Effect of amount of context extinction on revaluation of a target CS

In two experiments using rats in a conditioned lick suppression paradigm the effects of posttraining extinction of the conditioning context on responding to the target conditioned stimulus (CS) which had previously been paired with a footshock was examined in a neutral context. Experiment 1 replicated Marlin's [Learn. Motiv. 13 (1981) 526] observation that this treatment can reduce responding to the target CS. This finding is contrary to other reports that context extinction enhances responding to the target CS. Experiment 2 examined the amount of posttraining context extinction as a variable potentially controlling this effect. It found the mediated extinction effect following one, but not 10 h of context extinction.     

Effect of US identity on elimination and recovery of autoshaped responding with explicitly unpaired and degraded contingency extinction procedures

The depressive effects of noncontingent and explicitly unpaired food unconditioned stimuli (USs) and the recovery from those effects on autoshaped responding were examined in a series of experiments with pigeons. In Experiments 1 and 2, responding to a keylight conditioned stimulus (CS) previously paired with food was depressed equally by explicitly unpaired presentations of either that same food or a different food. Furthermore, responding recovered equally following removal of the explicitly unpaired foods. In contrast, Experiments 3 and 4 showed that noncontingent presentations of a food US depressed responding more to a keylight CS paired with that same food than to a keylight CS paired with a different food. Moreover, removal of the noncontingent foods led to complete recovery but more rapid extinction of responding to the same keylight relative to the different keylight. The implications of these results for understanding the mechanisms underlying depression and recovery of responding following degraded contingency and explicitly unpaired extinction procedures are discussed.     

Appetitive differential conditioning of the rabbit's jaw movement response. Effects of cue similarity and US magnitude

Two experiments examined appetitive differential conditioning of the rabbit's jaw movement response (JMR) in a two-phase procedure. The first phase entailed reinforced training with one conditioned stimulus (CS+), and the second phase involved intermixed presentations of CS+ and an unreinforced stimulus (CS-). In Experiment 1, CS+ was a 600-Hz tone, and CS- was either a 660-, 1,000-, or 2,100-Hz tone. In Experiment 2, the magnitude of the water unconditioned stimulus (US) paired with CS+ was either 1, 3, or 9 ml. The experiments revealed that 1) the level of responding to CS- rose for several days and then declined over the remainder of training; 2) the physical similarity between CS+ and CS- directly affected the level of responding to CS- but had no discernable effect on the level of responding to CS+; and 3) US magnitude positively affected the level of responding to CS+ and, to a lesser extent, CS-. The results are discussed in terms of their implications for Spence's gradient interaction theory and Pavlov's external inhibition hypothesis.     

Repeated extinction and reversal learning of an approach response supports an arousal-mediated learning model

We assessed the effects of repeated extinction and reversals of two conditional stimuli (CS+/CS−) on an appetitive conditioned approach response in rats. Three results were observed that could not be accounted for by a simple linear operator model such as the one proposed by Rescorla and Wagner (1972): (1) responding to a CS− declined faster when a CS+ was simultaneously extinguished; (2) reacquisition of pre-extinction performance recovered rapidly within one session; and (3) reversal of CS+/CS− contingencies resulted in a more rapid recovery to the current CS− (former CS+) than the current CS+, accompanied by a slower acquisition of performance to the current CS+. An arousal parameter that mediates learning was introduced to a linear operator model to account for these effects. The arousal-mediated learning model adequately fit the data and predicted data from a second experiment with different rats in which only repeated reversals of CS+/CS− were assessed. According to this arousal-mediated learning model, learning is accelerated by US-elicited arousal and it slows down in the absence of US. Because arousal varies faster than conditioning, the model accounts for the decline in responding during extinction mainly through a reduction in arousal, not a change in learning. By preserving learning during extinction, the model is able to account for relapse effects like rapid reacquisition, renewal, and reinstatement.     

Relative temporal representations in Pavlovian conditioning

The transfer of relative temporal representations was assessed in a series of three experiments. In each experiment, rats (Rattus norvegicus) received one set of conditioned stimulus (CS) and intertrial interval (ITI) durations in Phase 1 and another set in Phase 2. The ratio between the CS and ITI intervals was either changed or maintained across phases. On the hypothesis that relative temporal representations are learned, groups receiving maintained temporal ratios across phases were expected to display greater change in responding upon encountering the new intervals. When the CS duration decreased across phases, maintaining the temporal ratio did lead to greater change in Day 1 of Phase 2 towards the final pattern of responding. However, when the CS increased across phases, maintaining the temporal ratio across phases did not facilitate adjustment to the new intervals, suggesting that extinction of previously reinforced times induced new learning. These results provide evidence that under some conditions, relative relationships in temporal maps may survive transformation-of-scale, like relative relationships in spatial maps.     

