Effects of discrimination training on responding during a compound conditioned stimulus.

Four experiments examined responding in the presence of a triple-element compound ABC after discrimination training in which 2 compounds, AB and BC, signaled the delivery of food and 1 element alone, B, signaled the absence of food. In Exps 1 and 2, using rats, responding during ABC was more vigorous than in a control group for which A and C but not B had been individually paired with food. This finding was replicated in Exp 3, which used pigeons, and in Exp 4, where all 3 stimuli of the control condition were individually paired with food. The results are more consistent with a configural than with an elemental theory of learning. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Intertrial interval effects in classically conditioned fear to a discrete conditioned stimulus and to situational cues.

In Exp I fear was classically conditioned in a total of 240 female hooded and Sprague-Dawley rats with a discrete conditioned stimulus (CS) at intertrial intervals (ITIs) of 15, 45, 75, 105, 165, or 225 sec and in Exp II, with an additional 144 Ss, with or without a discrete CS at ITIs of 165, 225, or 285 sec. The amount of fear conditioned to situational cues and to the discrete CS plus situational cues was then measured by the learning of a hurdle-jumping response which allowed escape from the fear-eliciting stimuli. Results suggest that as ITI was lengthened fear conditioned to situational cues alone and to the discrete CS increased. However, following conditioning with a discrete CS, fear elicited by situational cues increased with ITI but then decreased, presumably because a discrimination had been formed between the situational cues and the compound of CS plus situational cues. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

When pentobarbital is the conditioned stimulus and amphetamine is the unconditioned stimulus, conditioning depends on the type of conditioned response.

Injections of drugs into rats were used as conditioned stimuli (CSs) and as unconditioned stimuli (UCSs). With heart rate (HR) conditioning, the pentobarbital CS produces a higher HR than under control conditions. With avfail (aversion failure) conditioning, the pentobarbital CS loses much of its capacity to induce a conditioned taste aversion. HR conditioning was obtained with forward delays of up to 30 min and backward delays of up to 270 min, where the delays are defined by the interinjection interval. Avfail was obtained with forward delays of up to 270 min but not with backward delays. Neither HR conditioning nor avfail were context specific but could be demonstrated in a test apparatus after pairings that occurred in the home cage. This indicated that the external environment was not an important part of the effective stimulus complex. When HR conditioning was obtained, its latency and duration was not related to the delay between the CS and UCS injections or whether they were forward or backward. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Selective attention to elements of a morphine stimulus: Idiosyncratic stimulus additivity of incidental cues.

Twelve male Sprague-Dawley rats (Rattus norvegicus) were trained to discriminate between the presence and absence of 5.6 mg/kg morphine sulfate in a lever-press operant task under a fixed-ratio 10 schedule of food delivery. Stimulus cross-generalization profiles were determined for a number of over-the counter (OTC) medications that were hypothesized to engender elements of a compound morphine cue including sedation and lethargy: dextromethorphan, doxylamine, diphenhydramine, pyrilamine, loperamide, and the B vitamins, pyridoxine, thiamine, and cyanocobalamin. On the basis of the individual rat's cross-generalization profile, each rat was retested for stimulus element additivity following the administration of various OTC binary and ternary combinations. For each rat, a test combination was formulated that engendered > 90% morphine-appropriate responding. These test combinations were idiosyncratic, exhibited high test-retest reliability, and followed rules predicted by simple effect additivity. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Conditioning across the duration of a backward conditioned stimulus.

Five conditioned suppression experiments examined the extent to which an appetitively motivated lever-press response can be punished by different components of a backward conditioned stimulus (CS). Using a 0-s unconditioned stimulus UCS–CS interval, Experiments 1 and 2 showed that the initial 3 s of a normally 30-s backward CS served as a more effective punisher than the CS as a whole, Experiment 3 found no such effect if the UCS–CS interval were 3 s rather than 0 s. Experiments 4A and 4B found that if the UCS–CS interval were 0 s, the initial part of the backward CS acquired excitatory properties although the CS as a whole passed a summation test for conditioned inhibition. By contrast, the 3-s UCS–CS interval supported inhibitory conditioning across the whole duration of the backward CS. Taken together, these findings support a modified version of Wagner's sometimes opponent process model, which suggests that different components of a backward CS become either excitatory or inhibitory depending on the components' temporal proximity to the UCS. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Pro-Leu-Gly-NH? serves as a conditioned stimulus in the acquisition of conditioned tolerance.

