Recovery of Pavlovian sign-tracking (autoshaping) following the discontinuation of inter-trial interval food in rats

In pigeons, Pavlovian autoshaped keypecking produced by keylight-food pairings has been eliminated by introducing food during periods between CS presentations (i.e., during the inter-trial intervals). Keypecking eliminated in this manner reappears when the inter-trial USs are discontinued even though the CS is no longer paired with US. The present experiment investigated whether this recovery of responding produced by discontinuing unpaired inter-trial US presentations could be extended to another species, rats, within a Pavlovian sign-tracking paradigm. Rats were initially trained on a procedure where insertion of one retractable lever (CS(+)) was followed, response independently, with food, while insertion of another lever (CS(-)) was not paired with food. Rats quickly came to contact the CS(+) lever at high rates, but contacted the CS(-) lever infrequently. In the next phase, CS(+) was no longer followed by food. Explicitly unpaired food was presented only during the inter-trial intervals when both levers were absent. This treatment essentially eliminated the sign-tracking response. In the final phase, the unpaired inter-trial food presentations were discontinued while both CSs continued to be presented without food. This produced a significant recovery of the sign-tracking elicited by the CS(+) lever, extending the species generality of the Pavlovian resurgence phenomenon that has previously only been reported in pigeons, to rats.     

Conditioning of stress in Nile tilapia

A Pavlovian conditioning paradigm was used to induce a connection between a conditioned stimulus, light (CS), associated with an unconditioned stimulus, confinement (US) in Nile tilapia Oreochromis niloticus , which resulted in a conditioned endocrine response (CR) to the CS alone manifested as an increase in plasma cortisol. Individual isolated Nile tilapia were submitted for 10 days to the conditioning treatment consisting of turning on a light (CS) for 1 min with subsequent 30 min confinement (US). On the 10th day of the experiment, plasma cortisol was not increased when fish were subjected to no handling at all, or only light, or even a daily stressor for the 9 days. On the other hand, at the 10th day cortisol was significantly increased only when light was presented either with or without pairing with the stressor. These results confirmed that the cue, light (CS), was not stressful in itself, but when given as the CS in the absence of the US post conditioning the hypothalamus–pituitary–interrenal axis was activated. Therefore, it was concluded that memory of a previous experience with a stressor can be recalled by a conditioned stimulus and induce stress, which is the first demonstration of a memory‐induced stress in fishes.     

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).     

Reaction time task as unconditional stimulus. On conditioning skin conductance responses and heart rate, using a nonaversive unconditional stimulus

The present study was conducted to demonstrate classic conditioning in electrodermal (ED) and heart rate (HR) responses by using a nonaversive reaction time (RT) task as unconditional stimulus (US). Three groups of 12 subjects each were studied to test the efficacy of this US procedure by varying the essential components of the RT task-US between groups. Eight seconds differential delay conditioning was applied in each group. Simple geometric features (square, cross) displayed on a TV screen were used as CS+ and CS-. RT task consisted of a nonaversive tone (72 dBA, 1000 or 1200 Hz) and a motor response (pressing a button with the left index finger). Subjects were asked to respond as soon as the tone stimulus was presented. The three groups received different stimulus sequences during the 16-trial acquisition phase only. In one group (Group C1), CS+ was followed by a tone to which subjects were to respond, whereas CS- was not followed by a tone. Similarly, in a second group (Group H), CS+ was followed by a tone, whereas CS- was not; however, subjects of Group H (habituation group) were not required to respond to the tone. In a third group, (Group C2) CS+ was followed by a tone to which subjects were to respond, while CS- was followed by a different tone requiring no response. According to analysis of Group C1 data, differential conditioning was obtained in each response measure. Group H displayed habituation in each response measure obtained. In Group C2, differential conditioning was obtained in the second latency window of ED responses only.(ABSTRACT TRUNCATED AT 250 WORDS)     

A simple, single, trial-learning paradigm for conditioned increase in natural killer cell activity.

