Approach and escape to conspecific odors of reward and nonreward in rats

A three-compartment box was used, and a reward odor, or nonreward (extinction) odor, produced by another rat, was present in the middle compartment. Two control odor procedures were also used. The results showed that rats will approach a location in which another rat has previously been given reward more rapidly than they will escape from that location, but showed the opposite effect when the odor was produced by a rat undergoing extinction. The mere presence of an odor associated with another rat had the effect of producing much slower locomotion as compared to a no-odor control condition.     

Further evidence that Norway rats do not socially transmit learned aversions to toxic baits

Three experiments were undertaken to examine the effects of interactions with demonstrator rats made ill by injection of lithium chloride (LiCl) on the later food choices of their observers. We found that (1) observer rats that had been taught an aversion to an unfamiliar diet exhibited a substantial reduction of that aversion after interacting with poisoned demonstrators that had eaten the diet to which the observers had learned an aversion, (2) exposure of an observer rat to poisoned demonstrator rats that had eaten a diet interfered with later acquisition by the observer of an aversion to the diet that the poisoned demonstrators had eaten, and (3) after interacting with poisoned demonstrators that had eaten one of two diets, observers that ate both diets and were then made ill formed an aversion to whichever diet their respective, poisoned demonstrators had not eaten. The present experiments, like previous studies both in our laboratory and elsewhere, failed to provide any evidence that naive observer rats will learn to avoid a food as a result of interacting with demonstrator rats that had eaten the food and exhibit symptoms of toxicosis. To the contrary, observer rats in the present experiments exhibited an enhanced preference for foods eaten by sick demonstrators.     

Taste aversion learning and schedule-induced polydipsia in rats

Experiment 1 sought to determine whether schedule-induced drinking could be abolished by means of a taste aversion. Polydipsic rats were given access to a .4% saccharin solution while they were exposed to an intermittent food schedule. Immediately after the session, they received an intraperitoneal injection of either lithium chloride or sodium chloride. Following a recovery day with water in the experimental chamber, the animals were again exposed to the saccharin solution. The poisoned animals (lithium chloride) drank very little saccharin compared to the control animals (sodium chloride), indicating that they had learned a taste aversion in only one conditioning trial. Experiment 2 established that polydipsic rats can learn a taste aversion despite a long delay between schedule-induced saccharin consumption and poisoning, and that the delay gradient displayed by polydipsic rats is similar to that observed in thirst-motivated rats.     

Odors of individuality originating from the major histocompatibility complex are masked by diet cues in the urine of rats

Male Long-Evans rats were trained to discriminate between the urine odors of two congenic strains of rats (PVG and PVG.R1) in an olfactometer on a go/no-go operant task with water reinforcement. These odor donors differ genetically at only one locus of the major histocompatibility complex (MHC). The ability of the subjects to transfer their training to discriminate between novel individuals of the same MHC strain on the same and different diets was then examined. The subjects correctly generalized their original training to new samples from previously undiscriminated individuals of the same MHC type on the same diet without a significant drop in performance. A change in diet disrupted the perception of the MHC-related odor. In a second experiment, rats were trained to discriminate between the odors of pairs of genetically identical PVG or PVG.R1 rats on different diets and were tested for generalization using the odors of rats of the other strain (PVG.R1 or PVG) maintained on the same diet. Changing the strain of the odor donor did not disrupt the learned discrimination. The results of these two experiments confirm the ability of the MHC to generate constant cues in the urine but also reveal that variable diet cues disrupt the perception of these cues. The relationship between the MHC, diet, and other factors in determining individual odors is discussed.     

The role of experimenter-odor cues in the performance of object-memory tasks by rats

Two experiments assessed whether odors left on stimulus objects by experimenters who handle them might confound the interpretation of ostensibly visually guided object-memory tasks for rats. In Experiment 1, rats were able to discriminate the relative recency with which an experimenter touched two otherwise identical objects (intertouch interval = 4 sec), presumably on the basis of an odorintensity discrimination. However, after the rats mastered the odor discrimination with no delay between when the second of the two stimulus objects was last touched by the experimenter and when the rats were permitted to attempt the discrimination, their performance dropped to chance levels when this delay was increased to 15 sec. In Experiment 2, rats were trained in two slightly different ways to perform a delayed-nonmatching-to-sample (DNMS) task, one that involved systematic differences in the temporal order in which the experimenter handled the sample and novel stimulus objects and one that did not. There were no significant differences in the rate at which rats mastered the DNMS task with these two procedures, and the performance of rats that were trained according to the former procedure was unaffected when they were switched to the latter procedure. Moreover, rats required considerably fewer trials to master the DNMS task than the rats in Experiment 1 required to master the odor discrimination. These findings demonstrate that, under certain circumstances, rats can discriminate the relative recency with which two objects are handled by an experimenter, but that this ability contributes little to their performance of conventional object-based DNMS tasks.     

