Abstract
Wheel running establishes aversion in rats to a flavored solution consumed shortly before the running. Many studies have shown that this is a case of Pavlovian conditioning, in which the flavor and running respectively act as the conditioned stimulus (CS) and the unconditioned stimulus (US). The present article introduces some procedural variables of this running-based flavor aversion learning (FAL), including subjects, CS agents, US agents, and drive operations. This article also summarize various behavioral features of Pavlovian conditioning demonstrated in running-based FAL including the law of contiguity despite long-delay learning, extinction and spontaneous recovery, CS-preexposure effect, remote and proximal US-preexposure effects, degraded contingency effect, inhibitory learning by backward conditioning, stimulus overshadowing, associative blocking, and higher-order contextual control. Also reviewed are several hypotheses proposed for the underlying psychophysiological causes of running-based FAL (activation of mesolimbic dopamine system, gastrointestinal discomfort, motion sickness, energy expenditure, general stress, and anticipatory contrast). At the end of the article, we visit the question of most general interest about running-based FAL: why pleasurable activity of voluntary running yields aversive learning in rats.
Highlights
After several failures to obtain a reliable effect in mice, we successfully demonstrated it (Nakajima & Oi, 2018): Water-deprived mice were given a 15-min access to 0.2% saccharin solution in the drinking chambers followed by a 30-min confinement in the wheels (Group Run, n = 4) or by a 30-min stay in the drinking chambers (Group NoRun, n = 4)
The degree of running-based flavor aversion is a positive function of the length of time that rats are confined to unlocked wheels
This claim comes from the results of Hayashi et al (2002) who compared multi-trial flavor aversion learning (FAL) based on 5, 15, and 30-min running opportunities and of Masaki and Nakajima (2006) who assessed one-trial FAL based on 15, 30, 60, and 120-min running opportunities
Summary
Wheel running establishes aversion in rats to a flavored solution consumed shortly before the running. US Agents Many studies on running-based FAL employed closed and freely moving activity wheels for creating flavor aversion in the rats. After the drinking period, 4 rats were confined to locked wheels for 30 min, while the remaining 3 rats were in unlocked wheels for the same period The latter rats acquired aversion to the target flavor as illustrated in the conditioning performance and in the post-training choice test performance. The degree of running-based flavor aversion is a positive function of the length of time (duration) that rats are confined to unlocked wheels This claim comes from the results of Hayashi et al (2002) who compared multi-trial FAL based on 5-, 15-, and 30-min running opportunities and of Masaki and Nakajima (2006) who assessed one-trial FAL based on 15-, 30-, 60-, and 120-min running opportunities (see the second section of Figure 5). Simultaneous conditioning procedures (swimming in flavored water) yield a very weak flavor aversion
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