Associative effects of US preexposure: Modulation of conditioned responding by an excitatory training context.

Conducted 2 experiments with 120 naive Sprague-Dawley rats to examine factors that contribute to retarded emergence of conditioned responding to a conditioned stimulus/stimuli (CS) trained in a context in which unsignaled unconditioned stimulus/stimuli (UCS) had previously been administered. In both experiments, water-deprived Ss were used in a conditioned lick suppression task to measure the conditioned response (CR) elicitation potential of the CS and the training context. From Exp I, it was determined that nonreinforced exposure to the excitatory context after UCS preexposure and prior to CS–UCS pairings in that context eliminated the CR deficit observed on a subsequent test of the CS. From Exp II, it was determined that the recovery induced by contextual deflation after CS training was specific to deflation of the context in which the CS was trained as opposed to another excitatory context. (28 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Mechanisms underlying retarded emergence of conditioned responding following inhibitory training: Evidence for the comparator hypothesis.

The comparator hypothesis posits that conditioned responding is determined by a comparison at the time of testing between the associative strengths of the conditioned stimulus/stimuli (CS) and stimuli proximal to the CS at the time of conditioning. The hypothesis treats all associations as being excitatory and treats conditioned inhibition as the behavioral consequence of a CS that is less excitatory than its comparator stimuli. Conditioned lick suppression by rats was used to differentiate 4 possible sources of retarded responding to an inhibitory CS. These include habituation to the unconditioned stimulus/stimuli (UCS), latent inhibition to the CS, blocking of the CS-UCS association by the conditioning context, and enhanced excitatory associations to the comparator stimuli. Prior research has demonstrated the 1st 3 phenomena. Therefore, we employed parameters expected to highlight the 4th one—the comparator process. In Exp I, our negative contingency training produced a conditioned inhibitor that passed inhibitory summation and retardation tests. In Exp II we found transfer of retardation from an inhibitory CS to a novel stimulus when the location where retardation-test training occurred was excitatory. In Exp III, extinction of the conditioning context attenuated retardation regardless of whether extinction occurred before or after the CS-UCS pairings of the retardation test. Exp IV demonstrated that habituation to the UCS did not contribute to retardation in the present case. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Memory for the conditioned response: The proactive effect of preexposure to potential conditioning stimuli and context change.

Three experiments with 48 cats investigated memory for CR as a function of proactive inhibition. The proactive operation was the preexposure to quasi-random presentations of the potential CS and UCS. The possible CSs were light and tone, and the UCSs were brief mild shocks to either the right or left paw, which produced a brisk leg jerk. In Exp I, all possible combinations of CS and UCS components of the eventual CR were present in the preexposure period for one or another group as in the traditional interference paradigms of human paired-associate memory research. Exp II demonstrated that the decline cannot be attributed to a strategy type of interpretation that asserts that when the retention–extinction situation occurs, Ss "backward scan" and judge themselves to be once again in the preexposure period. Performance immediately after reaching the conditioning criterion did not differ between the controls that experienced no preexposure and the experimentals, but it did so after the 10-wk retention interval. Exp III investigated the role of context in the memory deficits by maintaining the same context in the preexposure, conditioning, and memory test situations or giving the preexposure experience in an environment different from the other 2 situations. Context change greatly reduced but did not eliminate the proactive inhibition. It is concluded that the CR is readily forgotten given appropriate interference and does not differ from other kinds of learning in this respect. (27 ref) (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)     

Latent inhibition and stimulus generalization of the classically conditioned nictitating membrane response in rabbits (Oryctolagus cuniculus) following hippocampal ablation.

30 male and female New Zealand albino rabbits received 0 to 450 exposures of a tone CS prior to classical defensive conditioning of the nictitating membrane response based on an infraorbital eye shock UCS. Tone preexposure resulted in retarded conditioning in normal Ss, but was not present in Ss with bilateral dorsal hippocampectomy produced by aspiration. Controls with bilateral neocortical and callosal aspiration lesions demonstrated a latent inhibition effect similar to that shown by normal nonoperated Ss. The failure of CS preexposure to retard conditioning in hippocampal Ss was not due to differences in threshold of the conditioned response to the CS or to differences in response mechanisms as determined by tests of habituation and dishabituation of the UCR. A subsequent experiment with 24 Ss used combined-cue summation tests to confirm the fact that preexposure did not endow the tone with conditioned as well as latent inhibitory properties. Finally, tests of stimulus generalization along the auditory frequency dimension indicated flatter relative gradients for hippocampals than for nonoperated controls, with cortical controls in between. (40 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Role of the hippocampus in blocking and conditioned inhibition of the rabbit's nictitating membrane response.