The effects of conditioned taste aversions on the acquisition and maintenance of schedule-induced polydipsia

Conditioned taste aversions produced a moderate, but transient, suppression of schedule-induced polydipsia. This suppression was greater and longer lasting when rats were offered a choice between water and the previously poisoned solution on the polydipsia baseline. A final experiment demonstrated that taste aversions were more effective in suppressing schedule-induced consumption when superimposed on a developing schedule-induced drinking baseline as opposed to a stable pattern of schedule-induced drinking. It was suggested that schedule-induced polydipsia is insensitive to conditioned taste aversions. This conclusion was discussed in terms of schedule-induced alcohol consumption and its potential as an animal model of alcoholism.     

Lack of reacquisition in learned taste aversions

Following ingestion of either water (Experiment 1) or saccharin (Experiment 2), experimental groups of rats were poisoned with lithium chloride and acquired an aversion to the ingested fluid. This aversion gradually extinguished and, in both experiments, was not reacquired when fluid intake was again followed by poisoning. These results are in marked contrast to usual findings of very rapid relearning following extinction with conditioning preparations other than taste-aversion learning.     

Radial localization of odors by human newborns.

To study sensitivity to radial location of an odor source, 20 human newborns, ranging from 16 to 130 hours of age, were presented with a small amount of ammonium hydroxide. The odor source was placed near the nose slightly to the left or right of midline, with its position randomized over repeated trails. Direction of headturn with respect to the odor location and diffuse motor activity were scored from the videotape recordings of the newborns' behavior. It was found that as a group, the newborns turned away from the odor source more frequently than they turned toward it. The tendency to turn away from the odor was stronger in infants who displayed less motor activity after the response. Newborns also exhibited a right bias in the direction of the head movements. It is concluded that a spatially appropriate avoidance response is present in the neonate and that the newborn is innately sensitive to the radial location of an odor.     

Taste + odor interactions in compound aversion conditioning

In three experiments with rats, taste + odor interactions in compound aversion conditioning were investigated. In Experiment 1, two odors (0.02% almond and 0.02% orange) were compared on single-element odor aversions, taste (denatonium) potentiated odor aversions, and potentiated odor aversions following taste extinction. Although no odor differences were seen following single-element conditioning, both types of potentiated orange odor aversions were stronger than their almond odor counterparts. These data show that odors of similar conditionability are differentially potentiated by the same taste. To determine whether these differences were due to unique perceptual representations, the effects of elemental extinction or compound extinction on aversions to the compound were investigated in Experiments 2 and 3. In Experiment 2, orange odor extinction weakened responding to the compound significantly more than taste extinction did. In contrast, almond odor extinction and taste extinction produced similar decrements in responding to the compound in Experiment 3. These results suggest that the perceptual representation of these specific taste + odor compounds are different, and they are discussed in regard to configural and within-compound association accounts of potentiation.     

Induction of odor preference in a specialist insect parasitoid

This paper deals with the effect of associative and nonassociative odor conditioning on odor preference in a specialist larval parasitic wasp ofDrosophila melanogaster, Leptopilina boulardi. Differently experienced females were offered a choice between banana and strawberry odors in a four-armed olfactometer. Wasps that were allowed to oviposit in an odorless airflow before testing exhibited no significant response to the odors, whereas females with an oviposition experience in the presence of an odor clearly preferred the scent that they had experienced. Furthermore, exposure to strawberry odor after oviposition could also induce a preference for strawberry or banana odor, depending on the concentrations of both scents used for conditioning and testing. This effect was independent of the time elapsed between oviposition and strawberry exposure, suggesting that it was caused by nonassociative conditioning and not by backward associative learning. Exposure to banana odor after oviposition had no effect on females’ responses. Variations in odor concentrations also influenced the expression of associative learning, although to a much lesser extent.     

