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)     

UCS intensity and performance in eyelid conditioning.

Studies of the effects of UCS intensity on performance in human eyelid conditioning are reviewed, particularly with respect to a recent claim that this variable determines the proportion of Ss who condition and not the performance level of individual Ss. The evidence reviewed clearly indicates that UCS intensity does affect the level of performance in Ss who condition. The function involved appears to be negatively accelerated and to approach an asymptote within a relatively small range of intensity values. These effects of UCS intensity are interpreted as reflecting both motivational and associative factors. (28 ref.) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Modulation of the acquisition of the rabbit eyeblink conditioned response by conditioned contextual stimuli.

Three experiments were conducted to ask if conditioned emotional responses (CERs) controlled by contextual cues modulate the acquisition of eyelid conditioned responses (CRs) to discrete conditioned stimuli (CSs). Experiment 1 showed that 30-s auditory stimuli that were paired with aversive shocks to one paraorbital region or the other controlled discriminated CERs, as measured by potentiation of a startle response. In Experiments 2 and 3, similarly trained 30-s stimuli served as contexts in which 1,050-ms CSs were paired with a paraorbital unconditioned stimulus (US). Reinforced contexts both impaired (Experiments 2A and 2B) and facilitated (Experiment 3B) acquisition of the eyeblink CR, depending on the locus of the USs involved. The data are consistent with the interpretation that CERs controlled by contextual cues facilitate CR acquisition, but do so in the face of blocking effects of CR tendencies also conditioned to the contextual cues. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Associative and nonassociative theories of the UCS preexposure phenomenon: Implications for Pavlovian conditioning.

Excitatory Pavlovian conditioning of a discrete CS is attenuated by prior exposure to the UCS. The UCS preexposure phenomenon is observed in a variety of Pavlovian conditioning procedures as diverse as eyelid conditioning, the conditioned emotional response, and conditioned taste aversion learning. This article discusses the variables that affect the UCS preexposure phenomenon and uses this information in evaluating both associative and nonassociative accounts of the phenomenon. At least one associative account, based on context blocking, and at least one nonassociative account, based on central habituation of the emotional response to the UCS, remain viable. (71 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Changes in pain reactivity induced by unconditioned and conditioned excitatory and inhibitory stimuli.

Investigated the effects of aversive-conditioning components on the reactivity of rats to pain. After training in Exp 1 with a discrete conditioned stimulus (CS) for a shock unconditioned stimulus (US), different groups were exposed to the CS, US, CS/US compound, just the training context, or none of those immediately prior to a hot-plate test assessing the latency of a paw-lick response. Relative to no exposure and context alone, the CS produced a shorter latency (sensitization effect), whereas the US produced a longer latency (hypoalgesic effect) that was actually augmented by the CS/US compound. Whereas the US-induced hypoalgesia was unaffected by naloxone, hypoalgesia produced by the CS/US compound was appreciably decremented by the drug. Exp 2 showed the same effects with parameters more typical of conditioning research. Exp 3 compared signals for the presence (CS+) and absence (CS–) of the US. The CS– did not itself affect pain reactivity, but it inhibited the effects of the CS+, US, and CS+/US compound. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

UCS intensity and instructional set in classical eyelid conditioning: Discrimination conditioning and signal-detection analysis.

Conducted discrimination eyelid conditioning at 2 UCS intensities under inhibitory, neutral, and facilitatory instructional sets, in a experiment involving 144 undergraduates in 6 groups. Instructional set yielded receiver operating characteristic curves that were reasonably straight lines on a normal deviate plot. The tentative conclusion from signal-detection theory of an equal discriminability function across instructional sets was contrasted with 4 indices of discrimination, indicating significant but mutually contradictory changes in discrimination as a function of instructional set. Discrimination differences were produced by UCS intensity, particularly under the neutral instructions. (French summary) (16 ref.) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

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)     

Extending conditioned stimuli before versus after unconditioned stimuli: Implications for real-time models of conditioning.

In four experiments using the conditioned suppression procedure with rats, we compared the effects of extending conditioned stimuli (CSs) before versus after reinforcement (called B vs. A extensions). In Experiments 1 and 2, Group 0 (no extension) received 2-min noise CS trials (3 per day in Experiment 1, 1 per day in Experiment 2) that terminated with a 1-s grid shock unconditioned stimulus (US). For Group B, the CS began 12 min before the US; for Group A, the CS began 2 min before the US but persisted for 10 min past US termination. In Experiments 3 and 4, similar trials (3 per day in Experiment 3, 1 per day in Experiment 4) included a 2-min light CS that always terminated with the US; thus the noise CS became a systematically manipulated context cue in which light-shock pairings were embedded. In Experiments 1 and 2 we found asymmetrical effects of CS extensions: B extensions weakened conditioning more than did A extensions. In Experiments 3 and 4 we found symmetrical effects: A and B extensions weakened context conditioning equally. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Stress enhances excitatory trace eyeblink conditioning and opposes acquisition of inhibitory conditioning

