Blocking and unblocking of conditioned analgesia

Two experiments with rat subjects assessed the blocking phenomenon using inhibition of responding to painful thermal stimulation as an index of conditioned analgesia established through conditioned stimulus (CS)-shock pairings. In Experiment 1, a group of rats receiving the standard blocking procedure ($\text{A+}\text{AB+}$) showed shorter response latencies during a hot plate test of pain sensitivity in the presence of the added CS than groups of rats receiving various blocking control procedures. Experiment 2 replicated the blocking outcome of Experiment 1 and also demonstrated that the addition of a second shock unconditioned stimulus (US) during the compound conditioning phase attenuated the blocking effect; i.e., unblocking was observed. However, the deletion of a second shock US during compound conditioning in a group that had received two shocks on each trial in the first phase of the experiment failed to result in unblocking. These data extend the associative account of conditioned analgesia to situations involving stimulus selection and the implications for the analysis of aversive learning are discussed.     

Interactions between conditioned stimuli for food and water in the rat

In two experiments rats were initially trained with one conditioned stimulus (CS) signalling food and another CS signalling water. The main purpose of the experiments was to examine the effects of presenting these stimuli in compound. Experiment 1 demonstrated that the level of conditioned responding to this compound was equal to that of a group for which the compound was composed of elements that had separately signalled the same reinforcer. Moreover, the level of this responding was greater than for a group that had received only compound conditioning. In the second experiment it was found that after the initial training, repeatedly pairing the compound with a single reinforcer resulted in an equivalent loss of conditioned responding to both elements. These findings suggest that the interaction between conditioned stimuli for food and water is facilitatory rather than inhibitory.     

Facilitation and Retardation of Flavour Aversion Conditioning Following prior Exposure to the CS

Two sets of experiments on flavour aversion conditioning in rats examined the effects of the following factors: the nature of the flavour serving as the conditioned stimulus (CS), which was either a compound of monsodium glutamate, sucrose and quinine, or an elemental flavour, either sucrose or dilute acid; the amount of the CS rats consumed on a single conditioning trial-4 ml or 1 ml; and whether rats had been pre-exposed to the CS before this conditioning trial. There were three main findings. First, conditioning to an elemental CS was unaffected by the amount consumed on the conditioning trial, but conditioning to 1 ml of the compound CS was poorer than to 4 ml. Second, pre-exposure produced a latent inhibition effect if the CS was an elemental flavour, or if rats were allowed to drink 4 ml of the compound solution on their conditioning trial. But, third, pre-exposure facilitated conditioning in rats given only 1 ml of the compound solution as their CS.     

Blocking of conditioning of tentacle lowering in the snail (Helix aspersa)

Experiment 1 established the effectiveness of an appetitive conditioning of odours procedure with snails (Helix aspersa) that was subsequently used for the study of blocking. In this important phenomenon, the conditioning of a CS1 (where CS is the conditioned stimulus) prior to conditioning of a compound, CS1CS2, blocked the conditioning to the CS2. Experiments 2a, 2b, and 2c demonstrated this associative effect using three different experimental controls. Experiments 3a and 3b replicated the blocking effect and allowed us to reject an explanation of blocking based on generalized effects of several treatments of diverse stimuli in blocking and control groups (the pseudoblocking effect). The implications of these results for the study of invertebrate cognition by means of conditioning techniques are discussed.     

Contextual conditioning in infants, but not older animals, is facilitated by CS conditioning

Context conditioning in infant Sprague-Dawley rats (postnatal days [PD] 15, 17, and 19), juveniles (PD 25), adolescents (PD 35), and adults (PD 71-89) was compared when CS conditioning did or did not occur in the context. Degree of CS conditioning within that context was equated across age, and separate groups at each age were given unpaired presentations of the CS and US within that context. Infants conditioned more effectively to context when CS-US pairings occurred in that context than when they did not, juveniles conditioned to context about equally with and without CS-US pairings in the context, and adolescents and adults conditioned less effectively to context when CS and US were paired than when unpaired. Adolescents had significant context conditioning despite CS-US pairings in the context but adults did not, and overall, context conditioning was strongest for adolescents. Supplementary experiments indicated that with more extensive conditioning experience, the infants' pattern of context conditioning became more similar to that of older animals, and with less conditioning experience the pattern of context conditioning by adults became more similar to that of younger animals, but infants never attained the adult pattern of context conditioning nor did adults attain the infant pattern. The potentiation of context conditioning by CS conditioning observed in infants is consistent with previous evidence derived from compound conditioning. Alternative explanations place common emphasis on infant-specific amodal processing. One views potentiation as a result of the greater perceived intensity of the stimulus compound (CS and context, in this case) during conditioning and the lesser generalization decrement in infants than adults when tested with a single element after conditioning with a compound. The other explanation emphasizes consequences of the redundancy inherent in intersensory compounds, within the theory of Bahrick and Lickliter.     

