Classical conditioning with electrical stimulation of cerebellum as both conditioned and unconditioned stimulus.

Stimulating electrodes were implanted in rabbit cerebellum, providing an electrical conditioned stimulus (CS) activating cortical parallel fibers and thence Purkinje and other cells, and an electrical unconditioned stimulus (US) activating underlying white matter and eliciting unconditioned responses. Paired CS-US presentations led to the development of conditioned responses, which showed extinction following CS-alone trials and reacquisition with significant savings on reinstatement of paired trials. Increased local excitability as a result of paired training (but not following unpaired stimulus presentations) was observed in cerebellar cortex, as manifested in substantial decreases in CS threshold for response elicitation in all subjects. This preparation offers a model for the study of plastic neuronal interactions within cerebellar networks critically involved in associative learning. (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)     

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)     

Modification of unit responses to gustatory stimuli by conditioned taste aversion in rats

Secretion of trypsin, chymotrypsin, lipase and amylase was measured in male rats under urethane anaesthesia using a method of continuous perfusion of the duodenum. Prolonged infusion of cholecystokinin-pancreozymin (CCK-PZ) over a period lasting 200-360 min was administered either alone or together with a submaximal dose of secretin (1 unit/100 g - 10 min). Infusion of CCK-PZ was carried out using maximal doses (1--1.5 unit/100 g - 10 min) with and without secretin. Supramaximal doses of CCK-PZ (2 and 4 units/100 g - 10 min) were used only in combination with secretin. In all experiments secretion of enzymes showed a triphasic pattern including an initial peak followed by a plateau secretion after 10--20 min (phase 1), a decreasing second phase and finally base-line secretion (phase 3), thus demonstrating exhaustion of enzyme output from the gland with time. With increasing and supramaximal dose of CCK-PZ the cumulative output of enzymes from start to baseline secretion decreased progressively. Under the same conditions the levels of peak and plateau secretion were lower, the duration of plateau secretion was longer and the decreasing phase of secretion was shortened. These features indicate inhibition of secretion with increasing supramaximal doses of CCK-PZ infusion. Whereas the proteolytic enzymes and lipase reacted in a parallel way always amylase secretion was sustained on a higher level, implicating an alternative pathway for secretion.     

Septal lesions potentiate freezing behavior to contextual but not to phasic conditioned stimuli in rats.

The effects on freezing behavior elicited by contextual and phasic conditioned stimuli (CSs) were examined in rats with septal lesions. Two wks after surgery, blocks of 2 conditioning trials consisting of a tone (10 kHz, 75 dB, 20 sec) paired with a footshock (500 msec, 0.5 mA) were presented on 2 consecutive days. Tone-alone trials were presented each day thereafter until extinction criterion was met. Septal lesions were found to potentiate the freezing response elicited by contextual stimuli but had no effect on freezing elicited by the phasic CS. The septum thus appears to be involved in the acquisition and/or expression of defensive behaviors elicited by contextual stimuli. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Instructions as discriminative stimuli in verbal conditioning and awareness.

This investigation was to study the effects of preconditioning instructions and type of reinforcer on level of awareness and extent of conditioning. Prior to a conditioning task, Ss in different experimental groups were given varying degrees of information concerning the nature of the reinforcement and the reinforcement contingency. In some groups of Ss the reinforcement consisted of E saying "good" while in other experimental groups the Ss received points as reinforcement. The results indicated that the degree of conditioning and level of awareness were partially dependent upon the amount of information in the preconditioning instruction. However, in experimental groups where only partial information was given, Ss who received points conditioned better than Ss who received "good" even though there were no differences in the level of awareness. The nature of the response class was also found to be an important variable that affected the level of conditioning. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Compound conditioned emotional response conditioning with differentially salient elements in rats.

R. Rescorla and A. R. Wagner's model of conditioning (1972) implies that, if 2 conditioned-stimulus (CS) elements are independently conditioned to asymptote and then compounded, reinforcement of the compound should reduce the conditioned strength of each element. Further, the more salient element should lose more strength and should ultimately show less conditioned strength than the less salient element. 4 groups of 8 male Holtzman albino rats each, in a conditioned emotional response procedure, provided 2 independent tests of this deduction at different levels of CS salience. Data in each case appear consistent with the model's prediction, significantly so in 1 case. Data in other aspects confirm deductions drawn from the model. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Latent inhibition and overshadowing in conditioned emotional response conditioning with rats.