A change in natural killer (NK) cell activity can be conditioned with one trial learning when conditioned stimulus (CS) precedes the unconditioned stimulus (US). To avoid the problems associated with two reexposures in our earlier studies, we have developed a reliable and simple conditioning protocol utilizing the one trial learning and one reexposure to the odor CS. The conditioned change in NK cell activity was significantly different (P less than 0.05) from the control groups of mice. The paradigm is short and simple in that the conditioned change could be demonstrated within 3 days. We have also compared the effects of temporal association of CS and US on conditioned increase in NK cell activity. Forward conditioning (CS preceded the US) demonstrated a conditioned change, but the backward conditioning protocol did not. The paradigm provides a reliable approach to the study of mechanisms of the phenomenon of odor-NK conditioning.     

桔小实蝇雄成虫联系性嗅觉学习

【目的】为了探究桔小实蝇 Bactrocera dorsalis (Hendel)雄成虫的嗅觉学习能力。【方法】本研究采用经典性嗅觉条件反射训练法（classical olfactory conditioning）在室内对固定的羽化后14-17日龄的桔小实蝇雄成虫进行气味与食物的联合学习训练, 即薄荷精油和10%蔗糖溶液联合的奖赏性训练（appetitive conditioning）以及甲基丁香酚(methyl eugenol, ME)和饱和盐溶液联合的惩罚性训练（aversive conditioning）,并以伸喙反射行为（proboscis extension reflex, PER）作为学习与否的判定标准。【结果】经过奖赏性训练后,桔小实蝇雄成虫对薄荷精油的伸喙反射率可从0%增加至68%;而经过惩罚性训练后,桔小实蝇对甲基丁香酚的伸喙反射率可从100%降低至36.54%,且这种伸喙反射率的变化是通过气味条件刺激（conditioned stimulus）和食物非条件刺激（unconditioned stimulus）的对称性联合而产生的。【结论】结果表明,桔小实蝇雄性成虫具有较强的联系性嗅觉学习能力,并且两种刺激的联合是形成学习记忆的必要条件。     

Exposure to cold: aversive Pavlovian conditioning in individual Drosophila melanogaster

Abstract. Temperature changes can be especially threatening for ectotherms, such as Drosophila melanogaster (Diptera: Drosophilidea Meigen, 1830 ), and in this study we tested whether flies can associate olfactory stimuli with a sudden drop in temperature. Such Pavlovian conditioning would allow them to make appropriate behavioural and/or physiological responses in the future. We found that exposing individual flies to one of two odours in the presence of a sudden drop in temperature resulted in Pavlovian conditioning with flies subsequently avoiding the odour paired with cold. The characteristics of Pavlovian conditioning in flies were comparable to those observed for mammalian species. Specifically, the strength of conditioning increased with increasing intensity of the cold and decreased as the time interval between the olfactory stimulus (CS) and cold (US) was lengthened. Finally, the order in which CS and US were presented affected the strength of conditioning. Learning was observed when the CS preceded US and when the US immediately preceded the CS, but not when the CS preceded the US by 30 s or more. These results provide further evidence for learning in individual flies, and confirm that Pavlovian conditioning is a general mechanism used by organisms to obtain information about their environment.     

Accounting for Negative Automaintenance in Pigeons: A Dual Learning Systems Approach and Factored Representations