Stimulus and temporal cues in classical conditioning

In 2 experiments, separate groups of rats were given stimulus conditioning, temporal conditioning, untreated control and (in Experiment 2) learned irrelevance control procedures, followed by a compound with both stimulus and temporal cues. Stimulus conditioning consisted of a random 15-s duration conditioned stimulus (CS) followed by food; temporal conditioning consisted of food-food intervals of fixed 90 s (Experiment 1) or fixed 75 + random 15 s (Experiment 2). The stimulus group abruptly increased responding after CS onset, and the temporal group gradually increased responding over the food-food interval. When the food-food interval was fixed 90 s, the temporal cue exerted stronger control in the compound, whereas when the food-food interval was fixed 75 + random 15 s, the stimulus cue exerted stronger control. The strength of conditioning, temporal gradients of responding, and cue competition effects appear to reflect simultaneous timing of multiple intervals.     

Summation of reinforcement rates when conditioned stimuli are presented in compound

Three experiments used delay conditioning of magazine approach in rats to examine the summation of responding when two conditioned stimuli (CSs) are presented together as a compound. The duration of each CS varied randomly from trial-to-trial around a mean that differed between the CSs. This meant that the rats' response rate to each CS was systematically related to the reinforcement rate of that CS, but remained steady as time elapsed during the CS (Harris & Carpenter, 2011; Harris, Gharaei, & Pincham, 2011). When the rats were presented with a compound of two CSs that had been conditioned separately, they responded more during the compound than during either of the CSs individually. More significantly, however, in all three experiments, the rats responded to the compound at the same rate as they responded to a third CS that had been reinforced at a rate equal to the sum of the reinforcement rates of the two CSs in compound. We discuss the implications of this finding for associative models (e.g., Rescorla & Wagner, 1972) and rate-based models (Gallistel & Gibbon, 2000) of conditioning.     

The effects of lesions in the central nucleus of the amygdala on appetitive classical conditioning in rats

Abstract: Lesions in the central nucleus of the amygdala (cAMY) have been known to interfere with the acquisition of fear classical conditioning when footshock is used as an unconditioned stimulus (US). The present study examined whether or not a similar interference would occur with an appetitive US. Five rats with lesions in the cAMY (the cAMY group), and eight unoperated control rats were trained in an appetitive classical conditioning paradigm, which did not include elements of operant learning, using a visual conditioned stimulus (CS) (5 W of light for 10 s duration) paired with a food pellet US (45 mg, cheese flavor). The behavioral index of appetitive conditioning was an increase in rearing approach behavior to the CS after CS and US pairings. During CS and US pairings, the movement of the rat was limited so that this approach behavior could not occur. As a result, all control rats showed an increase in rearing, but the cAMY group did not. These results suggest that the cAMY is critical for appetitive as well as fear classical conditioning.     

Effect of posttrial episodes on conditioning in compound conditioned stimuli

The effect of signaled and nonsignaled posttrial episodes (PTEs) on conditioning to the target CS of a preceding compound CS-US trial was examined in two conditioned emotional response (CER) experiments with rats. Experiment 1 revealed that a nonsignaled PTE, a second shock US, interfered with conditioning to the preceding target CS and that the interference effect of the PTE was greater when it occurred 5 sec as opposed to 1,800 sec after the preceding compound CS-US trial. Experiment 2 revealed that if the shock PTE was signaled by a CS, its ability to interfere with conditioning was reduced. This second study also revealed that omission of an "expected" US interfered with conditioning to the target CS. The implications of these data for information processing models of Pavlovian conditioning are discussed.     

Element preexposure, neophobia, and conditioned aversion to a compound flavor stimulus

Preexposure to one or two elements of a compound flavor stimulus greatly reduced a neophobic reaction to the compound but did not attenuate conditioned flavor aversion in rats. Results indicated that (1) a preexposure effect on conditioned aversion to a flavor compound is not likely to be obtained if subjects initially show a strong neophobic reaction to the elements and (2) the level of neophobia at the time of conditioning has little influence on conditioned flavor aversion.     