Cardiotonic steroids: potential endogenous sodium pump ligands with diverse function

The highly conserved cardiotonic steroid (CS) binding site present on the ubiquitous membrane sodium pump, sodium, potassium-ATPase, appears to have been conserved by no force other than its capacity to bind CS: a family that includes plant-derived cardiac glycosides and putative endogenous vertebrate counterparts. Binding of ligand is inhibited by increased extracellular potassium. This implies functional coordination because inhibition of the sodium pump would be counterproductive when extracellular potassium is elevated. The interesting biology of the CS binding site continues to stimulate investigations into the identity of endogenous ligands, their role as pump regulators at the cellular level, and as mediators of body fluid balance and blood pressure regulation. In addition to inhibition of sodium and potassium transport, there is considerable recent evidence suggesting that the sodium pump may act as a cell signaling receptor activated by CS binding and responding by coordination of intracellular signaling pathways that can be dependent on and also independent of the reduction in transmembrane ion flux resulting directly from pump inhibition. This signaling may influence cell survival, growth, and differentiation. Recent insight into the biology of pump regulation by CS is reviewed.     

Autoshaping in the rat: conditioned licking response to a stimulus that signals sucrose reinforcement

The present experiments were designed to determine if repeated presentations of an empty sipper tube (the conditioned stimulus or CS) with the response-independent delivery of a sucrose solution (the unconditioned stimulus or US) from a second spout results in the development of Pavlovian conditioned responding. In Experiment 1, rats in the experimental condition received paired CS-US presentations whereas subjects in the control condition were exposed to random presentations of CS and US. In Experiment 2, an additional control condition (CS alone) was included and, to encourage generalized responding between the US and CS, the CS tube was filled with water for all groups. The results of both experiments indicate that the CS-directed responding in the paired CS-US condition was Pavlovian in nature. Thus, the present procedure serves as an autoshaping task in which conditioned licking is generated.     

Effects of prefeeding, extinction, and distraction during sample and comparison presentation on sensitivity to reinforcer frequency in matching to sample

The present experiment examined the effects of several test manipulations on discrimination, accuracy and sensitivity to reinforcer frequency in a conditional discrimination. Four pigeons responded on a multiple schedule of matching to sample procedures in which the reinforcer-frequency ratio for correct comparison choice responding was varied across components within session from 1:9 to 9:1. Following stability, the effects of prefeeding, extinction, and distraction during sample and comparison presentation were assessed. Discrimination accuracy decreased under prefeeding, extinction, and distraction during sample presentation. Sensitivity to reinforcer frequency decreased under prefeeding and extinction. Decreases in sensitivity were positively related to decreases in discrimination accuracy. The decreases in discrimination accuracy and sensitivity under prefeeding and extinction are interpreted as being due to decreases in attending to the sample and comparison stimuli, respectively, possibly mediated by motivational effects of these manipulations. This interpretation is consistent with current conceptualizations of the contingencies that govern conditional-discrimination performance.     

The consequences of surrendering a degree of freedom to the participant in a contingency assessment task

Many studies of contingency judgments have used a task in which, on each trial, the participant is free either to respond or not to respond, and an outcome may, or may not, be presented. Typically, the experimenter specifies a nominal value for the contingency between responding and outcome, but the actual values of a variety of variables experienced by a particular participant depend on that participant's frequency of responding. The results of computer simulations of various strategies for implementing the contingency manipulation, and the results of an experiment, indicate that the same nominal contingency value will lead to considerable variability in the actual contingency experienced by participants. Moreover, nominal contingency manipulations are confounded with the probability that the subject experiences an outcome. While researchers might be aware of these issues, not enough attention has been paid to their potential impact.     

