Contextual effects in conditioning, latent inhibition, and habituation: Associative and retrieval functions of contextual cues.

Rats were used as subjects in four experiments to investigate the transfer of learning from one context to another. Subjects received two sessions of training each day, one in each of two different contexts. Experiment 1 showed that the habituation of the unconditioned response to a stimulus presented in one context was left intact when the stimulus was presented in another context, but that latent inhibition was attenuated when preexposure and conditioning phases occurred in different contexts. Experiments 2 and 3 demonstrated that a conditioned response made on the basis of an appetitive reinforcer was diminished when conditioning and testing occurred in different contexts, but that aversive conditioning was not influenced by the context in which testing occurred. In Experiment 4, the presence of an aversive reinforcer during training did not preclude the occurrence of context-specific conditioning on the basis of an appetitive reinforcer. Associative and retrieval-based interpretations of the results are explored. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Cigarette smoking predicts development of depressive symptoms among U.S. adolescents

Latent inhibition (LI) refers to retarded conditioning to a stimulus as a consequence of its nonreinforced preexposure. LI is impaired in acute schizophrenic patients and in rats treated with amphetamine. Neuroleptic drugs enhance LI, and this effect is selective and specific for this class of drugs. The present experiments tested the proposition that neuroleptic-induced enhancement of LI stems from decreased capacity of stimulus-preexposed animals to switch responding according to the new stimulus-reinforcement contingency in the conditioning stage. LI was assessed using an off-baseline conditioned emotional response (CER) procedure in rats licking for water, consisting of three stages: preexposure to the-to-be conditioned stimulus, tone; conditioning, in which the preexposed stimulus was paired with a foot-shock; and test, in which LI was indexed by animals' degree of suppression of licking during tone presentation. Whereas in previous studies that demonstrated LI enhancement by neuroleptics, preexposure consisted of 10 to 40 tones, and conditioning included two tone-shock pairings, the present experiments used 40 tone preexposures, followed by an extended conditioning stage with five tone-shock pairings. It was expected that under these conditions no LI effect would be evident in untreated animals, but that animals treated with a neuroleptic drug, either during the entire LI procedure or only in conditioning, would show LI. Experiments 1 and 2 showed that LI was obtained in rats treated with haloperidol (0.1 mg/kg in experiment 1, 0.03 and 0.2 mg/kg in experiment 2) but not in the untreated controls. Experiment 3 showed that the same outcome was obtained when haloperidol (0.1 mg/kg) administration was confined to the conditioning stage. Experiment 4 showed that clozapine (5 mg/kg)-treated animals showed LI when the drug was confined to conditioning, but not to the preexposure stage. The implications of these results for the mechanism of action of neuroleptic drugs are discussed.     

Additional evidence for intact appetitive trace conditioning in hippocampal-lesioned rats.

Hippocampal lesions impair aversive trace conditioning but do not interfere with appetitive Pavlovian trace conditioning of the licking response (LR). This experiment examined whether learning to discriminate the events occurring in the home cage and in the training chamber could account for the differential effects of hippocampal lesions on aversive and appetitive trace conditioning. Performance of rats with excitotoxic lesions of the hippocampus was compared to that of sham-operated rats in LR trace conditioning. The unconditional stimulus (US) “cola soft drink” was delivered only in the training chamber. Thus, as in aversive conditioning procedures, the hedonic properties of the US and the resulting behaviors and motivational states occurred only in that environment. The results failed to reveal learning differences between lesioned rats and controls. Our findings and those of other reports concur that trace conditioning with an appetitive US is independent of the hippocampal system. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Potentiation of latent inhibition.

