Context dependency of conditioned aversions to water and sweet tastes

Instrumental and Pavlovian Mechanisms in Alcohol Use Disorder

Purpose of Review

Current theories of alcohol use disorders (AUD) highlight the importance of Pavlovian and instrumental learning processes mainly based on preclinical animal studies. Here, we summarize available evidence for alterations of those processes in human participants with AUD with a focus on habitual versus goal-directed instrumental learning, Pavlovian conditioning, and Pavlovian-to-instrumental transfer (PIT) paradigms.

Recent Findings

The balance between habitual and goal-directed control in AUD participants has been studied using outcome devaluation or sequential decision-making procedures, which have found some evidence of reduced goal-directed/model-based control, but little evidence for stronger habitual responding. The employed Pavlovian learning and PIT paradigms have shown considerable differences regarding experimental procedures, e.g., alcohol-related or conventional reinforcers or stimuli.

Summary

While studies of basic learning processes in human participants with AUD support a role of Pavlovian and instrumental learning mechanisms in the development and maintenance of drug addiction, current studies are characterized by large variability regarding methodology, sample characteristics, and results, and translation from animal paradigms to human research remains challenging. Longitudinal approaches with reliable and ecologically valid paradigms of Pavlovian and instrumental processes, including alcohol-related cues and outcomes, are warranted and should be combined with state-of-the-art imaging techniques, computational approaches, and ecological momentary assessment methods.

Habitual Preference for the Nondrug Reward in a Drug Choice Setting

For adaptive and efficient decision making, it must be possible to select between habitual alternative courses of action. However, research in rodents suggests that, even in the context of simple decision-making, choice behavior remains goal-directed. In contrast, we recently found that during discrete trial choice between cocaine and water, water-restricted rats preferred water and this preference was habitual and inflexible (i.e., resistant to water devaluation by satiation). Here we sought to test the reproducibility and generality of this surprising finding by assessing habitual control of preference for saccharin over cocaine in non-restricted rats. Specifically, after the acquisition of preference for saccharin, saccharin was devalued and concurrent responding for both options was measured under extinction. As expected, rats responded more for saccharin than for cocaine during extinction, but this difference was unaffected by saccharin devaluation. Together with our previous research, this result indicates that preference for nondrug alternatives over cocaine is under habitual control, even under conditions that normally support goal-directed control of choice between nondrug options. The possible reasons for this difference are discussed.

Effects of Limited and Extended Pavlovian Training on Devaluation Sensitivity of Sign- and Goal-Tracking Rats

Individual differences in Pavlovian approach predict differences in devaluation sensitivity. Recent studies indicate goal-tracking (GT) rats are sensitive to outcome devaluation while sign-tracking (ST) rats are not. With extended training in Pavlovian lever autoshaping (PLA), GT rats display more lever-directed behavior, typical of ST rats, suggesting they may become insensitive to devaluation with more Pavlovian training experience. Here, we use a within-subject satiety-induced outcome devaluation procedure to test devaluation sensitivity after limited and extended PLA training in GT and ST rats. We trained rats in PLA to determine GT and ST groups. Then, we sated rats on either the training pellets (devalued condition) or homecage chow (valued condition) prior to brief non-reinforced test sessions after limited (sessions 5/6) and extended (sessions 17/18) PLA training. GT rats decreased conditioned responding under devalued relative to valued conditions after both limited and extended training, demonstrating they are sensitive to satiety devaluation regardless of the amount of PLA training. While ST rats were insensitive to satiety devaluation after limited training, their lever directed behavior became devaluation sensitive after extended training. To determine whether sign-tracking rats also displayed sensitivity to illness-induced outcome devaluation after extended training, we trained a separate cohort of rats in extended PLA and devalued the outcome with lithium chloride injections after pellet consumption in the homecage. ST rats failed to decrease conditioned responding after illness-induced outcome devaluation, while Non-ST rats (GT and intermediates) were sensitive to illness-induced outcome devaluation after extended training. Together, our results confirm devaluation sensitivity is stable in GT rats across training and devaluation approaches. Extended training unmasks devaluation sensitivity in ST rats after satiety, but not illness-induced devaluation, suggesting ST rats respond appropriately by decreasing responding to cues during state-dependent but not inference-based devaluation. The differences in behavioral flexibility across tracking groups and devaluation paradigms have translational relevance for the understanding state- vs. inference-based reward devaluation as it pertains to drug addiction vulnerability.