Orexin受体1对摄食条件反射的调控研究

目的:观察Orexin受体1对摄食条件反射的调控研究。方法:将40只大鼠随机分为四组,分别为NS/NS组,SB/SB组,NS/SB组,SB/NS组,每组10只大鼠,给予大鼠八组"条件刺激-无条件刺激(CS-US)"训练,给予无条件刺激后立即进行条件刺激,每组进行训练前30 min给予SB或生理盐水(NS)。获得性训练后,给予2组反射消失性训练,即给予8次条件刺激。条件刺激是给予大鼠10 s,2kHZ声音刺激,无条件刺激是直接给予大鼠食物。结果:给予条件刺激后,四组大鼠摄食行为均明显增加,摄食间隔均明显缩短,当条件刺激强度增加时,摄食行为也增加,而预先给予SB,与NS/NS组相比,其余组大鼠摄食行为相对减少(P0.05),摄食间隔增加。消失性训练中,与NS/NS,NS/SB组相比,SB/NS组和SB/SB组大鼠摄食行为明显减少(P0.05)。与其他三组大鼠相比,SB/NS组大鼠摄食间隔缩短。预先给予SB使后两次刺激后摄食间隔明显增加(P0.05)。结论:OX1R信号通路调控摄食反射的产生和消失。     

Selection of trait combinations through bee and fly visitation to flowers of Polemonium foliosissimum

Pollinators are known to exert natural selection on floral traits, but the extent to which combinations of floral traits are subject to correlational selection (nonadditive effects of two traits on fitness) is not well understood. Over two years, we used phenotypic manipulations of plant traits to test for effects of flower colour, flower shape and their interaction on rates of pollinator visitation to Polemonium foliosissimum. We also tested for correlational selection based on weighting visitation by the amount of conspecific pollen delivered per visit by each category of insect visitor. Although bumblebees were the presumed pollinators, solitary bees and flies contributed substantially (42%) to pollination. In manipulations of one trait at a time, insects visited flowers presenting the natural colour and shape over flowers manipulated to present artificial mutants with either paler colour or a more open or more tubular flower. When both colour and shape were manipulated in combination, selection on both traits arose, with bumblebees responding mainly to colour and flies responding mainly to shape. Despite selection on both floral traits, in a year with many bumblebees, we saw no evidence for correlational selection of these traits. In a year when flies predominated, fly visitation showed a pattern of correlational selection, but not favouring the natural phenotype, and correlational selection was still not detected for expected pollen receipt. These results show that flower colour and shape are subject to pollinator‐mediated selection and that correlational selection can be generated based on pollinator visitation alone, but provide no evidence for correlational selection specifically for the current phenotype.     

Intertrial interval as a contextual stimulus

Four experiments with rats investigated whether the time between appetitive conditioning trials can serve as a discriminative cue for responding during the next conditional stimulus (CS). In Experiment 1, rats that received extinction trials with a 4-min intertrial interval (ITI) showed spontaneous recovery after a retention interval of 16 min, whereas rats that received extinction with a 16-min ITI did not. Experiments 2 and 3 investigated more explicit discriminations between the 4- and 16-min ITIs. When a 16-min ITI signaled that the CS would be reinforced and a 4-min ITI signaled that it would not, the ITIs modulated responding to the CS. But when the 4-min ITI signaled reinforcement and the 16-min ITI did not, there was less evidence of modulation by the ITIs. This asymmetry was due at least partly to a difficulty in performance rather than learning. Experiment 4 investigated similar discriminations with 1- and 4-min ITIs. Here the results took a different form: time in the reinforced ITI elicited responding directly, but did not modulate responding to the CS. ITI can function as a contextual cue, and the results suggest new similarities between the processes behind interval timing and associative learning.     

Contextual fear conditioning differs for infant, adolescent, and adult rats

Contextual fear conditioning was tested in infant, adolescent, and adult rats in terms of Pavlovian-conditioned suppression. When a discrete auditory-conditioned stimulus (CS) was paired with footshock (unconditioned stimulus, US) within the largely olfactory context, infants and adolescents conditioned to the context with substantial effectiveness, but adult rats did not. When unpaired presentations of the CS and US occurred within the context, contextual fear conditioning was strong for adults, weak for infants, but about as strong for adolescents as when pairings of CS and US occurred in the context. Nonreinforced presentations of either the CS or context markedly reduced contextual fear conditioning in infants, but, in adolescents, CS extinction had no effect on contextual fear conditioning, although context extinction significantly reduced it. Neither CS extinction nor context extinction affected responding to the CS–context compound in infants, suggesting striking discrimination between the compound and its components. Female adolescents showed the same lack of effect of component extinction on response to the compound as infants, but CS extinction reduced responding to the compound in adolescent males, a sex difference seen also in adults. Theoretical implications are discussed for the development of perceptual-cognitive processing and hippocampus role.     

