Facilitation of instrumental behavior by a Pavlovian appetitive conditioned stimulus.

In Exp I, 16 New Zealand white rabbits were trained to perform an instrumental head-raising response for sucrose reward. A jaw-movement CR was established to a 2-sec CS by pairing it with sucrose; a control stimulus was unpaired with sucrose. Instrumental responding maintained by a VI 40-sec schedule was enhanced during 10-sec presentations of the paired, but not the unpaired, CS. Responding on a VR 15 schedule was unaffected except on trials on which the pre-CS baseline response rate was low; in such cases the paired CS caused a long-lasting acceleration of responding. Noncontingent presentation of the sucrose reinforcer itself briefly suppressed responding but had no long-term effect. In Exp II (6 Ss), a CS that had been conditioned at a 10-sec duration produced the same pattern of effects as in Exp I, indicating that facilitation resulted from CS presentation rather than from the frustrative effects of nonreinforcement of the CS. In Exp III (16 Ss), an inhibitory CS blocked facilitation by the excitatory CS but did not itself affect instrumental responding. (53 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)     

Morphine-conditioned changes in locomotor activity: Role of the conditioned stimulus.

When a multisensory environment was reliably paired with morphine (2 mg/kg) in rats, that environment, in a drug-free test, evoked a hyperactive conditioned response (CR). When an olfactory cue (banana odor) was the only stimulus element reliably paired with morphine, it also elicited a hyperactive CR. However, a gustatory cue (saccharin solution) evoked a hypoactive CR. This taste-elicited decrease in activity was dose dependent; morphine at 2 and 4 mg/kg conditioned hypoactivity, whereas a higher dose (8 mg/kg) did not. A robust conditioned saccharin aversion occurred only at the highest dose of morphine, suggesting disassociation between the hypoactive CR and taste aversion. A taste cue present during context conditioning also prevented either acquisition or expression of the hyperactive CR to the context. The modality of the conditioned stimulus is a critical determinant of the form of the CR in a morphine locomotor conditioning paradigm. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The importance of time as stimulus of conditioned reflex activity.

"The formation of conditioned reflexes to time plays an important part in the systemic activity of the cerebral cortex, in the development of definite periodicity in physiological functions, and in the establishment of rhythmical pattern reactions in the working activity of man. By virtue thereof the question of the cortical mechanisms involved in the process of formation of conditioned reflexes to time acquires considerable theoretical and practical importance." Studies, from Russian laboratories, employing a variety of experimental animals, and man, are cited. Experimental variables are systematically described as well as the many theoretical issues. 34 refs. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Mechanisms of second-order conditioning with a backward conditioned stimulus.

Five conditioned suppression experiments with rats examined the conditions under which backward pairings endow a first-order conditioned stimulus (CSI) with the ability to serve as a secondary reinforcer. Experiments 2-5B found evidence for excitatory second-order conditioning (SOC) if, during first-order pairings, the US-CS I interval was 0 s rather than 3 s. Levels of SOC were comparable after forward and backward pairings (Experiments 1-3), and were unaffected by extinction of CS I after SOC (Experiment 3). These results suggest that forward and backward CSIs support SOC for the same reason, and they call into question the need to invoke any special mechanism such as memory integration. (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)     

Electrodermal activity and schizophrenia: The problem of stimulus intensity modulation.

Recent reviews on electrodermal activity and schizophrenia have cited both hyperreactivity and hyporeactivity in groups of schizophrenics. One problem concerning the interpretation of hyporeactivity is that of stimulus-intensity modulation. This problem is defined, and it is suggested that researchers interested in basic neurophysiological activity of schizophrenics employ a nonstressful experimental procedure. (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)     

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)     

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)     

Heart rate conditioning with pentobarbital as a conditioned stimulus and amphetamine as an unconditioned stimulus.

Injected pentobarbital (PB) into rats 20 min after they were placed in an apparatus where heart rates were recorded. Amphetamine was injected after they were removed from the apparatus 29–30 min later. A Pavlovian conditioned response (CR) began after 3 or 4 trials in the form of a failure of conditioned Ss to show the same decline in heart rate obtained in controls after the PB injection. On later trials, the amphetamine was not injected until 50 min after the PB, and the CR was most obvious during the period 30–50 min after the PB injection. The pharmacological effects of PB were necessary for conditioning because the CR was not obtained (a) when normal saline was substituted for the PB after successful conditioning or (b) when saline was used instead of PB throughout. Because of the speed and effectiveness of the conditioning, we believe the mechanism responsible for it has homeostatic regulation as its natural role. It was puzzling that environmental cues seemed to have a role in the conditioned stimulus complex, because conditioning was not apparent when the drug–drug pairings were administered in the home cage. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Increased spontaneous recovery with increases in conditioned stimulus alone exposures.

A series of experiments used the compound test procedure (Rescorla, 2002) to measure the size of spontaneous recovery of freezing responses by rats to a latently inhibited and/or extinguished conditioned stimulus (CS). The size of recovery was greater: to a pre-exposed and conditioned CS than to a CS just conditioned or just pre-exposed; to an extensively pre-exposed or extinguished CS than to a moderately pre-exposed or extinguished CS; and to a pre-exposed and extinguished CS than to a CS just pre-exposed or just extinguished. These results show that the size of recovery is proportional to the size of the depression produced by CS-alone exposures regardless of whether they occurred before, after, or both before and after conditioning. The results are discussed in terms of some contemporary models of recovery and of the inferences permitted by the use of the compound assessment technique. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Stimulus intensity dynamism: Effect of non-reinforcement of the highest intensity stimulus.