The effects of language conditioning on various aspects of anxiety

Staats' three-function learning theory provides the basis for investigating the effects of emotionally-relevant self-verbalizations (SV) on the physiological, subjective-affective and behavioural aspects of anxiety. Using aversive electric UCSs and slides of snakes (CS), anxiety was classically conditioned in 88 volunteer Ss. In 20 subsequent language-conditioning trials (without aversive electric UCSs), the same snakes slides were paired with UCS verbalizations having either positive or negative connotative meanings. Half of the Ss were exposed to a living snake prior to language conditioning. The results show a complete extinction of the conditioned anxiety response in groups with positive SV whereas negative SV impeded extinction; the latter effect could only be found in groups without exposure to snakes prior to language conditioning. In general, the affective evaluation of snakes improved in groups with positive SV and deteriorated in groups with negative SV. However, these effects were more pronounced in groups without exposure to snakes. Although the results indicate that Ss in all groups with positive SV exhibited more approach behaviours than Ss with negative SV, this trend was not statistically significant. The possible relevance of the results for a language-conditioning approach to anxiety reduction is briefly discussed.     

对体液免疫反应的条件反射性调节

以饮糖精水作为条件刺激(conditioned stimulus,CS),腹腔注射免疫抑制剂环磷酰胺作为非条件刺激(unconditioned stimulus,UCS)训练Wistar大鼠,3天后腹腔注射卵清蛋白(ovalbunfin,OVA)抗原,观察再次单独条件刺激对原发性体液免疫反应的作用。结果发现．一次CU-UCS结合训练导致CS组大鼠对再现糖精水产生厌恶反应,外周血中抗OVA-IgG抗体水平显著低于UCS组。两次CS-UCS结合训练并多次给予条件刺激后,CS组大鼠抗OVA-IgG的条件性免疫抑制效应与一次CS-UCS结合训练及再次给予一次条件刺激的反应类同。这些结果证明条件刺激增强了环磷酰胺对动物原发性体液免疫反应的抑制作用．这种条件性体液免疫抑制作用是相对稳定和有限度的,不易受条件反射建立参数的影响。     

A Comparative Study of Groups of High and Low Intelligence in Learning a Maze

In accordance with the determination of base-line heart rate and running in an activity wheel, 14 Long-Evans male rats were given ten 30 minute sessions of Immobile-Avoid conditioning followed by 30 minute sessions of Active-Avoid conditioning. Control Ss were yoked to the experimental Ss.

Experimental Ss made significantly fewer responses in the immobile-avoid period and significantly more responses in the active-avoid period than did the yoked control Ss. Heart rate was correlated with skeletal activity both for experimental and control Ss. For experimental Ss, low heart rate was concomitant with a low amount of activity in the immobile-avoid period and high heart rate was concomitant with greater skeletal activity in the active-avoid period.

These results support the position that heart rate is secondary to responses of the somatic-motor system and that heart rate during immobile-avoid or active avoid conditioning is more closely related to the level of somatic-motor activity than to the emotional stress which purportedly motivates instrumental avoidance behavior.     

Effect of prior Pavlovian discrimination training upon learning an operant discrimination

The effect of Pavlovian discrimination training with two stimuli upon subsequent learning of an operant discrimination involving those stimuli was studied. After preliminary lever press training, the lever was removed and thirsty rats received noncontingent pairings between S₁ (a tone or a clicker) and water reinforcements, whereas S₂ (a clicker or a tone) occurred always without reinforcement. This procedure presumably established S₁ as a positive CS for respondent behavior, whereas S₂ was established as an inhibitory CS. Following this training, the lever was reintroduced and the rats were trained on an operant (lever pressing) discrimination involving S₁ and S₂. For the Consistent Ss, S₁ was the S^D and S₂ the S^Δ in the operant discrimination; for the Reversed Ss, S₂ served as S^D and S₁ as S^Δ. The Consistent Ss learned the operant discrimination significantly faster than did the Reversed Ss. The result emphasizes the importance of respondents, conditioned to S^D and S^Δ, which modulate operant performance to these stimuli.     

Configural-like effects observed in the course of second-order conditioning in rats

After receiving first-order CER (conditioned emotional response) conditioning, four groups of rats were exposed to the first-order conditioned stimulus (CS₁) and a new stimulus (CS₂) according to one of three paradigms. For different groups, CS₂ preceded CS₁, was simultaneously compounded with it, or was explicitly unpaired with it. There was evidence of second-order conditioning (SOC) only when CS₂ preceded CS₁, with the effect diminishing when SOC training was continued for a long time. Though suppression to CS₁ extinguished in the course of SOC training, animals which had experienced CS₂ preceding CS₁ suppressed almost completely when later tested with CS₁ alone. This “protection-from-extinction” is formally similar to an analogous effect observed in the simultaneous compound group. Animals appear to “configure” elements of both simultaneous and successive compounds.     