Animals, including Humans, are prone to develop persistent maladaptive and suboptimal behaviours. Some of these behaviours have been suggested to arise from interactions between brain systems of Pavlovian conditioning, the acquisition of responses to initially neutral stimuli previously paired with rewards, and instrumental conditioning, the acquisition of active behaviours leading to rewards. However the mechanics of these systems and their interactions are still unclear. While extensively studied independently, few models have been developed to account for these interactions. On some experiment, pigeons have been observed to display a maladaptive behaviour that some suggest to involve conflicts between Pavlovian and instrumental conditioning. In a procedure referred as negative automaintenance, a key light is paired with the subsequent delivery of food, however any peck towards the key light results in the omission of the reward. Studies showed that in such procedure some pigeons persisted in pecking to a substantial level despite its negative consequence, while others learned to refrain from pecking and maximized their cumulative rewards. Furthermore, the pigeons that were unable to refrain from pecking could nevertheless shift their pecks towards a harmless alternative key light. We confronted a computational model that combines dual-learning systems and factored representations, recently developed to account for sign-tracking and goal-tracking behaviours in rats, to these negative automaintenance experimental data. We show that it can explain the variability of the observed behaviours and the capacity of alternative key lights to distract pigeons from their detrimental behaviours. These results confirm the proposed model as an interesting tool to reproduce experiments that could involve interactions between Pavlovian and instrumental conditioning. The model allows us to draw predictions that may be experimentally verified, which could help further investigate the neural mechanisms underlying theses interactions.     

Differential resurgence and response elimination

Resurgence refers to the transient recovery of previously reinforced, but presently not reinforced, responding when more recently reinforced responding is extinguished. The primary purpose of our research was to determine how differential resurgence results from the procedures used to eliminate that responding. There were three conditions in each of five experiments. In Condition 1, key pecking by pigeons was maintained under a two-component multiple variable-interval (VI) 30-s VI 30-s schedule. In Condition 2, this pecking was eliminated in different ways across components. In Condition 3, extinction was in effect for all responses, and resurgence of key pecking was compared across components. These three conditions were repeated for most pigeons, and the procedures used to eliminate responding in Condition 2 varied across experiments. In Experiment 1, there was greater resurgence, and an earlier onset of it, after a differential-reinforcement-of-other-behavior (DRO) schedule than after a VI schedule was correlated with pecking an alternative key. Experiments 2 and 3 showed that the differential resurgence in Experiment 1 probably was not due to conditional stimulus control or the periodicity of food delivery, respectively. In Experiment 4, there was no systematic difference in resurgence after either a DRO schedule or a VI schedule correlated with treadle pressing. In Experiment 5, there was greater resurgence, and/or an earlier onset of it, after a VI schedule correlated with treadle pressing than after a VI schedule correlated with pecking an alternative key. Taken together, the results showed that the reinforcement of an alternative key-peck response was the most effective means of reducing subsequent key-peck resurgence. The relation of these results to an understanding of resurgence is discussed.     

Characterizing psychophysical measures of discrimination thresholds and the effects of concentration on discrimination learning in the moth Manduca sexta

What is the spatial and temporal nature of odor representations within primary olfactory networks at the threshold of an animal's ability to discriminate? Although this question is of central importance to olfactory neuroscience, it can only be answered in model systems where neural representations can be measured and discrimination thresholds between odors can be characterized. Here, we establish these thresholds for a panel of odors using a Pavlovian paradigm in the moth Manduca sexta. Moths were differentially conditioned to respond to one odor (CS+) but not another (CS-) using undiluted odorants to minimize salience-dependent learning effects. At 24 and 48 h postconditioning, moths were tested for the presence of a conditioned response (CR) with a blank, then the CS+ and CS- (pseudorandomly) across a 5-log step series of increasing concentration. Results identified discrimination thresholds and established that differential CRs to the CS+ and CS- increased with stimulus concentration. Next, 3 separate groups of moths were differentially conditioned at either one-log step below, at, or one log step above the identified discrimination threshold. At 24 and 48 h postconditioning, moths were tested sequentially with a blank, the concentration used for conditioning, and then undiluted odor. Conditioning at one log step below the discrimination threshold established a CR, indicating both stimulus detection and learning, but was insufficient to establish evidence of discrimination. Moths conditioned at the discrimination threshold were able to discriminate but only when stimulated with undiluted odors, indicating learning, but discrimination measures were hampered. When conditioned above the discrimination threshold, moths had no difficulty in discriminating. These results establish methods for psychophysical characterization of discrimination and indicate that differential conditioning at lowered concentrations biases threshold measures.     

