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PubMed2004

The easy to hard effect and perceptual learning in flavor aversion conditioning.

In experiments on the easy to hard effect, pretraining on an easy discrimination results in better performance on a harder version of the discrimination than pretraining on the hard discrimination itself. In addition, some theories posit that unreinforccd preexposure to the easy discrimination should be as effective as differentially reinforced easy pretraining in producing the easy to hard effect. Two experiments on flavor aversion conditioning in rats demonstrated the basic easy to hard effect. However, in neither experiment was easy preexposure more effective than hard preexposure in enhancing learning of the hard discrimination. Indeed, in Experiment 2, rats preexposed to an easy discrimination learned the hard discrimination significantly more slowly than those preexposed to the hard discrimination itself.

Animals↗
PubMed2005

Recovery from blocking between outcomes.

Contemporary associative learning research largely focuses on cue competition phenomena that occur when 2 cues are paired with a common outcome. Little research has been conducted to investigate similar phenomena occurring when a single cue is trained with 2 outcomes. Three conditioned lick suppression experiments with rats assessed whether treatments known to alleviate blocking between cues would also attenuate blocking between outcomes. In Experiment 1, conditioned responding recovered from blocking between outcomes when a long retention interval was interposed between training and testing. Experiment 2 obtained recovery from blocking between outcomes when the blocking outcome was extinguished after the blocking treatment. In Experiment 3, a recovery from blocking between outcomes occurred when a reminder stimulus was presented in a novel context prior to testing. Collectively, these studies demonstrate that blocking of outcomes, like blocking of cues, appears to be caused by a deficit in the expression of an acquired association.

Analysis of Variance↗
PubMed2006

Associative activation of stimulus representations restores lost salience: implications for perceptual learning.

In 3 experiments, rats received preexposure to presentations of a compound flavor BX. The effective salience of B was then tested by assessing its ability to interfere with the aversion controlled by another flavor or the tendency to drink a saline solution after the induction of a salt need. It was found that the effective salience of B was maintained when during preexposure, presentations of BX alternated with presentations of X alone. This was true both when BX was presented as a simultaneous compound (Experiment 1) and as a serial compound (X-->B; Experiments 2 and 3); salience was not maintained when the serial compound took the form B-->X (Experiments 2 and 3a). It was argued that the salience of B declines during preexposure but is restored when presentations of X are able to activate the representation of B by way of the associative X-B link.

Animals↗
PubMed2006

A short intertrial interval facilitates acquisition of context-conditioned fear and a short retention interval facilitates its expression.

Rats were shocked in a context on two occasions and then tested for fear reactions as indexed by freezing. Rats spent the interval between conditioning trials and between conditioning and test in their home cages. A short interval between context-conditioning trials or between trials involving a discrete conditioned stimulus (CS) produced better learning than longer intervals. A short retention interval between conditioning and test produced better performance than longer intervals. The effects of the intertrial interval on learning are the opposite of those reported previously and are opposite to those predicted by contemporary learning theories. The effects of the training to test interval on performance are predicted by Wagner's sometimes opponent process (SOP) theory (Wagner, 1981).

Animals↗
PubMed2006

Inhibitory associations contribute to perceptual learning in humans.

Perceptual learning in humans was examined in 2 experiments. In Experiment 1, participants received intermixed exposure to 2 similar compounds (AX, BX, AX, BX, . . .) and blocked exposure to a 2nd pair of similar compounds (CY, CY, . . . , DY, DY, . . .). Aversions established to AX and CY generalized less to BX than to DY. In Experiment 2, 1 pair of compounds was presented in a forward order (i.e., AX3BX), whereas the 2nd pair of compounds was presented in a backward order (i.e., DY-->CY). Aversions established to AX and CY generalized less to BX than to DY. These results indicate that inhibitory associations contribute to perceptual learning in humans and thereby establish a fundamental similarity between the mechanisms that underlie perceptual learning in humans and rats.

Adolescent↗
PubMed2007

Stimulus-outcome interactions during instrumental discrimination learning by rats and humans.