Reinstatement of fear to an extinguished conditioned context

Rats were shocked in the black but not the white compartment of a shuttlebox and then exposed to the black compartment in the absence of the shock unconditioned stimulus (US) to extinguish fear responses (passive avoidance). In five experiments, rats were then shocked in a reinstatement context (distinctively different from the shuttlebox) to determine the conditions that reinstate extinguished fear responding to the black compartment. Rats shocked immediately upon exposure to the reinstatement chamber failed to show either reinstatement of avoidance of the black compartment or fear responses (freezing) when tested in the reinstatement chamber. In contrast, rats shocked 30 sec after exposure to the reinstatement chamber exhibited both reinstatement of avoidance of the black compartment and freezing responses in the reinstatement chamber (Experiment 1). Rats shocked after 30 sec of exposure to the reinstatement chamber but then exposed to that chamber in the absence of shock failed to exhibit reinstatement of the avoidance response and did not freeze when tested in the reinstatement chamber (Experiment 2). Rats exposed to a signaled shock in the reinstatement chamber and then exposed to that chamber in the absence of shock also failed to exhibit reinstatement of the avoidance response (Experiment 5). These rats showed fear responses to the signal but not to the reinstatement chamber. Finally, rats exposed for some time (20 min) to the reinstatement chamber before shock exhibited reinstatement of the avoidance response but failed to freeze when tested in the reinstatement chamber (Experiments 3 and 4). These results are discussed in terms of the contextual conditioning (Bouton, 1994) and the US representation (Rescorla, 1979) accounts of postextinction reinstatement.     

Flavor aversions and deprivation state

In the first four experiments, it was found that aversions to saccharin solution produced by contingent poisoning were similar regardless of whether the rats had been trained under the test deprivation or under a different deprivation; the two deprivation states used were thirst and satiety. In Experiment 5, rats were poisoned after drinking grape juice while hungry or poisoned after drinking milk while thirsty, but they were not poisoned after grape-thirst or milk-hunger combinations. In abstract terms, poisoning occurred after AX and BY stimulus combinations, but did not occur after AY and BX combinations. There was some learning under these discrimination conditions.     

Taste potentiates color-sickness associations in pigeons and quail

The present experiments assessed cue utilization in pigeons and quail on similar tests of poison-based aversion learning. In Experiments 1 and 2, three groups of pigeons were given colored water, flavored water, or colored flavored water prior to induction of sickness; these experiments differed only as to the specific colors and flavors used as stimuli. In both experiments, the birds trained with flavored water exhibited reliable taste aversions when tested with uncolored flavored water. Similar degrees of aversion were observed whether the flavored water had been colored or uncolored during training, suggesting that the color cue had little or no effect on the conditioning of the flavor cue. In contrast, the flavor cue had a pronounced effect on the conditioning of the color cue. When tested with unflavored colored water, the birds trained with colored flavored water exhibited significantly stronger color aversions than those trained with unflavored colored water. That is, the flavor cue enhanced or potentiated the conditioning of the color cue. In a third experiment, quail were trained in the same way as the pigeons with virtually the same result. The pattern of cue utilization observed in the present experiments with pigeons and quail differs markedly from that proposed by Wilcoxon, Dragoin, and Kral (1971) for quail. However, a reexamination of the results obtained by Wilcoxon et al. suggested that they are susceptible to an alternative interpretation consistent with the present results.     

Aversive conditioning of naturally produced reward and nonreward odors in rats

Past experiments have reported that rats encountering reward (R) or nonreward (N) goal events emit odors that can be utilized as discriminative stimuli for instrumental behavior by conspecifics. In the present study, thirsty male rats were aversively conditioned by ingestional toxicosis to R and N odors, and their suppression of water consumption in the presence of these odors was measured. Thirsty trained donors were placed into chambers containing R or N goal events to generate, respectively, the R or N odors. Test animals were given eight differential conditioning trials (four with one odor as CS+; four with the other as CS?), involving placement into an odorcontaining chamber with water available, followed by a LiCl injection on CS+ trials. Animals tested in their CS+ odor consumed significantly less water than did CS? and control subjects. Both R and N odors were conditioned by aversive means and readily discriminable from each other. This represents the first laboratory demonstration of aversive conditioning of such naturally produced odors, and it suggests that aversive conditioning may be useful in the study of odorous emissions generally. Implications for innate meanings of R and N odors are discussed.     

Poison avoidance and patch (location) selection in rats

Thirsty rats were tested on a four-armed radial maze with three water locations and one distinctive taste location (saccharin). Rats that were injected with lithium chloride after drinking a novel saccharin solution visited the saccharin location less than did unpoisoned animals, primarily during the later portions of the test sessions. When saccharin was moved to a different location, previously poisoned rats rapidly avoided the new saccharin location and increased visits to the original saccharin location, now rebaited with water. A similar pattern of learned avoidance and approach was obtained in Experiment 2 with three water locations and one vacant location (no water). These results indicate that: (1) sampling the contents of alternative patches mediates both learning to avoid the location of an aversive substance and returning to a newly viable patch, and (2) avoiding the location of a novel substance after a single poisoning occurs because the location does not contain an edible substance, not because of an aversion conditioned to environmental cues.     