Tested whether unreinforced preexposure to one element of a compound CS would prevent that element from overshadowing the other element, using 64 male hooded COBS rats. Groups of Ss were given 20 preexposure trials to a light prior to conditioned emotional response (CER) conditioning or were given no pre-exposure. In CER conditioning, Ss received either a noise plus light or a noise followed by shock. In Ss given no pre-exposure, the presence of the light significantly attenuated conditioned suppression to the noise CS. However, in the pre-exposed compound-cue group no reduction in suppression to the noise CS was observed after 4 CER trials. After 8 CER trials, suppression to the noise CS was significantly attenuated. Latent inhibition temporarily reduced the extent to which the light CS overshadowed the noise CS. Overshadowing of the noise in the pre-exposed compound-cue group after 8 CER trials was not accompanied by any increase in suppression to the light CS. (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)     

Failure to produce conditioning with low-dose trimethylthiazoline or cat feces as unconditioned stimuli.

Trimethylthiazoline (TMT), a derivative of fox feces, has been reported to fail to produce aversive conditioning as an unconditioned stimulus (UCS) when presented in large amounts. Experiment 1 evaluated very low TMT levels that nonetheless produced defensive behaviors in rats during exposure. Although each level (0.01, 0.05, and 0.10 μl TMT) produced significant change in defensiveness, none resulted in significant changes the following day in the absence of TMT. Experiment 2 evaluated cat urine, cat feces, and cat fur/skin odor against a no-odor control. Urine produced no significant changes, but feces and fur/skin odors elicited virtually identical changes in defensive behaviors during exposure. When tested the next day in the absence of odor, the fur/skin odor-exposed group showed significant differences on the same behaviors as during exposure, but the feces-exposed group showed no differences on any measure. Results suggest that lack of conditioning to TMT may relate to the type of predator odor rather than the amount, predator species, or possible lack of odor components in TMT that are present in natural feces. Predator feces may also be less effective as a UCS because they are poorly predictive of the actual presence of the predator. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Water deprivation enhances fear conditioning to contextual, but not discrete, conditional stimuli in rats.

Water-deprived and nondeprived rats were fear conditioned with a discrete tone CS and an aversive footshock unconditioned stimulus/stimuli (UCS). 24 and 48 hrs following conditioning, conditional fear to the tone CS and the context cues of the conditioning chamber, respectively, were assessed by measuring freezing behavior. Water deprivation had no effect on baseline responding to either tone or contextual stimuli. Following either 1 or 3 tone-shock pairings, however, water deprivation selectively enhanced conditional freezing to the contextual cues of the training chamber; conditional freezing to the tone was unaffected by water deprivation. These results are consistent with the view that water deprivation affects fear conditioning via an influence on the hippocampus. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Enrichment to odors improves olfactory discrimination in adult rats.

The authors tested how prior odor enrichment affects the spontaneous discrimination of both preexposed and novel odors. Experimental rats were exposed to single odors or to pairs of similar or dissimilar odors for 1-hr periods twice daily over 20 days. Spontaneous discriminations between pairs of similar odors were tested before and after the odor exposure period using an olfactory habituation task. The authors found that (a) experimental rats did not spontaneously discriminate similar odor pairs before the exposure period, whereas they spontaneously discriminated them after the enrichment period, and (b) the improvement of performance was not selective for the odors used during enrichment. These results show that odor experience changes perception in the manner predicted based on other groups' electrophysiological experiments. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Hippocampal lesions alter conditioning to conditional and contextual stimuli

The control of conditioned fear behaviour by a conditional stimulus (CS) and contextual stimuli (CXT) was compared in rats with lesions to the hippocampus (HPC) or neocortex (CO), and operated controls (OC). After classical fear conditioning in a distinctive context, rats were subsequently tested in the presence of the CS and CXT (CS + CXT), the CS alone (CS-only), or context alone (CXT-only). Two experiments were conducted in which conditioned fear was measured by an active avoidance response (experiment 1) or by response suppression (experiment 2). Groups did not differ in acquiring the conditioned fear response, as measured in the CS + CON test but, in both experiments, hippocampal (HPC) groups exhibited more conditioned fear behaviour than controls in the CXT-Only and CS-Only conditions. It was suggested that control rats conditioned the fear response to a stimulus complex that incorporated the CS and CTX. Rats with HPC lesions did not form this association between the stimulus elements; instead they segregated the CS and CXT and formed independent associations between the conditioned response (CR) and each component. In showing that HPC damage disrupts the process of forming associations between environmental stimuli and that the effect is not restricted to contextual cues, the results help to resolve apparently contradictory findings regarding the role of HPC in contextual information processing.     