The effect of Pro-Leu-Gly-NH? (MIF) on the acquisition of tolerance to morphine-induced antinociception and its efficacy as a cue predictive of morphine administration was examined. Daily administration of MIF prior to morphine injection did not attenuate the acquisition of tolerance to the antinociceptive properties of morphine, as measured by the latency to hindpaw lick in a hot-plate test of analgesia. When the animals were tested 72 hrs later without MIF pretreatment, they appeared to lose tolerance, as indicated by longer latencies to paw lick. These data suggest that in some situations MIF may interfere with the acquisition of tolerance by acting as a cue that reliably predicts the antinociceptive properties of morphine. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Odor-guided fear conditioning in rats: 2. Lesions of the anterior perirhinal cortex disrupt fear conditioned to the explicit conditioned stimulus but not to the training context.

Previous studies examining the neural substrates of fear conditioning have indicated unequivocally that the acquisition and expression of conditioned fear depends critically on the integrity of the amygdala. The extent to which the rhinal cortical areas contribute to fear conditioned to either the explicit conditioned stimulus (CS) or to the training context is less clear, however. The effects of pretraining lesions of the anterior perirhinal (PRH) cortex on fear conditioned to an explicit odor CS and to the context in which CS–unconditioned stimulus pairing took place was examined in rats. Rats with PRH cortex lesions demonstrated a robust attenuation of fear conditioned to the explicit CS, but no attenuation of fear conditioned to the training context. These data suggest that the PRH cortex is an important component of the neural system supporting the association between olfactory cues and footshock and add to a growing body of evidence implicating the rhinal cortical regions in associative learning. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Conditioned stimulus control in the rat circadian system depends on clock resetting during conditioning.

The authors examined the ability of a conditioned stimulus (CS; mild air disturbance) previously paired with an entraining light pulse to reset the circadian pacemaker in rats. Rats were entrained to a single 30-min light stimulus delivered every 25 hr or 24 hr (T cycle). Each daily light presentation was paired with the CS. After at least 20 days of stable entrainment to each of the T cycles, the rats were allowed to free run and were then presented with the CS at circadian time 15. CS-induced phase shifts in wheel-running activity rhythms were taken as evidence for conditioning. For the most part, conditioning occurred after CS-light pairings on the 25-hr but not 24-hr T cycle. The results suggest that CS control of the circadian clock phase depends on the effect that the entraining light pulse has on the clock during conditioning. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Influence of similarity of components of a serial conditioned stimulus on conditioned fear in rats.

Reports 2 experiments in which 80 male and 96 female Blue Spruce rats were presented a serial CS procedure consisting of 2 components: S1 followed by S2 (S1/S2). In both experiments the stimulus similarity of S1 to S2 in terms of tonal frequency was systematically manipulated. Exp I tested the effects of similarity of components in a standard shuttle-box avoidance situation. Exp II employed a conditioned emotional response paradigm measuring the suppression of consummatory licking. Results suggest that the amount of fear elicited by S1 is a direct function of the stimulus similarity of S1 to S2, and support a generalization interpretation of fear transference. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Some factors that determine the influence of a stimulus that is irrelevant to a discrimination.

In 5 autoshaping experiments pigeons received 3 stimuli, A, B, and C, for a discrimination in which food was presented after the simultaneous compounds AC and BC, but not after the simultaneous compound ABC. The ease with which this discrimination was mastered was facilitated by presenting C continuously throughout each session (Experiment 1), by presenting C by itself for nonreinforced trials (Experiment 2), and by pairing C by itself consistently with food (Experiment 3). Presenting C by itself and pairing it with food according to a partial reinforcement schedule had no significant influence on the acquisition of the discrimination (Experiments 4 and 5). The results are consistent with a configural theory of associative learning that suggests that experience with a stimulus alters its salience. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Effect of unconditioned stimulus magnitude on the emergence of conditioned responding.