In Exp I, bilateral aspiration of the dorsal hippocampus produced a disruption of blocking of 30 New Zealand rabbits' nictitating membrane response in L. J. Kamin's (1968, 1969) 2-stage paradigm, but had no effect on the formation of a Pavlovian conditioned inhibitor in Exp II (27 Ss). Results of Exp I indicate that normal Ss and those with cortical lesions given conditioning to a light-plus-tone CS gave CRs to both light and tone during nonreinforced presentations of each (test phase). If, however, compound conditioning was preceded by tone acquisition, only the tone elicited a CR during testing; that is, blocking was observed. In Ss with hippocampal lesions, however, CRs were given to both light and tone during testing whether or not compound conditioning was preceded by tone acquisition. Data from Exp II show that Ss with hippocampal lesions could discriminate as well as normal Ss and those with cortical lesions between a light (CS+) and light plus tone (CS-). In addition, when the inhibitory tone was subsequently paired with the UCS in retardation testing, Ss in all 3 lesion conditions acquired the CR at the same rate. Thus, it appears that hippocampal lesions do not disrupt conditioned inhibition. Results are taken as support for the view that the hippocampus is responsible for "tuning out" stimuli that have no adaptive value to the organism. (27 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Malleability of conditioned associations: Path dependence.

Using conditioned suppression of barpressing to investigate the stability of a conditioned stimulus–unconditioned stimulus (CS–UCS) association, the present authors gave 151 water-deprived rats either a few pairings of the CS with a strong footshock UCS or many pairings with a weak footshock UCS so that barpress suppression in response to CS was equated. Exp I established training parameters that yielded this equivalence. Specifically, rapid acquisition to a preasymptotic level of responding with strong shock produced suppression comparable to the asymptotic level reached more slowly with weak shock. Exp II showed that although equivalent performance was obtained from extensive conditioning with a weak shock or limited conditioning with a strong shock, only extensive conditioning with weak shock resulted in retarded acquisition of an association between that same CS and a footshock level perceived as midway between the 2 initial training shock intensities as implied by asymptotic performance in Exp I. Exp III demonstrated that the observed retardation in Ss given many conditioning trials with weak shock was CS-specific. It is concluded that the malleability of learned behavior is not simply a function of initial associative strength but is dependent on the path during initial acquisition. (18 ref) (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)     

Human blink startle during aversive and nonaversive Pavlovian conditioning.

Potentiation of blink startle during aversive and nonaversive Pavlovian single-cue conditioning was assessed in human Ss. In Exp 1 (N?=?89), the conditioning group received paired presentations of a visual CS and an unconditioned stimulus/stimuli (UCS), whereas the control group was presented with a random sequence. The UCS was an electric shock for half the Ss and a nonaversive reaction time (RT) task for the other half. Electrodermal conditioning was evident regardless of the nature of the UCS, but blink potentiation was found only in the conditioning group that had been trained with the aversive UCS. These results were replicated in Exp 2 (N?=?65), in which a nonaversive UCS of increased motivational significance was used. Thus, only aversive conditioning seems to affect the affective valence of the CS, at least as reflected by changes in a skeletal reflex. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Unconditioned stress-induced analgesia following exposure to brief footshock.

Four experiments, with 136 male Sprague-Dawley rats, examined the properties of unconditioned analgesia elicited by electric footshock stimuli using UCS parameters typical of aversive conditioning paradigms. In all experiments, analgesia was inferred from the latency to paw lick in response to painful thermal stimulation in the hot-plate assay. In Exp I, Ss exposed to a 1-sec, 2-mA shock UCS showed significantly longer latencies to respond to painful thermal stimulation than nonshocked controls, whereas nonsignificant increases in response latencies were observed with 1-sec shock UCS of either 0.5 or 1.25 mA. In Exp II, Ss exposed to a 2-mA electric shock UCS showed systematic increases in latencies to respond to painful thermal stimulation as the duration of the shock was varied between 0.5 and 2 sec. Exp III showed that this form of shock-induced analgesia was of short temporal duration. Specifically, significant increases in latencies to respond to painful thermal stimulation occurred 30 but not 90 or 300 sec following exposure to shock. Exp IV demonstrated that this form of analgesia was unaffected by pretreatment with the opiate receptor antagonist naloxone HCl in ip dosages of 1, 5, 10, or 20 mg/kg. Finally, there was no evidence showing that environmental stimuli paired with shock presentations acquired the capacity to evoke analgesia as a conditioned response. Implications of shock-induced analgesia for the study of aversive conditioning and behavior are discussed. (26 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

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)     

Pavlovian aversive context conditioning using carbon dioxide as the unconditional stimulus.

