Rats assess costs and benefits according to an internal standard

Abstract

Variation in effort to obtain rewards is a fact of mammalian everyday life. In this study, we assess how rats scale variable costs and benefits. Different groups of rats were trained in a T-maze to discriminate a high (three or five sugar pellets) from a low reward (one sugar pellet) arm. Subsequently barriers were introduced at the high and low reward side such that the overall long-term pay-off of the high reward arm finally became lower than that of the low reward arm. The data show that under different regimes of costs (climbing barriers) and benefits (number of rewards) of the two arms rats appear to shift their behaviour towards the better side according to a constant relative cost-benefit ratio between the arms. Such a ratio allows them to deal with variation in the (physical appearance of) costs and benefits and choose the best long-term option. © 2006 Elsevier B.V. All rights reserved.Keywords: Rats; Iowa gambling task; Sugar pellets; T-maze; Barriers; Cost-benefit assessment Variation in reward quality and magnitude is the rule rather than the exception for most organisms living under natural conditions. Therefore, both human and non-human animals trade off costs and benefits to optimise long-term behaviour [8,15]. As an example, it has been shown that humans choose the option with the best long-term pay-off in the Iowa Gambling Task, which contains moment-to-moment variation in costs (monetary losses) and benefits (monetary wins; 1). Effort to obtain rewards is another crucial factor in cost-benefit analyses. Several studies have been performed showing that animals assess costs and benefits of different options [6,7,[11][12][13]. These studies have shown that choice behaviour of animals is determined by the number of food items that can be obtained and the barriers that need to be crossed. However, it has not been assessed thus far how cost-benefit ratios of different options are directly compared and how moment-to-moment variation in effort and reward affects long-term choice behaviour when multiple options exist. Given the efficiency of behaviour in an environment that contains variation [8,15] it may be hypothesized that human and non-human animals scale variable costs and benefits according to a constant relative cost-benefit ratio. This allows them to deal with a * Corresponding author. Tel.: +31 30 2534373; fax: +31 30 2539227. E-mail address: R.vandenbos@las.vet.uu.nl (R. van den Bos).large number of costs and benefits, differing in actual (physical) appearance. We tested this in rats using a T-maze in which we introduced variation in rewards and effort.For this experiment, n = 17 Wistar rats (HsdCpb:WU, Harlan, The Netherlands) were used. All rats had already participated in another cost-benefit assessment experiment, which took place in a box different from the present experiment. They had been trained to discriminate arms differing in the proportion of sugar over quinine treated sugar pellets [2]. There was no evidence that this experiment had any effect on the present experiment. Al...

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Intra-accumbens injections of the adenosine A2A agonist CGS 21680 affect effort-related choice behavior in rats

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