Assessing the inhibitory properties of a latent inhibitor in flavor-aversion learning

In Experiment 1, rats received 16 nonreinforced trials of exposure to a flavor (A) that was subsequently used as the conditioned stimulus in flavor-aversion conditioning. In the critical condition, Flavor A was presented in compound with a different novel flavor on each of the eight daily trials. This treatment produced latent inhibition, in that this preexposure retarded conditioning just as did 16 trials with A alone. Rats in the control conditions, given no preexposure or exposure just to the sequence of novel flavors, learned readily. Experiment 2 examined the effects of these forms of preexposure on performance on a summation test, in which Flavor A was presented in compound with a separately conditioned flavor (X). The preexposure procedure in which A was presented along with novel flavors rendered A effective in inhibiting the response conditioned to X on that test. The conclusion, that this form of training can establish the target stimulus as a conditioned inhibitor, is predicted by the account of latent inhibition put forward by Hall and Rodríguez (2010) which proposes that the latent inhibition effect is a consequence both of a reduction in the associability of the stimulus and of a process of inhibitory associative learning that opposes the initial expectation that a novel event will be followed by some consequence.

Flavor Aversion Learning Based on Running: A Review

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.