Within-compound associations are not sufficient to produce taste-mediated odor potentiation

Elemental and configural threat learning bias extinction generalization

Emotional experiences often contain a multitude of details that may be represented in memory as individual elements or integrated into a single representation. How details associated with a negative emotional event are represented in memory can have important implications for extinction strategies designed to reduce emotional responses. For example, is extinguishing one cue associated with an aversive outcome sufficient to reduce learned behavior to other cues present at the time of learning that were not directly extinguished? Here, we used a between-subjects multi-day threat conditioning and extinction task to assess whether participants generalize extinction from one cue to unextinguished cues. On Day 1, one group of participants learned that a compound conditioned stimulus, composed of a tone and colored square, predicted an uncomfortable shock to the wrist (Compound group). A second group learned that the tone and square separately predicted shock (Separate group). On Day 2, participants in both groups were exposed to the tone in the absence of shocks (cue extinction). On Day 3, we tested whether extinction generalized from the extinguished to the unextinguished cue, as well as to a compound composed of both cues. Results showed that configural and elemental learning had unique and opposite effects on extinction generalization. Subjects who initially learned that a compound cue predicted shock successfully generalized extinction learning from the tone to the square, but exhibited threat relapse to the compound cue. In contrast, subjects who initially learned that each cue individually predicted shock did not generalize extinction learning from the tone to the square, but threat responses to the compound were low. These results highlight the importance of whether details of an aversive event are represented as integrated or separated memories, as these representations affect the success or limits of extinction generalization.

The selectivity of aversive memory reconsolidation and extinction processes depends on the initial encoding of the Pavlovian association

In reconsolidation studies, memories are typically retrieved by an exposure to a single conditioned stimulus (CS). We have previously demonstrated that reconsolidation processes are CS-selective, suggesting that memories retrieved by the CS exposure are discrete and reconsolidate separately. Here, using a compound stimulus in which two distinct CSs are concomitantly paired with the same aversive unconditioned stimulus (US), we show in rats that reexposure to one of the components of the compound CS triggers extinction or reconsolidation of the other component. This suggests that the original training conditions play a critical role in memory retrieval and reconsolidation.

Evidence that the sweetness of odors depends on experience in rats

Humans describe their perception of certain odorants in terms of taste qualities (e.g., sweet). It has also been found that in humans, novel odorants can rapidly and irreversibly acquire a taste, even after just a single pairing with a taste. It remains unclear whether flavor objects in general, and odor-taste generalizations in particular, are experience-dependent. Interactions might result from a failure by humans to sufficiently analyze the olfactory and gustatory components of compound flavorants. Here, we tested odor-taste generalizations in rats with or without paired exposure to an odorant and a tastant. We evaluated the generalization of conditioned odor aversion to tastants by rats. Our findings suggest that rats behave toward putatively tasteless retronasal odorants as if they were sweet only after prior paired experience of the odorant with a sweet tastant. These data support the hypothesis that taste-like qualities of odors are learned and are not innate. Furthermore, the present results suggest that acquisition of a taste quality by an odor need not depend on higher cognitive abilities. This study helps to establish the rat as a model for the study of behavioral neuroscience of flavor.

Differences in taste-potentiated odor aversions with O+/OT+ versus OT+/O+ conditioning: Implications for configural associations

The present research demonstrates a conditioning order effect difference: Odor-aversion conditioning is stronger following OT+/O+ conditioning than following O+/OT+ conditioning with specific odor (O) and taste (T) cues. When a weak odor cue was used in Experiments 1A and 1B, OT+/O+ conditioning produced significantly stronger odor aversions than did either O+/OT+ or O+/O+ conditioning, which did not differ. The same design was used in Experiment 2 with a strong odor, but the order effect difference was not replicated, suggesting that the order effect difference is specific to conditions that produce taste-potentiated odor aversions. The interpretation that O+/OT+ conditioning is weaker because of the absence of a taste-odor within-compound association was not supported in Experiments 3 and 4. Notably, using stimuli that supported potentiation in earlier experiments, in Experiment 4, we found evidence of a taste-odor within-compound association in the absence of potentiation. These results confirm that previous theories of potentiation (within-compound association model, sensory-and-gate channeling model) are not sufficient to produce potentiation. Instead, these results are interpreted in terms of taste-odor configural associations.

An examination of the effectiveness of inflation and deflation treatments in detecting within-compound learning of a taste aversion

Two conditioned taste aversion experiments with rats assessed the relative effectiveness in providing evidence of within-compound learning of different procedures that involve the initial compound presentation of two stimuli, A and X, with the unconditioned stimulus (i.e., AX+). In Experiment 1, following a single AX+ trial, groups A+ and B+ received an additional conditioning trial (i.e., inflation treatment) with A and B, respectively, whereas group A- received an extinction trial (i.e., deflation treatment) with A. The results showed a reduction in the aversion elicited by the target stimulus, X, in group A- relative to both groups A+ and B+, which did not differ. Experiment 2 further investigated the failure of group A+ to increase the aversion to X relative to control group B+ by pairing A or B with either the same unconditioned stimulus that was previously paired with AX (groups A+ and B+) or with a stronger unconditioned stimulus (groups A* and B*). The results showed increased aversion to X in group A* relative to group B*, but not in group A+ relative to group B+. These results are interpreted as indicative of extinction of the within-compound association during the treatment with A, which could likely impair the detection of within-compound learning following an inflation, but not a deflation treatment.