Socially induced diet preference can partially reverse a LiCl-induced diet aversion

I examined the capacity of a socially induced enhanced diet preference to reverse the effects of a LiCl-induced diet aversion. I found that rats poisoned after eating a novel diet (Diet NPT) would consume substantial amounts of Diet NPT following interaction with a conspecific that had eaten Diet NPT. Neither rats interacting with a conspecific fed some other diet nor rats exposed to Diet NPT itself exhibited reduced aversion to Diet NPT. This surprising capacity of social interaction to ameliorate even profound toxicosis-induced aversions suggests that social influence may be a major experiential determinant of the diet preferences of free-living rats.     

A reexamination of the effects of motivational state on utilization of conspecific odors in the rat

Two previous studies suggested that rats are unable to use conspecifics’ odors when the motivational state of the donor rats is different from their own (Davis et al., 1974; Davis, Prytula, Noble, & Mollenhour, 1976). The effects of motivational conditions on the utilization of such odors were further evaluated in the present study. In Phase 1, test rats were given training either with donors in the same motivational state or with donors in a different state. Differential responses to donors’ odor emissions occurred only when the motivational states of donors and test subjects were the same, thus confirming earlier findings. However, when test subjects’ motivational conditions were changed in Phase 2, discriminations that had been present in Phase 1 were maintained even though the motivational states of these test subjects and their respective donors no longer matched. Thus, any constraint on the rat’s ability to use odors from conspecifics in a different motivational state is not absolute.     

The poisoned partner effect in rats: Some parametric considerations

Five experiments are reported establishing the poisoned partner effect (PPE) in rats as a robust phenomenon and indicating some of the factors that control its occurrence. Experiment 1 was a replication of Lavin, Freise, and Coombes (1980) and demonstrated that the PPE could be obtained under the conditions they described. Experiment 2 established that the PPE was not due to sensitization. Experiment 3 indicated that the nonpoisoned partner (NPP) had to be familiar with its poisoned partner in order for the PPE to be observed. Experiment 4 established that, under the conditions employed here, the NPP and its sick partner had to be paired together for at least 30 min following poisoning of the latter for the PPE to occur. Finally, Experiment 5 demonstrated that the NPP and its poisoned partner had to be paired together immediately following the poisoning episode. If 40 min or more was allowed to elapse following poisoning before the two were placed together, the PPE was attenuated. Taken together, these results indicate that the time course of the PPE is similar to that of the effects of the poisoning agent and suggest that some stimulus secreted by the poisoned rat and associated with the administration of the poison is the causative factor in the PPE.     

Effect of taste preexposure on taste and odor aversions

Thirsty Sprague-Dawley rats drank flavored water in a wind tunnel prior to lithium-induced toxicosis. Flavors were presented for 5 min; 30 min later a toxin, lithium chloride, was injected. After the rats had recovered, subsequent aversions to the taste and the odor were assessed separately. In Experiment 1, extensive preexposure to the taste component of the flavor attenuated neophobia to the flavor and the subsequent taste aversion. However, the subsequent odor aversion was unaffected. Experiment 2 partially replicated the results of Experiment 1 and showed that, in a situation in which only taste-potentiated odor aversions are usually found, nonpotentiated aversions were evident. Experiment 3 found that, in addition to attenuating taste aversions, taste preexposure enhances the capacity of rats to learn nonpotentiated odor aversions. The results are interpreted with a neural-based model of conditioned flavor aversions.     

Rats remember not wisely but too well

Rats were trained in a three-alternative spatial delayed matching-to-sample task in a starburst maze. Samples consisted of rewarded forced choices of one arm, and retention was indicated by rats’ returning to that arm after a 90-sec delay. If a rat made an error on its first choice, it was returned to the start compartment and allowed a second choice. Unlike in previous experiments with this task, all three arms were available during the animals’ second choices. The rats tended to perseverate in their second choices by returning to the arm that they had erroneously visited on their first choice. In Experiment 1, the accuracy of second choices following first-choice errors was below chance during the first block of sessions, when a 90-sec delay intervened between the first choice and the second choice, and at chance during the second block of sessions, when a short (5–6 see) delay intervened between first and second choices. In Experiment 2, long-delay and short-delay sessions were randomly presented to naive subjects. Similar results were obtained. In both experiments, the tendency to repeat the erroneous first choice was greater when long delays separated the two choices than when short delays were used. The results suggest that rats make their first-choice errors because they erroneously encode or remember the location of the sample and that they base their second choices on the same erroneous-memory. The increase in perseveration at long delays implies some kind of rehearsal-like mechanism that slows forgetting of the memory controlling the first choice.