The “lunching” effect: Pigeons track motion towards food more than motion away from it

Four experiments measured pigeons’ pecking at a small touch-screen image (the CS) that moved towards or away from a source of food (the US). The image's effectiveness as a CS was dependent on its motion, direction, and distance relative to the US. Pecking to the CS increased with proximity to the US when the CS moved towards the US (Experiment 1). This held true even when a departing CS signalled a US of greater magnitude (Experiment 2). Response rates to stationary stimuli were greater the closer they were to the hopper; but rate was less than when the same spot was part of a motion towards food, and greater than when it was part of a motion away (Experiment 3). The rate of responding in all three cases (motion towards, stationary, motion away) decreased exponentially with distance from the hopper. The distance and motion effects observed under these Pavlovian contingencies were different when pecking to the spot was required for reinforcement (Experiment 4).     

Effects of partial reinforcement and time between reinforced trials on terminal response rate in pigeon autoshaping

Partial reinforcement often leads to asymptotically higher rates of responding and number of trials with a response than does continuous reinforcement in pigeon autoshaping. However, comparisons typically involve a partial reinforcement schedule that differs from the continuous reinforcement schedule in both time between reinforced trials and probability of reinforcement. Two experiments examined the relative contributions of these two manipulations to asymptotic response rate. Results suggest that the greater responding previously seen with partial reinforcement is primarily due to differential probability of reinforcement and not differential time between reinforced trials. Further, once established, differences in responding are resistant to a change in stimulus and contingency. Secondary response theories of autoshaped responding (theories that posit additional response-augmenting or response-attenuating mechanisms specific to partial or continuous reinforcement) cannot fully accommodate the current body of data. It is suggested that researchers who study pigeon autoshaping train animals on a common task prior to training them under different conditions.     

Comparative study of perturbations of peripheral markers in different stressors in rats

Stress has been implicated in the etiopathogenesis of several diseases. In the present study, the effects of acute (AS), chronic (CS), and chronic unpredictable stress (CUS) were studied on the ulcer index, adrenal gland mass, and biochemical and hormonal changes in rats. The stress was provided in the form of immobilization-immobilization for 150 min, once only, and for 10 consecutive days in CS and CUS. In CUS, animals received variable unpredictable stressors. Immediately after stress, animals were decapitated, blood was collected, and plasma was separated for the estimation of plasma glucose, triglyceride, cholesterol, creatine kinase (CK), corticosterone, and insulin. The adrenal gland and stomach were also dissected for mass and ulcer scoring, respectively. AS significantly increased the ulcer index, plasma glucose, CK, corticosterone, and insulin. CS and CUS significantly increased the ulcer index, adrenal gland mass, and corticosterone. In CS, a significant decrease in plasma triglyceride and cholesterol levels was found, but in CUS only cholesterol was decreased significantly. High CK activity and hyperglycemia maintain the energy demands of metabolism, and elevated corticosterone desensitizes the insulin receptor in AS. In CS and CUS, prolonged elevation of corticosterone shifts metabolism to utilization of lipids as a secondary substrate by gluconeogenesis. From our experiment, it is clear that AS causes maximum activation of energy metabolism, which becomes specific after habituation in prolonged CS. These biochemical manipulations in the body by using different types of stressors are good markers that can be of great use to understand, target, and manage stress-induced etiologies.     

A Procedure to Observe Context-induced Renewal of Pavlovian-conditioned Alcohol-seeking Behavior in Rats

Environmental contexts in which drugs of abuse are consumed can trigger craving, a subjective Pavlovian-conditioned response that can facilitate drug-seeking behavior and prompt relapse in abstinent drug users. We have developed a procedure to study the behavioral and neural processes that mediate the impact of context on alcohol-seeking behavior in rats. Following acclimation to the taste and pharmacological effects of 15% ethanol in the home cage, male Long-Evans rats receive Pavlovian discrimination training (PDT) in conditioning chambers. In each daily (Mon-Fri) PDT session, 16 trials each of two different 10 sec auditory conditioned stimuli occur. During one stimulus, the CS+, 0.2 ml of 15% ethanol is delivered into a fluid port for oral consumption. The second stimulus, the CS-, is not paired with ethanol. Across sessions, entries into the fluid port during the CS+ increase, whereas entries during the CS- stabilize at a lower level, indicating that a predictive association between the CS+ and ethanol is acquired. During PDT each chamber is equipped with a specific configuration of visual, olfactory and tactile contextual stimuli. Following PDT, extinction training is conducted in the same chamber that is now equipped with a different configuration of contextual stimuli. The CS+ and CS- are presented as before, but ethanol is withheld, which causes a gradual decline in port entries during the CS+. At test, rats are placed back into the PDT context and presented with the CS+ and CS- as before, but without ethanol. This manipulation triggers a robust and selective increase in the number of port entries made during the alcohol predictive CS+, with no change in responding during the CS-. This effect, referred to as context-induced renewal, illustrates the powerful capacity of contexts associated with alcohol consumption to stimulate alcohol-seeking behavior in response to Pavlovian alcohol cues.     