Four experiments were conducted to examine the utility of carbon dioxide (CO?) as an aversive unconditioned stimulus/stimuli (UCS) in a Pavlovian context conditioning paradigm. Exp 1 demonstrated that rats exposed to CO? in a distinctive context showed elevated levels of freezing relative to controls. Exp 2 replicated this basic effect with a modified conditioning procedure and additionally demonstrated conditioned analgesia. Exp 3 demonstrated a positive monotonic relationship between UCS duration and resistance to extinction of freezing behavior as well as conditioned analgesia. Exp 4 demonstrated extinction and an extinction-related phenomenon, renewal. These studies clearly demonstrate the utility of CO? as a Pavlovian UCS. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Pavlovian second-order conditioned analgesia.

Three experiments, with 118 Sprague-Dawley rats, assessed conditioned analgesia in a Pavlovian 2nd-order conditioning procedure by using inhibition of responding to thermal stimulation as an index of pain sensitivity. In Exp I, Ss receiving 2nd-order conditioning showed longer response latencies during a test of pain sensitivity in the presence of the 2nd-order conditioned stimulus (CS) than Ss receiving appropriate control procedures. Exp II found that extinction of the 1st-order CS had no effect on established 2nd-order conditioned analgesia. Exp III evaluated the effects of post 2nd-order conditioning pairings of subcutaneous morphine sulfate (10–20 mg/kg) and the shock unconditioned stimulus/stimuli (UCS). Ss receiving paired morphine–shock presentations showed significantly shorter response latencies during a hot-plate test of pain sensitivity in the presence of the 2nd-order CS than did Ss receiving various control procedures; 2nd-order analgesia was attenuated. Data extend the associative account of conditioned analgesia to 2nd-order conditioning situations and are discussed in terms of the mediation of both 1st- and 2nd-order analgesia by an association between the CS and a representation or expectancy of the UCS, which may directly activate endogenous pain inhibition systems. (52 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Sexual approach conditioning: Tests of unconditioned stimulus devaluation using hormone manipulations.

Contents of learning that result from CS–unconditioned stimulus/stimuli (UCS) pairings in sexual approach conditioning were explored with male Japanese quail (Coturnix coturnix japonica). Sexual motivation of Ss conditioned to approach an arbitrary stimulus in a Pavlovian sexual conditioning paradigm was reduced by exposing them to a short photoperiod. Decreased sexual motivation resulted in a decline in sexually conditioned approach behavior (Exps 1 and 2). Responding was restored when Ss were returned to a long photoperiod (Exp 1) and when exogenous testosterone was administered (Exp 2). Decreased sexual motivation did not affect food-conditioned approach behavior (Exp 3). These results suggest that sexually conditioned approach behavior is mediated by a representation of the UCS, which is activated by the CS. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

NMDA processes mediate anterograde amnesia of contextual fear conditioning induced by hippocampal damage: Immunization against amnesia by context preexposure.

Hippocampal lesions in rats produce both a retrograde and an anterograde amnesia of contextual fear conditioning. The present experiments examined the anterograde deficit in context conditioning involving a total of 113 rats in 4 experiments. The deficit produced by electrolytic hippocampal lesions was apparent when training occurred on 7, 14, or 28 days following surgery, confirming the durability of the amnesia. The role of the hippocampus in context conditioning may be related to an N-methyl-D-aspartate (NMDA) receptor-mediated process. Both NMDA hippocampal lesions and intrahippocampal administration of an NMDA antagonist produced anterograde amnesia. Ss preexposed to the conditioning context 28 days prior to hippocampal lesioning were protected from the deficit normally produced by the lesions. Thus, the hippocampus must form a contextual representation during preexposure that is subsequently stored elsewhere. Once formed this representation of the context can be associated with an unconditioned stimulus/stimuli (UCS). (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Associative regulation of Pavlovian fear conditioning: Unconditioned stimulus intensity, incentive shifts, and latent inhibition.