Cholinergic modulation of trace conditioning trained in serial compound: A developmental analysis

In four experiments the effects of serial compound conditioning on responding to a trace-conditioned CS were evaluated using a fear conditioning paradigm. The subjects were 18- and 25-day-old Sprague-Dawley rats, previously shown to exhibit little or no trace fear conditioning. Here, animals as young as 18 days of age were shown to be capable of trace conditioning between a visual CS1 and a shock US, provided the trace interval was filled with a non-target CS2 during serial conditioning trials (CS1-->CS2-->US). To explore cholinergic mechanisms involved in trace and serial conditioning, additional experiments assessed conditioned responding following pre-training administration of the muscarinic receptor antagonist scopolamine. Scopolamine produced a dose-dependent reduction in responding to the trace CS1, regardless of whether subjects were trained with standard trace (CS1-->trace interval-->US) or serial (CS1-->CS2-->US) trials. Responding to CS2 was unaffected by scopolamine. These data suggest that central cholinergic systems are functional in the young animals, but are not normally sufficiently activated by standard trace conditioning procedures. The results suggest that serial compound conditioning can promote trace conditioning in young rats, as it does in adults, perhaps by enhancing cholinergic activity during training. Implications for the late ontogenetic emergence of trace conditioning as it relates to maturation of neural pathways and their role in the potentiating effects of a gap filler are discussed.     

Pavlovian second-order conditioned analgesia

Three experiments with rat subjects assessed conditioned analgesia in a Pavlovian second-order conditioning procedure by using inhibition of responding to thermal stimulation as an index of pain sensitivity. In Experiment 1, rats receiving second-order conditioning showed longer response latencies during a test of pain sensitivity in the presence of the second-order conditioned stimulus (CS) than rats receiving appropriate control procedures. Experiment 2 found that extinction of the first-order CS had no effect on established second-order conditioned analgesia. Experiment 3 evaluated the effects of post second-order conditioning pairings of morphine and the shock unconditioned stimulus (US). Rats receiving paired morphine-shock presentations showed significantly shorter response latencies during a hot-plate test of pain sensitivity in the presence of the second-order CS than did groups of rats receiving various control procedures; second-order analgesia was attenuated. These data extend the associative account of conditioned analgesia to second-order conditioning situations and are discussed in terms of the mediation of both first- and second-order analgesia by an association between the CS and a representation or expectancy of the US, which may directly activate endogenous pain inhibition systems.     

Classical conditioning as a nonstationary,multivariate time series analysis: A spreadsheet model

The implementation of the Gallistel (1990) model of classical conditioning on a spreadsheet with matrix operations is described. The model estimates the Poisson rate of unconditioned stimulus (US) occurrence in the presence of each conditioned stimulus (CS). The computations embody three implicit principles:additivity (of the rates predicted by each CS),provisional stationarity (the rate predicted by a given CS has been constant over all the intervals when that CS was present), andpredictor minimization (when more than one solution is possible, the model minimizes the number of CSs with a nonzero effect on US rate). The Kolmogorov-Smirnov statistic is used to test for non-stationarity. There are no free parameters in the learning model itself and only two parameters in the formally specified decision process, which translates what has been leamed into conditioned responding. The model predicts a wide range of conditioning phenomena, notably: blocking, overshadowing, overprediction, predictive sufficiency, inhibitory conditioning, latent inhibition, the invariance in the rate of conditioning under scalar transformation of CS-US and US-US intervals, and the effects of partial reinforcement on acquisition and extinction.     

Overshadowing and stimulus duration

In 3 experiments, the authors investigated the effect of stimulus duration on overshadowing. Experiments 1 and 2 examined responding to a target conditioned stimulus (CS1) when it was conditioned in compound with a coterminating overshadowing stimulus (CS2) that was longer, shorter, or of the same duration (the long, short, and matched groups, respectively). Equal overshadowing of conditioning to CS1 was obtained in all 3 conditions relative to a control group conditioned to the light alone. There were, however, differences in responding to CS2 as a function of its absolute duration. Experiment 3 examined the contribution of the food-food interval/CS onset-food interval ratio to these findings. In Experiments 1 and 2, the ratio differed for the overshadowing CS but not for the target CS. In Experiment 3, this arrangement was reversed, but the pattern of results remained the same. The implications of these findings for trial-based and real-time models of conditioning are discussed.