Rats were given exposure either to an odor (almond) or a compound of odor plus taste (almond plus saline), prior to training in which the odor served as the conditioned stimulus. It was found, for both appetitive and aversive procedures, that conditioning was retarded by preexposure (a latent inhibition effect), and the extent of the retardation was greater in rats preexposed to the compound (i.e., latent inhibition to the odor was potentiated by the presence of the taste). In contrast, the presence of the taste during conditioning itself overshadowed learning about the odor. We argue that the presence of the salient taste in compound with the odor enhances the rate of associative learning, producing a rapid loss in the associability of the odor. This loss of associability will generate both overshadowing and the potentiation of latent inhibition that is observed after preexposure to the compound. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Latent inhibition experiments with goldfish (Carassius auratus).

Examined evidence of latent inhibition in a series of experiments with goldfish. In Exp I, 12 Ss were given nonreinforced preexposure to a color that subsequently predicted shock in an activity conditioning situation; their performance did not differ from that of 12 control Ss preexposed to a markedly different color. In Exp II, 12 Ss given nonreinforced preexposure to a tone and an unstimulated control group of 12 Ss were trained in an appetitive situation, with the tone serving either as a conditioned excitor or as a conditioned inhibitor. Preexposure had significant effect in the conditioned excitation training, but it reduced the level of responding both to the positive stimulus and to the negative compound in the conditioned inhibition training. In Exps III and IV, classical aversive conditioning was studied in the shuttle box. In Exp III, excitatory conditioning to a color was found to be impaired (relative to the performance of nonpreexposed control Ss) as much by nonreinforced preexposure to the training color as by nonreinforced preexposure to a markedly different color; substantial variation in amount of preexposure was without significant effect. In the conditioned inhibition training of Exp IV, 12 Ss with nonreinforced preexposure responded less than did 12 unstimulated control Ss, both to the positive stimulus and to the negative compound. Results demonstrate that the effect of preexposure on goldfish is their reduction of general responsiveness or level of arousal. (47 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Identification of types II, IX and X collagens at the insertion site of the bovine achilles tendon

The authors provide initial documentation that juvenile rats emit short, high-frequency ultrasonic vocalizations (high USVs, approximately 55 kHz) during rough-and-tumble play. In an observational study, they further observe that these vocalizations both correlate with and predict appetitive components of the play behavioral repertoire. Additional experiments characterized eliciting conditions for high USVs. Without prior play exposure, rats separated by a screen vocalized less than playing rats, but after only 1 play session, separated rats vocalized more than playing rats. This findings suggested that high USVs were linked to a motivational state rather than specific play behaviors or general activity. Furthermore, individual rats vocalized more in a chamber associated with play than in a habituated control chamber. Finally, congruent and incongruent motivational manipulations modulated vocalization expression. Although play deprivation enhanced high USVs, an arousing but aversive stimulus (bright light) reduced them. Taken together, these findings suggest that high USVs may index an appetitive motivation to play in juvenile rats.     

Latent inhibition in humans: Single-cue conditioning revisited.

Latent inhibition in human Pavlovian conditioning was assessed by way of autonomic responses. In Exp 1 (N?=?72), 3 pairs of conditioning and control groups were preexposed to 0, 10, or 20 to-be-conditioned stimuli (to-be-CSs), respectively. Acquistion of electrodermal 1st-interval and heart rate response conditioning were detectable only in the zero preexposure condition. However, 20 preexposures were needed for latent inhibition of vasomotor response conditioning. In Exp 2 (N?=?48), preexposure to the to-be-CS was compared with preexposure to a stimulus that was not presented during subsequent acquisition. CS preexposure completely abolished electrodermal 1st-interval and heart rate response conditioning. Although vasomotor conditioning was not affected by preexposure, latent inhibition of 2nd-interval electrodermal response conditioning was obtained. Taken together, the data from both experiments provide clear evidence for latent inhibition in human Pavlovian conditioning. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Anticipation of play elicits high-frequency ultrasonic vocalizations in young rats.