Conditional stimuli (CS) associated with painful unconditional stimuli (UCS) produce a naloxone-reversible analgesia. The analgesia serves as a negative-feedback regulation of fear conditioning that can account for the impact of UCS intensity and CS predictiveness on Pavlovian fear conditioning. In Exp 1, training under naloxone produced learning curves that approached the same high asymptote despite UCS intensity. Shifting drug treatment during acquisition had effects that paralleled UCS intensity shifts. In Exp 3, naloxone reversed Hall-Pearce (1979) negative transfer using a contextual CS, indicating that conditional analgesia acquired during the CS–weak-footshock phase retards acquisition in the CS–strong-footshock phase. Exp 5 used a tone CS in both a latent-inhibition and a negative-transfer procedure. Only negative transfer was blocked by naloxone. Therefore, negative transfer but not latent inhibition is mediated by a reduction of UCS processing. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The septohippocampal cholinergic system and classical conditioning of the rabbit's nictitating membrane response.

28 New Zealand albino rabbits received bilateral microinjections of scopolamine (1 μl) or saline into either the dorsal hippocampus (Exp I) or the medial septal nucleus (Exp II). Ss then underwent classical conditioning of the nictitating membrane response in which a light served as a CS and eye shock served as the UCS. Results indicate that whereas hippocampal injections of scopolamine had no effect on conditioning, scopolamine injected into the medial septum retarded acquisition of the response. A 3rd experiment indicated that this retardation of conditioning was not due to changes in sensitivity to either the CS or UCS. Results are discussed in terms of accumulating evidence that manipulations that produce certain patterns of activity in the hippocampus are detrimental to acquisition of the nictitating CR. (43 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Differential control by context in the inflation and reinstatement paradigms.

Examined, in 5 conditioned suppression experiments, the influence of summation between fear of the CS and the context in experimental paradigms in which the rat is exposed to UCSs following conditioning or extinction. Context-preference tests assessed contextual fear. In Exps I–III with 88 female Wistar rats, the inflation paradigm, in which fear of a CS paired with a weak UCS is enhanced by exposure to intense UCS alone, was investigated. Results show that the contextual fear that was present when the target CS was tested was reduced by presenting the intense UCSs in a different context, by exposing Ss to the context following their presentation, and by signaling the intense UCSs with a 2nd CS. In Exp IV with 32 female Wistar rats, UCS exposures following conditioning or extinction both produced contextual fear, but only fear of the extinguished CS was reinstated by that fear. In Exp V with 32 female Wistar rats, identical amounts of contextual fear reinstated fear of an extinguished CS, but not a nonextinguished CS, when the 2 types of CSs were arranged to evoke comparable amounts of fear prior to testing. It is suggested that contextual fear plays a role in the reinstatement paradigm but not in the inflation paradigm. (33 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Acquisition of conditioned associations in Hermissenda: Additive effects of contiguity and the forward interstimulus interval.

Examined conditioned suppression of photokinesis (CSPK) by the marine mollusc in 3 experiments. In each experiment, groups of Ss received light (conditioned stimulus, CS) paired with high-speed orbital rotation (unconditioned stimulus, UCS), light and rotation explicitly unpaired, or no exposure to these stimuli. 24 hrs after training, all Ss were tested for CSPK in the presence of the light. 50 CS–UCS pairings resulted in a marginal CSPK, whereas 100 and 150 pairings produced strong CSPK. In Exp 2, delay between CS onset and UCS onset was varied between 1 and 10 s. The 10-s interstimulus interval (ISI) did not support conditioning, whereas 1-s and 2-s ISIs were effective. In Exp 3, CS–UCS pairings in which the CS preceded the onset of the UCS and ended with the offset of the UCS evoked stronger CSPK than either a CS that preceded the UCS and ended with its onset or a CS that was paired in simultaneous compound with the UCS. CS–UCS contiguity and the forward ISI act additively to establish the CS–UCS association. No differences were observed between groups that were untreated and that received the CS and UCS unpaired. Similarities are noted in the temporal characteristics of associative learning in these Ss and vertebrate species. (PsycINFO Database Record (c) 2010 APA, all rights reserved)