An analysis of reinstatement after extinction of a conditioned taste aversion.

Taste aversion learning has sometimes been considered a specialized form of learning. In several other conditioning preparations, after a conditioned stimulus (CS) is conditioned and extinguished, reexposure to the unconditioned stimulus (US) by itself can reinstate the extinguished conditioned response. Reinstatement has been widely studied in fear and appetitive Pavlovian conditioning, as well as operant conditioning, but its status in taste aversion learning is more controversial. Six taste-aversion experiments with rats therefore sought to discover conditions that might encourage it there. The results often yielded little to no evidence of reinstatement, and we also found no evidence of concurrent recovery, a related phenomenon in which responding to a CS that has been conditioned and extinguished is restored if a second CS is separately conditioned. However, a key result was that reinstatement occurred when the conditioning procedure involved multiple closely spaced conditioning trials that could have allowed the animal to learn that a US presentation signaled or set the occasion for another trial with a US. Such a mechanism is precluded in many taste aversion experiments because they often use very few conditioning trials. Overall, the results suggest that taste aversion learning is experimentally unique, though not necessarily biologically or evolutionarily unique. (PsycInfo Database Record (c) 2024 APA, all rights reserved).

Partial reinforcement effects on acquisition and extinction of a conditioned taste aversion.

Four experiments with rat subjects asked whether a partial reinforcement extinction effect (PREE) occurs in taste aversion learning. The question has received little attention in the literature, and to our knowledge no taste aversion experiment has previously demonstrated a PREE. In each of the present experiments, experimental groups received a taste mixed in drinking water for 20 min; such taste exposures were sometimes paired with a lithium chloride (LiCl) injection and sometimes not. Control groups received only taste-LiCl pairings. There was evidence that each reinforced and non-reinforced trial produced increments and decrements in aversion strength (respectively), and trials mattered more than accumulated time during the conditioned stimulus and during the background (as emphasized in time-accumulation models like those of Gallistel and Gibbon, Psychological Review, 107, 289-344, 2000, and Gibbon and Balsam, Autoshaping and conditioning theory, Academic Press, New York, pp. 219-235, 1981). In addition, a partial reinforcement extinction effect was observed when there was a relatively large number of conditioning trials. The results extend our understanding of extinction in taste aversion learning and provide more evidence that aversion learning might follow rules that are qualitatively similar to those of other forms of learning.

Reinforcer predictability and stimulus salience promote discriminated habit learning.

Instrumental (operant) behavior can be goal directed, but after extended practice it can become a habit triggered by environmental stimuli. There is little information, however, about the variables that encourage habit learning, or about the development of discriminated habits that are actually triggered by specific stimuli. (Most studies of habit in animal learning have used free-operant methods.) In the present experiments, rats received training in which a lever press was reinforced only in the presence of a discrete stimulus (S) and the status of the behavior as goal-directed or habitual was determined by reinforcer devaluation tests. Experiment 1 compared lever insertion and an auditory cue (tone) in their ability to support habit learning. Despite prior speculation in the literature, the "salient" lever insertion S was not better than the tone at supporting habit, although the rats learned more rapidly to respond in its presence. Experiment 2 then examined the role of reinforcer predictability with the brief (6-s) tone S. Lever pressing during the tone was reinforced on either every trial or on 50% of trials; habit was observed only with the highly predictable (100%) relationship between S and the reinforcer. Experiment 3 replicated this effect with the tone in a modified procedure and found that lever insertion contrastingly encouraged habit regardless of reinforcer predictability. The results support an interactive role for reinforcer predictability and stimulus salience in discriminated habit learning. (PsycInfo Database Record (c) 2021 APA, all rights reserved).

Can the discriminative stimulus effects of nicotine function concurrently as modulatory opponents in operant and pavlovian occasion setting paradigms in rats?

Nicotine promotes interoceptive changes in the nervous system. Such interoceptive stimuli play important roles in modulating addictive behavior. Operant and Pavlovian stimulus control modulate responsiveness to environmental stimuli related to drug-seeking and self-administration. Nicotine functions as a discriminative stimulus in modulating operant behavior as well as Pavlovian feature stimuli in modulating the conditional responding (CR) to exteroceptive CS→US contingencies. Elucidation of the interaction of these interoceptive stimulus control functions is vital for a comprehensive understanding of nicotine use/abuse, which might lead to better behavioral treatment strategies. This experiment evaluated the interaction among Pavlovian feature positive (FP) and feature negative (FN) effects of nicotine on concurrently occurring operant SD and SΔ effects. Sixteen rats were trained in a Pavlovian and operant bidirectional contingency paradigm, using nicotine (0.3 mg/kg) and non-drug (saline) states as interoceptive cues for operant discriminative stimulus conditions (SD and SΔ) as well as Pavlovian FP and FN for a light-CS, either leading to a shared food pellet outcome or non-outcome. Nicotine and saline sessions were intermixed. For one group of rats (n = 8), nicotine served as an SD for lever pressing (variable interval 60 s) and simultaneously functioned as an FN for CS-light→noUS relation on the same sessions. On intermixed sessions, saline served as the SΔ for lever pressing (non-reinforced) and FP, during which the 8-sec light preceded delivery of the food pellet (variable time ITI = 60 s). For the other group (n = 8) nicotine served as the SΔ (lever pressing non-reinforced) and FP for the CS, with saline serving in the reverse roles. Consecutive brief non-reinforcement tests revealed that: A) rates of lever pressing were significantly greater in SD than SΔ with nicotine and saline suggesting strong operant discriminative stimulus control; B) FP responding to the light CS with nicotine and saline was evident; and C) FN suppression of the CR with nicotine was not evident but weak under saline. These data suggest that nicotine can function as an interoceptive context that hierarchically can enter into concurrently opposing modulatory relations in Pavlovian and operant drug discrimination procedures.