The authors provide initial documentation that juvenile rats emit short, high-frequency ultrasonic vocalizations (high USVs, ～55 kHz) during rough-and-tumble play. In an observational study, they further observe that these vocalizations both correlate with and predict appetitive components of the play behavioral repertoire. Additional experiments characterized eliciting conditions for high USVs. Without prior play exposure, rats separated by a screen vocalized less than playing rats, but after only 1 play session, separated rats vocalized more than playing rats. This finding suggested that high USVs were linked to a motivational state rather than specific play behaviors or general activity. Furthermore, individual rats vocalized more in a chamber associated with play than in a habituated control chamber. Finally, congruent and incongruent motivational manipulations modulated vocalization expression. Although play deprivation enhanced high USVs, an arousing but aversive stimulus (bright light) reduced them. Taken together, these findings suggest that high USVs may index an appetitive motivation to play in juvenile rats. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Contextual control over conditioned responding in a latent inhibition paradigm.

We used 1-, 2-, and 3-context designs to study the control exerted by contexts over freezing in rats exposed to a conditioned stimulus (CS) in advance of its pairing with a shock unconditioned stimulus. The latent inhibition observed when preexposure, conditioning, and testing occurred in the same context was attenuated if preexposure occurred in a different context to conditioning and testing. Latent inhibition (i.e., attenuated performance) was restored in a CS-specific manner if preexposure and testing occurred in the same context and conditioning in a different one. Latent inhibition was also reduced by a long retention interval but remained specific for a particular context–CS relation. Finally, CS preexposure resulted in contextual control over the expression of excitatory conditioned performance. The results are discussed in terms of memory, associative, and associative-performance models of CS-preexposure effects. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Decremental effects of context exposure following delay eyeblink conditioning in rabbits.

The conditioning context arises from the relatively static features of the training environment. In rabbit eyeblink conditioning, procedures that retard acquisition (conditioned stimulus [CS] preexposure, unconditioned stimulus preexposure, blocking manipulations) are attenuated by context changes. In this article the authors investigate the effect of context exposure after initial delay conditioning. After conditioned responses (CRs) were established, one group received 6 sessions of context exposure, whereas control groups either remained in their home cages or received exposure to handling and a novel context. Thereafter, all groups received CS-alone testing. The expression of CRs was substantially reduced following context exposure relative to any retention loss in the home-cage control. Exposure to handling and a novel context facilitated the CRs rather than reducing them. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Factors governing single-trial contextual fear conditioning in the weanling rat.

Although contextual fear conditioning emerges later in development than explicit-cue fear conditioning, little is known about the stimulus parameters and biological substrates required at early ages. The authors adapted methods for investigating hippocampus function in adult rodents to identify determinants of contextual fear conditioning in developing rats. Experiment 1 examined the duration of exposure required by weanling rats at postnatal day (PND) 23 to demonstrate contextual fear conditioning. This experiment demonstrated that 30 s of context exposure is sufficient to support conditioning. Furthermore, preexposure enhanced conditioning to an immediate footshock, the context preexposure facilitation effect (CPFE), but had no effect on contextual conditioning to a delayed shock. Experiment 2 demonstrated that N-methyl-D-aspartate (NMDA) receptor inactivation during preexposure impairs contextual learning at PND 23. Thus, the conjuctive representations underlying the CPFE are NMDA-dependent as early as PND23 in the rat. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Excitatory conditioning of individual Drosophila melanogaster..

Demonstrated, in 5 studies, conditioning of the proboscis extension reflex in D. melanogaster. The presentation of paired (conditioning) stimuli produced (a) an increase in the average number of conditioned responses (CRs) over trials, (b) measured differences in performance levels among individual Ss, and (c) greater conditioning among males than females. The presentation of unpaired (control) stimuli produced significantly lower average levels of acquisition responding and a change in the distribution of individual response patterns. Neither central excitatory state nor sensitization induced by the conditioned stimulus/stimuli (CS) or the unconditioned stimulus/stimuli (UCS) directly affected the CR, whereas UCS preexposure adversely affected performance levels. Presenting the unpaired (extinction) stimuli after conditioning produced less of a decline in responding than did an extinction procedure with removal of the UCS. With the ability to identify individual differences in acquisition and extinction patterns, and given the relatively large samples that can be tested simultaneously on the automated stimulation apparatus, it is suggested that it is now possible to make precise behavioral measurements for the behavior-genetic analysis of D. melanogaster with conditioning as the phenotype. (30 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Interaction of tail-pressure stress and d-amphetamine in disruption of the rat's ability to ignore an irrelevant stimulus.