Effects of an extinguished CS on competition with another CS

Three experiments were conducted using a conditioned taste aversion procedure with rats to examine the effect of nonreinforced presentations of a conditioned stimulus (CS) on its ability to compete with a target stimulus for manifest conditioned responding. Two CSs (A and B) were presented in a serial compound and then paired with the unconditioned stimulus. CS A was first paired with the US and then presented without the US (i.e., extinction) prior to reinforced presentation of the AB compound. Experiment 1 showed that A was poor at competing with B for conditioned responding when given conditioning and extinction prior to reinforcement of AB relative to a group that received both A and B for the first time during compound conditioning. That is, an extinguished A stimulus allowed greater manifest acquisition to B. Experiment 2 found that extinction treatment produced a poor CR to the pretrained and extinguished CS itself following compound conditioning. Experiment 3 found that interposing a retention interval after extinction of A and prior to compound conditioning enhanced A's ability to compete with B. The results of these experiments are discussed with regard to different theories of extinction and associative competition.     

Effects of corticotropin-releasing factor (CRF), tuftsin and dermorphin on behavior of squirrel monkeys maintained by different events

The effects of intracerebroventricular (ICV) administration of ovine CRF (0.1–30.0 μg/kg), dermorphin (0.3–30.0 μg/kg) and tuftsin (10–3000 μg/kg) were examined in squirrel monkeys trained to respond under a multiple 3-min fixed-interval schedule of food presentation and either shock presentation or stimulus-shock termination. Initial administration of the 41-amino acid polypeptide CRF increased food-maintained responding by 150–200% in 2 of 3 subjects. However, no other doses tested affected response rates, a result that may have been due to the rapid development of tolerance. The tetrapeptide tuftsin selectively increased responding maintained by food presentation at doses that decreased shock-maintained responding. The heptapeptide dermorphin selectively increased food-maintained responding when responding in the other component of the multiple schedule was maintained by shock presentation. When responding was maintained by a multiple food, stimulus-shock termination schedule, dermorphin decreased response rates in both components. Dermorphin's rate increases were blocked by the opiate antagonist naloxone, indicating that dermorphin's actions were mediated through the opiate receptor. These results indicate that the behavioral effects of tuftsin, dermorphin, and perhaps CRF, depend on the manner in which responding is controlled by its consequences. While the actions of tuftsin and dermorphin are believed to be mediated through the opiate system, the behavioral effects observed in primates appear different from the effects of morphine under similar schedule conditions.     

Rapid acquisition of preference in concurrent schedules: effects of reinforcement amount

Four pigeons were trained on concurrent variable-interval 30-s schedules. Relative reinforcer amounts arranged across the two alternatives were varied across sessions according to a pseudorandom binary sequence [cf., Hunter, I., Davison, M., 1985. Determination of a behavioral transfer function: white-noise analysis of session-to-session response-ratio dynamics on concurrent VI schedules. J. Exp. Anal. Behav. 43, 43-59]; the ratios (left/right) were either 1/7 or 7/1. Reinforcer amount was manipulated by varying the number of 1.2s hopper presentations. Sessions ended after 30 reinforcers (15 for each alternative). After approximately 30 sessions, response ratios for all pigeons began to track the changes in amount ratio (i.e., subjects' responding showed a moderate increase in sensitivity of responding to reinforcer amount). Characteristics of responding were similar to procedures in which reinforcer rate and immediacy have been manipulated, although sensitivity estimates for amount were lower than those previously obtained with rate and immediacy. This procedure may serve as a useful method for studying the effects of certain environmental manipulations (e.g., drug administration) on sensitivity to reinforcer amount.