The associative structure mediating goal-directed action was investigated using congruent and incongruent conditional discriminations. The stimulus was the same as the outcome in each component of the congruent discriminations, whereas the stimulus of one component of the incongruent discriminations was the same as the outcome of the other component. Humans, but not rats, learned the congruent discrimination more rapidly than the incongruent discrimination, a difference that the authors attribute to the fact that outcome-response associations caused response conflict in the incongruent discrimination. Moreover, responding was resistant to outcome devaluation following incongruent, but not congruent, training, suggesting that both humans and rats adopted a stimulus-response strategy to resolve the incongruent discrimination.

Adult↗
PubMed1990

Social transmission of food preferences in Japanese monkeys (Macaca fuscata) after mere exposure or aversion training.

In Experiment 1, 3 mother-child pairs of Japanese monkeys (Macaca fuscata) were given simultaneous choice tests between raisins and popcorn. The mothers and offspring showed different choice patterns. Cofeeding opportunities were then alternated with individual choice tests. In Experiment 2,2 other pairs were added. Each animal was again offered simultaneous choice tests between marshmallows and almonds. Food aversion conditioning was used to create different choice patterns for mothers and offspring. After cofeeding and choice tests, the differences in choice patterns disappeared in both experiments. The changes after contact with the other's eating pattern during cofeeding was as follows: foods consumed by either came to be eaten by both; foods consumed by both continued to be eaten by both; and foods consumed by neither continued to be ignored. The results provide evidence for social transmission of food preferences in this species.

Animals↗
PubMed1990

Spatial contiguity, not cue-to-consequence, is the issue in taste-potentiated noise-illness associations: comment on Holder, Bermudez-Rattoni, and Garcia (1988).

Holder, Bermudez-Rattoni, and Garcia (1988) allege to have failed to corroborate findings from our laboratory (Ellins, Cramer, & Whitmore, 1985; Ellins & von Kluge, 1987) that taste-potentiated noise-illness associations can be established under conditions of spatial contiguity. We maintain that Holder et al. have provided additional experimental support for our contention that spatial contiguity is an important factor in the taste-potentiation of nongustatory stimuli. In addition, we take issue with their conclusion that the results of our research are incompatible with the conditioning principle of cue-to-consequence.

Animals↗
PubMed2004

Testosterone's analgesic, anxiolytic, and cognitive-enhancing effects may be due in part to actions of its 5alpha-reduced metabolites in the hippocampus.

Although testosterone (T) may decrease anxiety and enhance cognitive performance, its mechanisms are not well understood. The authors hypothesized that if T's effects are mediated in part through actions of its 5alpha-reduced, nonaromatizable metabolite dihydrotestosterone (DHT) and/or its 3alpha-hydroxysteroid dehydrogenase reduced metabolite 3alpha-androstanediol (3alpha-diol) in the hippocampus, then T, DHT, and 3alpha-diol administration should produce similar behavioral effects concomitant with elevating T metabolites in the hippocampus. Gonadectomized male rats administered T, DHT, or 3alpha-diol via Silastic capsules or intrahippocampal infusions had greater analgesia (tail flick, paw lick), less anxiety behavior (plus-maze, open field, defensive freezing), and better learning (inhibitory avoidance) compared with vehicle control rats. Only 3alpha-diol levels in the hippocampus were consistently elevated in conjunction with these behavioral effects.

3-alpha-Hydroxysteroid Dehydrogenase (B-Specific)↗
PubMed2005

Genetic correlational analyses of ethanol reward and aversion phenotypes in short-term selected mouse lines bred for ethanol drinking or ethanol-induced conditioned taste aversion.

Short-term selective breeding created mouse lines divergent for ethanol drinking (high drinking short-term selected line [STDRHI], low drinking [STDRLO]) or ethanol-induced conditioned taste aversion (CTA; high [HTA], low [LTA]). Compared with STDRLO, STDRHI mice consumed more saccharin and less quinine, exhibited greater ethanol-induced conditioned place preference (CPP), and showed reduced ethanol stimulation and sensitization under some conditions; a line difference in ethanol-induced CTA was not consistently found. Compared with LTA, HTA mice consumed less ethanol but were similar in saccharin consumption, sensitivity to ethanol-induced CPP, and ethanol-induced locomotor stimulation and sensitization. These data suggest that ethanol drinking is genetically associated with several reward-and aversion-related traits. The interpretation of ethanol-induced CTA as more genetically distinct must be tempered by the inability to test the CTA lines beyond Selection Generation 2.