48 male Sprague-Dawley rats received either 0 or 30 preexposures to a tone that was later used as a warning stimulus in a 2-way active avoidance task. Consistent with previous data, tone preexposure resulted in retarded acquisition of the conditioned avoidance response (CAR) in saline-control Ss and in Ss that received chronic administration of dextroamphetamine (DAM; 1 mg/kg, sc). Ss that received tail-pressure stress prior to stimulus preexposure also showed retarded acquisition of the CAR. However, Ss that received a combination of tail pressure and DAM did not show retarded CAR acquisiton following stimulus preexposure. Results suggest an interaction between environmental stressors and DAM in producing attentional deficits. (21 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

CS-US preexposure effects on trace eyeblink conditioning in young rats: Potential implications for functional brain development.

Recent studies of delay eyeblink conditioning (EBC) in young rats have demonstrated different effects of various conditioned and unconditioned stimulus (CS-US) preexposure conditions on learning at different ages. The present study extends this research to trace EBC. Subjects experienced 1 of 3 preexposure conditions (paired CS-US, unpaired CS-US, or no stimuli) at either 20 or 24 days of age. Four days later, they were conditioned using either trace (Experiment 1) or delay (Experiment 2) EBC parameters. Results were similar at both ages tested. Paired preexposure facilitated acquisition of delay but not trace relative to context preexposure. Unpaired preexposure impaired acquisition of both delay and trace. These behavioral findings provide a foundation for hypotheses about the functional maturation of cerebellar, hippocampal, and entorhinal learning circuits. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Drug-induced hypothermia and conditioned place aversion.

Examined the relationship between ethanol's thermal and motivational effects in a place conditioning task. In 3 experiments, male albino rats were exposed to a differential conditioning procedure that paired a distinctive tactile stimulus with ethanol (1.2 or 1.8 g/kg) or lithium chloride (3 meq/kg); a different stimulus was paired with saline. Different groups were exposed to ambient temperatures (Ta) of 5°, 21°, or 32°C during each 60-min conditioning trial. Both ethanol and lithium chloride produced hypothermia and conditioned place aversion in rats conditioned at normal Ta. Exposure to high Ta reduced drug-induced hypothermia, increased activity, and decreased conditioned place aversion. Exposure to low Ta did not enhance drug-induced hypothermia or change conditioned place aversion. In general, these findings support the suggestion that the hedonic effects of ethanol and lithium chloride interact with their thermal effects. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Variations in intensity, interstimulus interval, and interval between preconditioning CS exposures and conditioning with rats.

Investigated the relationship between preconditioning exposure to a stimulus later employed in conditioning as a CS and suppression of a licking response in the presence of that stimulus, in 2 experiments with a total of 216 male albino Sprague-Dawley rats. In Exp. I, a direct relationship was found between intensity of preconditioning stimulus and magnitude of suppression reduction. There was also evidence for the effects of stimulus intensity during conditioning and the operation of generalization decrement when conditioning and test stimulus intensities were not the same. Exp. II showed that preconditioning CS exposure reduced suppression to the test CS on the 1st test trial, regardless of interval between preconditioning exposures or preexposure and conditioning. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

A comparison of contextual and generalized auditory-cue fear conditioning: evidence for similar memory processes

A number of variables influence contextual, but not auditory-cue, fear conditioning. However, several of these variables (isolation, stimulus preexposure, retention interval, and age) affect generalized auditory-cue fear. More generalized fear was found when (a) rats were isolated in a novel environment than when returned to their home cages, (b) the retention interval was 3 hr rather than 24 hr, and (c) in 18-day-old compared with 25-day-old rats. Moreover, preexposure to the auditory cue eliminated the isolation effect. At a behavioral-psychological level, these variables may exert their effects by influencing the processes that construct a memory representation of the stimulus. At a neural systems level, they may influence processing carried out in the thalamo-corticoamygdaloid auditory pathway.     