Although unconditioned stimulus (US) magnitude influences conditioning, no experiment has addressed whether it influences a decision point at which the organism first responds (Gallistel & Gibbon, 2000). Two appetitive conditioning experiments with rats confirmed that the rate of food cup entries and proportion of head jerking were related to the number of pellets (US) provided after the conditioned stimulus. In addition, the onset of responding measured by the number of reinforcers to a criterion or by a quantitatively identified change point also reflected US magnitude. Two aversive conditioning experiments also found that the amount and onset of freezing were related to footshock intensity. All experiments identified a trial at which responding increased abruptly in individual subjects. However, the point where the increase occurred was earlier with larger USs. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Potentiation of the acoustic startle response by a conditioned stimulus paired with acoustic startle stimulus in rats.

The hypothesis that the standard acoustic startle habituation paradigm contains the elements of Pavlovian fear conditioning was tested. In a potentiated startle response paradigm, a startle stimulus and a light conditioned stimulus (CS) were paired. A startle stimulus then was tested alone or following the CS. Freezing behavior was measured to index conditioned fear. The startle response was potentiated on CS trials, and rats froze more in CS than in non-CS periods. In Experiment 1, response to a previously habituated, weak startle stimulus was potentiated. In Experiment 2, response to the same stimulus used as the unconditioned stimulus (US) in training was potentiated. This CS-potentiated response retarded the course of response decrements over training sessions as compared with an explicitly unpaired control group. Conditioned fear is a standard feature of this habituation paradigm, serves to potentiate the startle response, and provides an associative dimension lacking in the habituation process per se. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Potentiation or diminution of discrete motor unconditioned responses (rabbit eyeblink) to an aversive Pavlovian unconditioned stimulus by two associative processes: Conditioned fear and a conditioned diminution of unconditioned stimulus processing.

In 2 experiments using the rabbit conditioned eyeblink preparation, the conditions under which a Pavlovian conditioned stimulus/stimuli (CS) potentiates or diminishes the unconditioned response (UCR) were examined. Results indicate that, after discrimination training (CS+ vs CS–), the CS+ diminished UCR amplitude at the training interstimulus interval (ISI). When CS+ trials were segregated into trials on which a conditioned response (CR) did or did not occur, the CS+ diminished the UCR when it elicited a CR, but not when a CR failed to occur. When the CS-unconditioned stimulus (UCS) interval was lengthened to 10 sec, the CS+ reliably potentiated the eyeblink UCR on CR trials but did not potentiate responding on trials on which a CR was absent. Results are discussed in terms of the modulatory effects and temporal properties of conditioned fear and an associatively produced decrement in UCS processing. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Exposure to the unconditioned stimulus alone: Effects on retention and acquisition of conditioned suppression.

In 3 experiments with 104 male Sprague-Dawley rats, repeated exposure to an electric-shock UCS resulted in a decrement in retention of conditioned suppression evoked by a previously established excitatory CS and retarded subsequent acquisition of conditioned suppression to a novel CS paired with shock. Exp I showed that 10 sessions of exposure to shock alone were required to produce a decrement in retention of conditioned suppression, whereas retardation in the acquisition of conditioned suppression was obtained following either 5 or 10 sessions of exposure to shock alone. Exp II demonstrated that both of these effects were directly related to the intensity of the shocks. In Exp III, the decrement in retention of conditioned suppression produced by 10 sessions of exposure to shock alone was inversely related to the interval between the last exposure to shock and the test of the target CS. Findings are discussed in terms of associative and nonassociative accounts of the effects of UCS-alone procedures. (29 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Stimulus control of avoidance behavior in rats following differential or nondifferential Pavlovian training along dimensions of the conditioned stimulus.