Exposure to a brief, stressful event is reported to facilitate classical eyeblink conditioning in the male rat (Rattus norvegicus) by use of a delay paradigm in which the conditioned stimulus (CS) and unconditioned stimulus (US) overlap and coterminate. This study examined the effects of stress on trace conditioning, a task in which the CS and US were separated by 500 ms. Experiment 1 showed that exposure to brief (1 s), low-intensity (1 mA) tailshocks facilitated acquisition 24 hr later. Experiment 2 showed that stressor exposure did not affect retention or extinction of trace conditioning in rats that were stressed after acquisition. Experiment 3 showed that exposure to the same stressor opposed acquisition of inhibitory conditioning. These results suggest that exposure to a stressful event persistently facilitates acquisition of trace conditioning and enhances a bias toward acquiring positive versus negative associations.     

Discriminated lateralized eyeblink conditioning in the rabbit: An experimental context for separating specific and general associative influences.

Four experiments demonstrated discriminated lateralized eyeblink conditioning in 38 male rabbits and showed how the phenomenon may be used to differentiate between the reflexive and emotive consequences of Pavlovian conditioning. Exps 1, 2, and 3 characterized how 2 conditioned stimuli (CSs), contemporaneously trained with left vs right paraorbital unconditioned stimuli (UCSs), can produce different CRs, each involving predominant closure of the eye ipsilateral to its UCS. Exp 4 showed how the associative tendencies controlled by additional stimuli could be evaluated by presentations in compound with such discriminanda: A 30-sec stimulus, presumed to acquire a conditioned emotional response but no eyeblink CR, equally potentiated the eyelid CRs elicited by both CSs. A 1,050-msec CS that evoked an eyeblink CR in isolation also increased the responding to both CSs but biased it toward its own lateralized CR. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Effects of amygdala lesions on reflex facilitation and conditioned response acquisition during nictitating membrane response conditioning in rabbit.

Demonstrated that large lesions of the amygdala disrupt the maintenance of reflex facilitation of the unconditioned nictitating membrane (NM) response and slow the acquisition of conditioned NM responses in rabbits. Before behavioral training, the central nucleus of the amygdala and adjacent areas were lesioned electrolytically. In Exp 1, the lesioned animals exhibited no reflex facilitation of the unconditioned NM response at conditioned stimulus (CS)–unconditioned stimulus (UCS) intervals of 125–8,000 ms. In Exps 2 and 3, in which 1 CS–UCS interval (500 ms) was used, the lesions disrupted the maintenance of reflex facilitation but did not alter the facilitation exhibited in the 1st block of training. The lesions retarded the acquisition of conditioned NM responses when the 1,000-Hz tone CS intensity was 65 dB, but not when the intensity was 85 dB. (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)     

Evaluative conditioning in the picture–picture paradigm with random assignment of conditioned stimuli to unconditioned stimuli.

Human participants were allocated to 1 of 3 groups. In the conditioning group, each conditioned stimulus (CS)–unconditioned stimulus (UCS) pair was presented 7 times during the acquisition phase. Participants who were assigned to the extinction group saw 5 additional presentations of each CS in isolation after the 7 presentations of each CS–UCS pair. In the latent inhibition group, the CS-only trials were presented before the CS–UCS trials. Overall, a significant evaluative conditioning effect was observed. This effect cannot be dismissed on the basis of the arguments developed by A. P. Field and G. C. L. Davey (see records 1997-42912-009, 1998-11983-008, and 1999-10526-006), and the results thus provide strong evidence for the associative nature of evaluative conditioning. The results are also in line with other findings, which showed that evaluative conditioning is resistant to extinction. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Functional inactivation of the lateral and basal nuclei of the amygdala by muscimol infusion prevents fear conditioning to an explicit conditioned stimulus and to contextual stimuli.

The GABAa agonist, muscimol (0.5 μg in 0.5 μl saline), or vehicle was infused into the lateral and basal amygdala nuclei prior to fear conditioning or testing in rats. Rats given muscimol before conditioning and saline before testing showed much less freezing to the conditioned stimulus (CS) and the context than did controls given saline before training and testing. Rats given saline before training and muscimol prior to testing also showed low levels of freezing to the CS and the context. In follow-up procedures, rats with acquisition initially blocked by pretraining muscimol infusions froze in a manner similar to that of controls when retrained and retested with saline infusions. Rats trained with saline but tested with muscimol presumably became conditioned but could express the learning. When retested with saline, they froze in the same manner as controls. Thus, activity in the lateral and basal amygdala appears to play an essential role in the acquisition and expression of fear conditioning. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Temporal specificity of fear conditioning: Effects of different conditioned stimulus--unconditioned stimulus intervals on the fear-potentiated startle effect.