Facial expressions of emotion as conditioned stimuli for human autonomic responses.

Used 26 undergraduates to test the hypothesis that congruity of a facial affective expression with an aversive outcome as compared to incongruity of an expression and outcome would result in superior differential conditioning of an autonomic response (skin conductance) to the facial expression. The study employed a differential conditioning paradigm with slides of fear faces and happy faces and CS+ and CS– or CS– and CS+, respectively. Findings are consistent with predictions. Both magnitude and rate of acquisition of the differential CR were greater when a fear expression was reinforced by shock than when a happy expression was reinforced by shock. (11 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Classical conditioning of environmental cues to cigarette smoking.

Smoking-related cues tend to produce urges and cardiac responses in smokers. This reactivity has been assumed to reflect prior classical conditioning. However, little direct evidence exists supporting the notion that environmental cues can be classically conditioned to cigarette smoking. In this study, 8 smokers received 22 daily trials during which 2 cue complexes (comprising visual, olfactory, and auditory stimuli) were paired with smoking (CS+ trials) and not smoking (CS– trials). Reactivity to the environmental cues, as measured by self-report of urge and pulse rate, increased across CS+ trials, diverging from responses in the CS– trials. Reactivity was stronger among light smokers and those who verbalized awareness of smoking contingencies. Findings indicate that environmental cues can be classically conditioned to smoking. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Some parameters affecting shuttle-box avoidance responding with rats receiving serially presented conditioned stimuli.

Gave 48 male Blue Spruce rats shuttle-box training with serial or nonserial CS procedures. The serial CS condition (S1/S1S2), which involved a single stimulus for the 1st 1/2 of a 16-sec CS-UCS interval and 2 stimuli for the latter 1/2, produced shorter avoidance latencies and more avoidance responses when compared with a serial condition (S1/S2), in which the latter 1/2 of the interval involved only 1 stimulus. Both serial conditions resulted in longer avoidance latencies when compared to nonserial conditions. Exp. II with 144 Ss demonstrated that the above latency differences could be eliminated with shorter CS-UCS intervals, and Exp. III with 72 Ss suggested that avoidance-latency differences obtained at longer CS-UCS intervals were independent of the CS duration ratio between serial components. These and other findings were predicted from a generalization-decrement hypothesis. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Emotional conditioning to masked stimuli: Expectancies for aversive outcomes following nonrecognized fear-relevant stimuli.

The role of conscious awareness in human Pavlovian conditioning was examined in 2 experiments using masked fear-relevant (snakes and spiders; Experiments 1 and 2) and fear-irrelevant (flowers and mushrooms; Experiment 1) pictures as conditioned stimuli, a mild electric shock as the unconditioned stimulus, and skin conductance responses as the primary dependent variable. The conditioned stimuli were presented briefly (30 ms) and were effectively masked by an immediately following masking stimulus. Experiment 1 demonstrated nonconscious conditioning to fear-relevant but not to fear-irrelevant stimuli. Even though the participants could not recognize the stimuli in Experiment 2, they differentiated between masked stimuli predicting and not predicting shocks in expectancy ratings. However, expectancy ratings were not related to the conditioned autonomic response. (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)     

Pavlovian appetitive contingencies and approach versus withdrawal to conditioned stimuli in pigeons.

Investigated the directed skeletal movements of 21 female White Carneaux pigeons toward signals of food or no food in 3 experiments. Ss approached and pecked an illuminated key that was positively correlated with food delivery, and positioned themselves relatively far from an illuminated key that was negatively correlated with food delivery. Key illuminations alone, random presentations of key illuminations and food, and backward pairings of key illuminations and food did not produce keypecking or consistent approach-withdrawal. Therefore, directed skeletal behavior-often believed to be conditioned and maintained primarily or exclusively by operant procedures-also emerges on Pavlovian procedures. Several kinds of alternative explanations (e.g., conditioned reinforcement effects, and stimulus substitution) for these phenomena are considered, and some potential implications for operant discrimination learning are briefly explored. (17 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)