Alcohol Drinking↗
PubMed1976

Conditioned taste aversions and neophobia in rats with hippocampal lesions.

In the first experiment extensive hippocampal lesions retarded, but did not prohibit, the conditioning of a strong taste aversion to physiological saline (the conditioned stimulus; CS) when illness (the unconditioned stimulus; UCS) was induced by injecting rats with apomorphine 15 min following ingestion of the saline. In the second experiment hippocampal lesions reduced the aversiveness of novelty in a drinking fluid for the thirsty rat. It was suggested that the mild impairment of taste aversion learning in the rats with hippocampal lesions was not the result of destruction of mnemonic mechanisms that serve to span the long CS-UCS interval but rather that the reduced intensity of the aversion resulted from a lesion-altered neophobic disposition that weakened the saliency of the novel flavor CS.

Animals↗
PubMed1976

Effects of lesions of the gustatory necortex on taste aversion learning in the rat.

Normal rats and rats with lesions of the gustatory neocortex (GN) were compared for their ability to learn aversions to taste cues paired with toxicosis. When the taste presentation was followed immediately by toxicosis, normal rats and rats with lesions of the posterior (visual) neocortex learned aversions to sucrose, sodium chloride, quinine hydrochloride, and hydrochloric acid solutions. Rats with GN lesions learned aversions to all solutions except sucrose. In preference tests, all solutions were shown to be discriminable from water by both normal rats and rats with GN lesions. Under conditions in which a 6-hr delay separated taste presentation and toxicosis, normal rats again learned specific aversions to all four solutions, but rats with GN lesions failed to learn specific aversions to sucrose, sodium chloride, and hydrochloric acid solutions. It was shown that the ability of rats with GN lesions to learn aversions to sucrose and quinine depended on stimulus concentration; and it was proposed that the data could be accounted for by postulating a change in the threshold for taste-illness associations following GN lesions.

Animals↗
PubMed1978

Ingestional aversion learning in preweanling rats.

Ingestional aversions were conditioned in 12- and 15-day-old rats by infusing a .5% solution of saccharin into the oral cavity and following this oral infusion by the injection of lithium chloride. At both ages, subjects for which the saccharin exposure was followed by lithium injection within 2-3 min drank less when the saccharin solution was again presented by oral infusion 12 hr later; such suppressions of intake were not observed in subjects that previously received the saccharin and lithium in an unpaired fashion (Experiments 1 and 3). Ingestional aversions were also learned by 12-day-olds when a 30-min interval was introduced between saccharin exposure and lithium toxicosis but not when toxicosis was delayed by 120 min (Experiment 2). In contrast, 15-day-olds learned aversions with both the 30- and 120-min-delay intervals (Experiment 3). Despite the absence of long-delay learning in 12 day olds, ingestional aversions conditioned at 12 days of age were retained for 2 wk (Experiment 4). These results provide further evidence of the associative abilities of neonatal rats and illustrate a developmental aspect of long-delay learning.

Age Factors↗
PubMed1979

Taste aversions to mother's milk: the age-related role of nursing in acquisition and expression of a learned association.

The development of taste aversion learning to novel cues contained in mother's milk was examined in rat pups. Pups receiving distinctive mild by experimenter-delivered oral infusions followed by toxicosis formed an aversion to the dam's diet. Robust aversions were learned as early as Day 10 and were retained for at least 11 days. When the same distinctive milk was obtained directly from a foster mother through nursing, however, only weanling-age pups (over 20 days) formed an aversion. X-ray analysis of nipple location in the mouths of suckling pups suggested that pups between the ages of 10 and 21 days receive milk at a similar tongue locus. Flavored milk was then delivered at specific time intervals in controlled quantities through tongue cannulas implanted at loci corresponding to the nipple position shown by the X-rays. Cannulated preweanling pups that were attached to a nipple during milk delivery failed to associate the taste cue with illness, whereas both preweanlings off the nipple and weanlings on the nipple acquired aversions to the taste cue in the milk. The evidence obtained in these experiments suggests that pups of all ages are incapable of expressing a taste aversion in a nursing situation and that preweanling pups in particular are also dificient in acquiring aversions within a suckling context. The inability of preweanling pups to acquire taste aversions in a nursing situation appears to result from a failure to associate taste cues with illness rather than a failure to detect taste cues obtained from a nipple.

Age Factors↗