Circadian-temporal context and latent inhibition of conditioned taste aversion: Effect of restriction in the intake of the conditioned taste stimulus

Latent inhibition of conditioned taste aversion (CTA) is sensitive to changes in the temporal context. A change in the time of day of conditioning with respect to the time of day of the preexposure can disrupt the latent inhibition. This contextual change in the time of day may reveal a temporal specificity of latent inhibition. The optimum procedure to induce this temporal specificity is not well established. For example, it has been shown that a long period of habituation to temporal contexts is one factor that can determine the effect. However, the experimental conditions on the conditioning day that facilitate this phenomenon are unknown. The aim of this study is to elucidate whether a restriction in the intake of the conditioned taste stimulus affects the temporal specificity of latent inhibition. Two main groups of Wistar rats were tested in a latent inhibition of CTA paradigm, in which the temporal specificity of this phenomenon was analyzed by a change in the time of day of conditioning. The intake of the taste stimulus was restricted in the conditioning day in one of the groups, but this restriction was not applied in the other group. The results indicated temporal specificity of latent inhibition only in the group without restriction, but not in the group with limitation in the intake of the taste stimulus during conditioning. These findings can help to elucidate the characteristics of the procedure to induce temporal specificity of latent inhibition.

Evidence of structure and persistence in motivational attraction to serial Pavlovian cues

Sign-tracking is a form of autoshaping where animals develop conditioned responding directed toward stimuli predictive of an outcome even though the outcome is not contingent on the animal's behavior. Sign-tracking behaviors are thought to arise out of the attribution of incentive salience (i.e., motivational value) to reward-predictive cues. It is not known how incentive salience would be attributed to serially occurring cues, despite cues often occurring in a sequence in the real world as reward approaches. The experiments presented here demonstrate that reward-proximal cue responding is not altered by the presence of a distal reward cue (Experiment 1), and similarly that reward-distal cue responding which animals favor, is not altered by the presence of a reward-proximal cue (Experiment 2). Extinction of reward-proximal cues after training of the serial sequence leads to a generalized reduction in lever responding (Experiment 3). Together, we show that both Pavlovian serial lever cues acquire motivational value. These experiments also provide support to the notion that sign-tracking responses are insensitive to changes in outcome value, and that responding to serial cues creates a distinct context for outcome value.

Acquisition and retention of conditioned aversions to context and taste in laboratory mice

We compared the rate of acquisition and strength of retention of conditioned context aversion (CCA) with conditioned taste aversion (CTA) using pigmented, genetically heterogeneous mice (derived from Large and Small strains). Extending previous findings, in Experiment 1, mice accustomed to drinking from large glass bottles in the colony room learned to avoid graduated tubes after a single conditioning trial when drinking from these novel tubes was paired with injections of LiCl. The results also showed that CCA could be developed even when there was a 30-minute delay between conditioned stimulus and unconditioned stimulus. Retention of the aversion lasted for 4 weeks in both Immediate and Delay groups. Studies of conditioned saccharin aversion were conducted in Experiment 2. CTA acquisition was very similar to that observed in CCA and duration of aversion retention was similar in the CCA and CTA Delay groups, although at least 2 weeks longer in the Immediate group. Thus, CCA acquisition and retention characteristics are closer to those seen for CTA than has previously been reported. In Experiment 3, we examined whether albino mice (which are known to have weaker visual abilities compared to pigmented mice) would develop CCA comparable to those of pigmented mice. The development of conditioned aversion and its duration of retention was similar in albinos and pigmented mice. Nonspecific aversion emerged as an important contributor to strength of aversion during retention trials in both CCA and CTA paradigms with pigmented (but not albino) mice and deserves additional scrutiny in this field of inquiry.