Effects of amygdala central nucleus lesions on blocking and unblocking.

The effects of lesions of the amygdala central nucleus (CN) on blocking and unblocking of appetitive Pavlovian conditioning were examined in 2 experiments with rats. In both lesioned and unlesioned rats, prior pairing of one CS with a food unconditioned stimulus/stimuli (UCS) blocked the acquisition of conditioning to a 2nd CS when a compound of both stimuli was paired with that same UCS. If the value of the UCS was increased or decreased when the 2nd CS was added, unlesioned rats acquired substantial conditioning to the 2nd cue (unblocking). Unblocking occurred in lesioned rats only when the UCS value was increased. In both lesioned and unlesioned rats, unblocking was prevented if the compound cue was paired with the original UCS prior to the change in UCS value. These data suggest that the CN is involved in increasing attention to signals for significant events but not in tuning out redundant cues. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Renewal and spontaneous recovery, but not latent inhibition, are mediated by gamma-aminobutyric acid in appetitive conditioning.

Previous research has reported a role for the neurotransmitter gamma-aminobutyric acid (GABA) in the extinction and renewal of conditioned fear. Here, the authors examine whether GABA is involved in the acquisition, extinction, renewal, spontaneous recovery, and latent inhibition of appetitive conditioning. Using Long-Evans rats, systemic injection of the GABA A receptor inverse agonist FG 7142 was shown to eliminate ABA renewal (Experiment 1) and spontaneous recovery (Experiment 4) of appetitive responding by selectively reducing the recovery of extinguished magazine approach. Furthermore, treatment with FG 7142 had no effects on acquisition or single-session extinction (Experiment 3) or on the context-specific expression of latent inhibition (Experiment 2). These data suggest that ABA renewal and spontaneous recovery, but not latent inhibition or responding during acquisition and an initial extinction session, are mediated by GABAergic mechanisms in appetitive Pavlovian conditioning. They provide support for the view that renewal and spontaneous recovery share a common psychological mechanism. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Neurotoxic lesions of basolateral, but not central, amygdala interfere with Pavlovian second-order conditioning and reinforcer devaluation effects

Considerable evidence suggests that various discrete nuclei within the amygdala complex are critically involved in the assignment of emotional significance or value to events through associative learning. Much of this evidence comes from aversive conditioning procedures. For example, lesions of either basolateral amygdala (ABL) or the central nucleus (CN) interfere with the acquisition or expression of conditioned fear. The present study examined the effects of selective neurotoxic lesions of either ABL or CN on the acquisition of positive incentive value by a conditioned stimulus (CS) with two appetitive Pavlovian conditioning procedures. In second-order conditioning experiments, rats first received light-food pairings intended to endow the light with reinforcing power. The acquired reinforcing power of the light was then measured by examining its ability to serve as a reinforcer for second-order conditioning of a tone when tone-light pairings were given in the absence of food. Acquisition of second-order conditioning was impaired in rats with ABL lesions but not in rats with CN lesions. In reinforcer devaluation procedures, conditioned responding of rats with ABL lesions was insensitive to postconditioning changes in the value of the reinforcer, whereas rats with CN lesions, like normal rats, were able to spontaneously adjust their CRs to the current value of the reinforcer. The results of both test procedures indicate that ABL, but not CN, is part of a system involved in CSs' acquisition of positive incentive value. Together with evidence that identifies a role for CN in certain changes in attentional processing of CSs in conditioning, these results suggest that separate amygdala subsystems contribute to a variety of processes inherent in associative learning.