Assigned 36 male albino Holtzman rats, following 2-way avoidance training with an auditory CS, to 1 of 6 Pavlovian manipulations: discrimination or equivalence training along frequency or intensity dimensions, nominal single stimulus training, or unsignalled shocks only. Subsequently, Ss received separate generalization tests when frequency and/or intensity were varied. Intradimensional discrimination training tended to steepen generalization gradient and resulted in a peak shift away from the negative CS (safety signal) within the frequency continuum. Pseudodiscrimination equivalence training typically reduced stimulus control, even when training and test stimuli were not along the same dimension. These modifications of avoidance generalization gradients through interpolated noncontingent training provide additional evidence of the transfer of Pavlovian control to instrumental behavior. (35 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Effect of conditioned stimulus intensity on visually conditioned heart rate change in the pigeon: A sensitization mechanism.

In visually conditioned heart-rate change in 30 White Carneaux pigeons, increasing the conditioned stimulus intensity enhanced performance. The effect, which only appeared at high intensity levels, was obtained during acquisition and with rigorous maintenance of constant stimulus conditions. A similar effect was obtained with 10 sensitization control Ss. Evidence is presented that the stimulus intensity effect during conditioning may have totally reflected increased sensitization such that the locus of the effect was upon performance rather than conditioning per se. (18 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Conditioning using a cerebral cortical conditioned stimulus is dependent on the cerebellum and brain stem circuitry.

Electrical stimulation of the auditory cortex (AC) was used as a conditioned stimulus/stimuli (CS) in the rabbit conditioned eyeblink preparation to trace the functional anatomical connections between the AC and the circuitry underlying this conditioned response (CR). Conditioning was shown to be dependent on the cerebellar interpositus nucleus and the pontine nuclei (PN), structures that are essential for conditioning using a peripheral CS. Results suggest that the cerebellum and associated brain stem circuitry are a necessary part of the memory trace circuit for the conditioned eyeblink response, even when the cerebral cortex is artificially engaged as a CS by electrical stimulation. Results also suggest that the PN are a site of convergence between the CS circuit subserving classical conditioning for peripheral stimuli and the AC, and may therefore be a site where the AC can modulate more elaborate forms of conditioning. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Effects of context on responding during a compound stimulus.

In 4 experiments, the authors used rats to examine the strength of responding during a clicker-tone compound in the presence of a light, after the auditory stimuli had individually been paired with food in the presence of the same light. Experiment 1 demonstrated a higher rate of responding during the compound when the duration of the light was short rather than long. In Experiments 2, 3, and 4, the long duration light was used as a signal for food in a conditional discrimination involving the tone and the clicker. Responding on test trials with the clicker-tone compound during the light was enhanced by this treatment and resulted in a level of performance that was no different from that observed when the duration of the light was short. The results are more compatible with a configural than an elemental theory of associative learning. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Familiarity-based stimulus generalization of conditioned suppression in rats is dependent on the perirhinal cortex.

We report that bilateral, excitoxic lesions of the perirhinal cortex attenuate rats' familiarity-based stimulus generalization. After surgery, rats were preexposed either to 2 auditory stimuli (A and B) or to only 1 auditory stimulus (B). Following preexposure, all rats received pairings of A and a footshock before assessment of generalized responding (conditioned suppression) to B. Sham rats' generalization was greater when preexposure was to both A and B than when preexposure was to B only. That pattern was abolished in lesioned rats, though no general deficiency was found in other measures of auditory processing. Our findings suggest that the perirhinal cortex is required for rats to encode familiarity as part of stimulus representations. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Stimulation of the lateral septum is a more effective conditioned stimulus than stimulation of the medial septum during classical conditioning of the eye-blink response.

Eight rabbits were trained in the classically conditioned eye-blink response procedure using stimulation of the septal nuclei as the conditioned stimulus (CS). Each rabbit was trained with both medial septal stimulation and lateral septal stimulation. Stimulation of the medial septum was a far less effective CS than stimulation of the lateral septum. This effect may be due to the different roles of these two nuclei in classical conditioning. Conditioning using lateral septal stimulation as a CS is dependent on the cerebellar interpositus nucleus as is conditioning using peripheral and other brain stimulation CSs. (PsycINFO Database Record (c) 2010 APA, all rights reserved)