Nonreinforced flavor exposure attenuates the effects of conditioned taste aversion on both flavor consumption and cue palatability

Nonreinforced exposure to a cue tends to attenuate subsequent conditioning with that cue-an effect referred to as latent inhibition (LI). In the two experiments reported here, we examined LI effects in the context of conditioned taste aversion by examining both the amount of consumption and the microstructure of the consummatory behavior (in terms of the mean size of lick clusters). The latter measure can be taken to reflect affective responses to, or the palatability of, the solution being consumed. In both experiments, exposure to a to-be-conditioned flavor prior to pairing the flavor with nausea produced by lithium chloride attenuated both the reduction in consumption and the reduction in lick cluster sizes typically produced by taste aversion learning. In addition, we observed a tendency (especially in the lick cluster measure) for nonreinforced exposure to reduce neophobic responses to the test flavors. Taken together, these results reinforce the suggestion from previous experiments using taste reactivity methods that LI attenuates the effects of taste aversion on both consumption and cue palatability. The present results also support the suggestion that the failure in previous studies to see concurrent LI effects on consumption and palatability was due to a context specificity produced by the oral taste infusion methods required for taste reactivity analyses. Finally, the fact that the pattern of extinction of conditioned changes in consumption and in lick cluster sizes was not affected by preexposure to the cue flavors suggests that LI influenced the quantity but not the quality of conditioned taste aversion.

The entorhinal cortex is involved in conditioned odor and context aversions

In a natural environment, avoidance of a particular food source is mostly determined by a previous intake experience during which sensory stimuli such as food odor, become aversive through a simple associative conditioned learning. Conditioned odor aversion learning (COA) is a food conditioning paradigm that results from the association between a tasteless scented solution (conditioned stimulus, CS) and a gastric malaise (unconditioned stimulus, US) that followed its ingestion. In the present experimental conditions, acquisition of COA also led to acquisition of aversion toward the context in which the CS was presented (conditioned context aversion, CCA). Previous data have shown that the entorhinal cortex (EC) is involved in the memory processes underlying COA acquisition and context fear conditioning, but whether EC lesion modulates CCA acquisition has never be investigated. To this aim, male Long-Evans rats with bilateral EC lesion received CS-US pairings in a particular context with different interstimulus intervals (ISI). The results showed that the establishment of COA with long ISI obtained in EC-lesioned rats is associated with altered CCA learning. Since ISI has been suggested to be the determining factor in the odor- and context-US association, our results show that the EC is involved in the processes that control both associations relative to ISI duration.

Eyeblink classical conditioning and post-traumatic stress disorder - a model systems approach

Not everyone exposed to trauma suffers flashbacks, bad dreams, numbing, fear, anxiety, sleeplessness, hyper-vigilance, hyperarousal, or an inability to cope, but those who do may suffer from post-traumatic stress disorder (PTSD). PTSD is a major physical and mental health problem for military personnel and civilians exposed to trauma. There is still debate about the incidence and prevalence of PTSD especially among the military, but for those who are diagnosed, behavioral therapy and drug treatment strategies have proven to be less than effective. A number of these treatment strategies are based on rodent fear conditioning research and are capable of treating only some of the symptoms because the extinction of fear does not deal with the various forms of hyper-vigilance and hyperarousal experienced by people with PTSD. To help address this problem, we have developed a preclinical eyeblink classical conditioning model of PTSD in which conditioning and hyperarousal can both be extinguished. We review this model and discuss findings showing that unpaired stimulus presentations can be effective in reducing levels of conditioning and hyperarousal even when unconditioned stimulus intensity is reduced to the point where it is barely capable of eliciting a response. These procedures have direct implications for the treatment of PTSD and could be implemented in a virtual reality environment.

Conditioning-specific reflex modification of the rabbit (Oryctolagus cuniculus) nictitating membrane response is sensitive to context

Conditioning-specific reflex modification occurs when an unconditioned response is modified in the absence of the conditioned stimulus as a result of pairings of the conditioned stimulus and an unconditioned stimulus. In two experiments, we assessed conditioning-specific reflex modification in either a novel context (Experiment 1) or a context different from, but equally familiar in relation to, the training context (Experiment 2). Conditioning-specific reflex modification did not demonstrate sensitivity to a novel context but did demonstrate sensitivity to a change in familiar context. The data cannot be explained by unconditioned stimulus preexposure, overtraining, or context insensitivity. The results suggest that conditioning-specific reflex modification models normal stress and may be used to evaluate theories of and treatments for posttraumatic stress disorder.