animals easily adapted to changes in the reinforcing contingencies; thus, under conditions of operant access (days 1-6), they increased lever pressing according to the FR in order to maintain asymptotic levels of water intake, whereas lever pressing dropped to minimal levels when water was also freely available (days 7-15). This finding is consistent with the observation that under CFL conditions, demand for food becomes elastic, and responding drops considerably when the FR increases (Rutter and Nevin 1990). Quite the opposite where, under QNP, lever pressing for water as a function of FR remained almost identical in Fig.…”

“…First, we studied CFL under conditions of a single fixed ratio schedule of reinforcement (FR3). CFL for food has been found elastic, since responding markedly decreased as the ratio requirement increased (Rutter and Nevin 1990), but prolonged stimulation of dopaminergic D2/ D3 receptors is expected to affect this spontaneous pattern of responding. Salamone et al (2001Salamone et al ( , 2002 extensively examined the effect on food-reinforced behavior after striatal DA depletion or pharmacological inhibition in rats under different fixed ratio schedules of reinforcement, demonstrating that, while performance on a minimal work requirement was unaffected by these manipulations, instrumental lever pressing became sensitive to more costly schedules.…”

Early life adversity increases foraging and information gathering in European starlings, Sturnus vulgaris

“…In the wild, developmental disadvantage could be predictive of a more uncertain environment per se independent of competition, perhaps selecting for developmentally plastic strategies to insure against or reduce uncertainty via sampling the environment by CFL. In opposition to these hypotheses, CFL has been shown to be reduced by increased environmental uncertainty ( Forkman, 1991 ) as well as by increased effort to obtain earned food ( Rutter & Nevin, 1990 ), both of which are likely to result from inferiority in social competition.…”