Separate groups of rats were given 30 pairings of a light (conditioned stimulus, CS) and a 500-ms shock (unconditioned stimulus, US) at CS–US intervals of 0, 25, 50, 100, 200, 800, 3,200, 12,800, or 51,200 ms. Other groups had lights and shocks inconsistently paired. The startle reflex was elicited 2–4 days later with a noise burst alone or 25–51,200 ms after light onset. After CS–US pairings over a range of intervals (25–51,200 ms), startle was potentiated in testing, as rapidly as 50 ms after light onset. Magnitude of potentiation and resistance to extinction were generally greater with longer CS–US intervals. In several groups, potentiation was maximal at a test interval that matched the CS–US interval used in training. This temporal specificity sharpened with increasing numbers of training trials but even occurred with a single training trial in which a 51,200-ms CS–US interval was used. Data indicate that even during simple fear conditioning (FC), animals rapidly learn a temporal CS–US relationship. This has implications for understanding the neural mechanisms of FC. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Effects of bed nucleus of the stria terminalis lesions on conditioned anxiety: Aversive conditioning with long-duration conditional stimuli and reinstatement of extinguished fear.

Four experiments investigated the effects of lesions of the bed nucleus of the stria terminalis (BNST) on conditioned fear and anxiety. Though BNST lesions did not disrupt fear conditioning with a short-duration conditional stimulus (CS; Experiments 1 and 3), the lesion attenuated conditioning with a longer duration CS (Experiments 1 and 2). Experiment 3 found that lesions attenuated reinstatement of extinguished fear, which relies on contextual conditioning. Experiment 4 confirmed that the lesion reduced unconditioned anxiety in an elevated zero maze. The authors suggest that long-duration CSs, whether explicit cues or contexts, evoke anxiety conditioned responses, which are dissociable from fear responses to shorter CSs. Results are consistent with behavioral and anatomical distinctions between fear and anxiety and with a behavior-systems view of defensive conditioning. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Effects of bilateral eye movements on the retrieval of item, associative, and contextual information.

Two experiments are reported that investigate the effects of saccadic bilateral eye movements on the retrieval of item, associative, and contextual information. Experiment 1 compared the effects of bilateral versus vertical versus no eye movements on tests of item recognition, followed by remember-know responses and associative recognition. Supporting previous research, bilateral eye movements enhanced item recognition by increasing the hit rate and decreasing the false alarm rate. Analysis of remember-know responses indicated that eye movement effects were accompanied by increases in remember responses. The test of associative recognition found that bilateral eye movements increased correct responses to intact pairs and decreased false alarms to rearranged pairs. Experiment 2 assessed the effects of eye movements on the recall of intrinsic (color) and extrinsic (spatial location) context. Bilateral eye movements increased correct recall for both types of context. The results are discussed within the framework of dual-process models of memory and the possible neural underpinnings of these effects are considered. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Backward inhibitory conditioning with signaled and unsignaled unconditioned stimuli: Distribution of trials across days and intertrial interval.

Through summation tests in conditioned suppression with rats we assessed the effects of distribution of trials across days (Experiment 1) and intertrial interval (ITI) (Experiment 2) on the degree of backward conditioned inhibition established through signaled and unsignaled unconditioned stimuli (USs). Two backward conditioned inhibitory stimuli (CS-s) were established within subjects: One backward CS- followed signaled shocks; the other followed unsignaled shocks. After 12 daily sessions (Experiment 1), the signaled backward CS- was strongly inhibitory and significantly more inhibitory than the unsignaled backward CS-. When the same number of trials occurred in a single long session, performances to both CS-s converged at moderate levels. At the 90-s ITI, (Experiment 2) the signaled and unsignaled backward CS-s were nearly equivalent in effectiveness. When the ITI was 540 s, performances diverged, and signaled backward CS- was substantially more effective; the longer ITI facilitated inhibitory backward conditioning based upon signaled USs but prevented the development of inhibitory backward conditioning based upon unsignaled USs. These functionally opposite effects on backward conditioned inhibition, depending on whether the US was signaled or not, are anticipated by Wagner's "standard operating procedure" (SOP) model of short-term memory. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Comparator mechanisms and conditioned inhibition: Conditioned stimulus preexposure disrupts Pavlovian conditioned inhibition but not explicitly unpaired inhibition.

Three conditioned lick-suppression experiments with rats examined the effects of pretraining exposure to the conditioned stimulus (CS) on behavior indicative of conditioned inhibition. After CS-preexposure treatment, subjects received either Pavlovian conditioned inhibition training or explicitly impaired inhibition training with the preexposed CS. The inhibitory status of the CS was then assessed with a retardation (Experiment 1) or a summation (Experiment 2) test. Experiment 3 controlled for the unconditioned stimulus-preexposure effect being a potential confound in Experiments 1 and 2. As predicted by the comparator hypothesis (R. R. Miller & L. D. Matzel, 1988), the CS–context association that developed during the CS-preexposure phase disrupted the expression of Pavlovian conditioned inhibition but not the expression of explicitly impaired inhibition. (PsycINFO Database Record (c) 2010 APA, all rights reserved)