24 naive male albino Sprague-Dawley rats, in 2 groups, received extensive lever-pressing-discrimination training to 4 intensities of auditory stimulation (85, 90, 95, 100 db.); 1 intensity was SDELTA and 3 were SD. For 1 group, the lowest intensity stimulus was nonreinforced; for the other group the highest intensity stimulus was the SDELTA. After 24 days, nonreinforcement in each group was switched to stimulation of the other extreme and performance was assessed for an additional 15 days. Results indicate that (a) during the 1st phase response strength was a positive function of the distance, along the intensity continuum, from the nonreinforced stimulus; (b) after nonreinforcement contingencies were changed, performance was immediately disrupted and tended to be replaced by the functional relation of the initial phase; and (c) SDELTA response rate was positively related to SDELTA intensity. (French summary) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Associations between the discriminative stimulus and the reinforcer in instrumental learning.

In three experiments we examined whether reinforcement of a response in the presence of a discriminative stimulus (S{d}) resulted in associations between the S{d} and the reinforcer. In Experiments 1 and 2, animals were given food pellets contingent on responding in the presence of one S{d}, and sucrose contingent on responding in the presence of a different S{d}. Next, they were trained to make two new instrumental responses, one reinforced with pellets and one with sucrose. Finally, those responses were tested in the presence of S{d}s. The presence of S{d}-reinforcer associations was inferred from the preferential enhancement of the S{d} of performance of the instrumental response trained with the same reinforcer. In Experiment 3 we compared the transfer obtained with an S{d} and a Pavlovian excitor (CS+). Both stimuli showed preferential transfer on the basis of reinforcer identity, but the level of enhancement was lower for the CS+. These results show that the S{d} provides information about the identity of the reinforcer earned by a response in the normal course of instrumental learning. Several ways in which that knowledge might be encoded are discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Pairings of a drug or place conditioned stimulus with lithium chloride produce conditioned sickness, not antisickness.

In different experiments, pairings of a drug (pentobarbital or morphine) or place as the conditioned stimulus (CS) with lithium-induced sickness as the unconditioned stimulus (UCS) were given to rats to produce Pavlovian conditioning. Control rats received unpaired exposures. In the test, each rat was exposed to the CS, injected with lithium, and then offered food. If such pairings produce conditioning of antisickness (i.e., a compensatory response that opposes lithium sickness), then the experimental rats should eat more than the controls. The reverse occurred. Thus, pairings of a drug or place CS with a lithium UCS resulted in conditioned sickness rather than antisickness. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Learned helplessness as conditioned inattention to the target stimulus.

Learned helplessness theory explains the impaired performance that follows exposure to uncontrollable outcomes by assuming learned expectation of response-outcome independence that is transferred between tasks. Recent evidence has shown that introducing a second neutral stimulus, contingent on the offset of the uncontrollable stimulus, removes the subsequent interference. This finding has been claimed to support the view that the interference is a result of conditioned inattention rather than of the expectation of response-outcome independence. The conflicting explanations were examined in a series of 4 experiments, using a total of 202 students (undergraduates and nursing and physiotherapy students), that varied induction procedures (passive exposure or inescapability) and stimulus quality (aversive or nonaversive). All 4 experiments found the predicted interference, but only 1, in which passive exposure was combined with an aversive stimulus, obtained results supporting the conditioned inattention hypothesis. It is concluded that learned helplessness probably involves more than a single mechanism and that the passive exposure procedure may not be appropriate for demonstrating genuine helplessness deficits. (19 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Rats with basolateral amygdala lesions show normal increases in conditioned stimulus processing but reduced conditioned potentiation of eating.

Rats with neurotoxic lesions of basolateral amygdala (ABL) and control rats showed comparable enhancement of attentional processing of a visual stimulus when its predictive value was altered. In contrast, lesioned rats showed less potentiation of eating than did control rats when food was available during presentations of a conditioned stimulus that was previously paired with food. When considered together with previous data, these results indicate a double dissociation between effects of lesions of the ABL and of the amygdala central nucleus on phenomena related to attentional processing and the acquisition of motivational value. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Boosting cholinergic activity in gustatory cortex enhances the salience of a familiar conditioned stimulus in taste aversion learning.

The cholinergic system is important for learning, memory, and responses to novel stimuli. Exposure to novel, but not familiar, tastes increases extracellular acetylcholine (ACh) levels in insular cortex (IC). To further examine whether cholinergic activation is a critical signal of taste novelty, in these studies carbachol, a direct cholinergic agonist, was infused into IC before conditioned taste aversion (CTA) training with a familiar taste. By mimicking the cholinergic activation generated by novel taste exposure, it was hypothesized that a familiar taste would be treated as novel and therefore a salient target for aversion learning. As predicted, rats infused with the agonist were able to acquire CTAs to familiar saccharin. Effects of carbachol infusion on patterns of neuronal activation during conditioned stimulus–unconditioned stimulus pairing were assessed using Fos-like immunoreactivity (FLI). Familiar taste–illness pairing following carbachol, but not vehicle, induced significant elevations of FLI in amygdala, a region with reciprocal connections to IC that is also important for CTA learning. These results support the view that IC ACh activity provides a critical signal of taste novelty that facilitates CTA acquisition. (PsycINFO Database Record (c) 2010 APA, all rights reserved)