Memorization of contextual and CS conditioned fear response (freezing) in a one-trial acquisition paradigm.

In fear-conditioned Wistar rats freezing was induced by the delivery of a series of footshocks paired to tones (CS) in a specific conditioning chamber (context). CS and contextual fear were acquired in the same single conditioning session without preexposition to the conditioning chamber (day 1). Different groups of animals were conditioned employing three increasing US (footshock) intensities (0.25, 0.5, 0.75 mA). During the retention sessions context and CS conditioned freezing (fear response) were measured using a paradigm that fulfilled the following conditions: i) CS freezing retention was measured in a context different from the conditioning one; ii) CS and context freezing were measured at increased delays after the training session (days 3 and 4, 14 and 15, 28 and 29). The results show that there are significant differences between CS and context freezing retention, which are clearly related to delay after the initial session and to US intensity. In particular: 1) conditioned freezing to a discrete tone is better retained than conditioned freezing to context (irrespective of US intensity); 2) context freezing is directly related to US intensity much more than to tone freezing; 3) context freezing is easier to extinguish than tone freezing. The results are discussed in relation to previous ones and to their relevance to freezing genesis neural correlates.     

Intrusion of stereotyped responding in pigeon spatial memory tasks

Pigeons appear predisposed to respond in stereotyped manners in multi-item spatial memory tasks in which the items are simultaneously presented. We discovered this when we attempted to study primacy and recency serial position effects using a delayed matching of key location task (Experiment 1) and when we attempted to develop a keypack analog of the radial-arm maze task (Experiment 4). In Experiment 1 matching accuracy for first-pecked sample was above chance, approximately chance for the second-pecked sample, and below chance for the third-pecked sample. Experiments 2 and 3 showed that the results of Experiment 1 were due to “superstitious” stereotyped responding: When pigeons were allowed to respond to two or three keys in any order and then respond to the same keys again, they responded in the same order on the second occasion. In Experiment 4, the pigeons successfully avoided pecking previously-pecked keys but did so by pecking the keys in a fixed sequence.     

Towards a unified model of pavlovian conditioning: short review of trace conditioning models

There are three basic paradigms of classical conditioning: delay, trace and context conditioning where presentation of a conditioned stimulus (CS) or a context typically predicts an unconditioned stimulus (US). In delay conditioning CS and US normally coterminate, whereas in trace conditioning an interval of time exists between CS termination and US onset. The modeling of trace conditioning is a rather difficult computational problem and is a challenge to the behavior and connectionist approaches mainly due to a time gap between CS and US. To account for trace conditioning, Pavlov (Conditioned reflexes: an investigation of the physiological activity of the cerebral cortex, Oxford University Press, London, 1927) postulated the existence of a stimulus “trace” in the nervous system. Meanwhile, there exist many other options for solving this association problem. There are several excellent reviews of computational models of classical conditioning but none has thus far been devoted to trace conditioning. Eight representative models of trace conditioning aimed at building a prospective model are being reviewed below in a brief form. As a result, one of them, comprising the most important features of its predecessors, can be suggested as a real candidate for a unified model of trace conditioning.     

Adaptive timing in neural networks: The conditioned response

A conditioned response not only reflects knowledge of an association between two events, a CS and a US, it also reflects knowledge about the timing of these events. A neural network and set of learning rules that generates appropriately timed conditioned response waveforms is presented. The model is capable of simulating some of the basic temporal properties of conditioned responses exhibited in biological systems, including (1) decreasing onset latency during acquisition training, (2) peak amplitude accurring at the temporal locus of the US, (3) inhibition of delay, and (4) trace conditioning. The model is also capable of simulating complex CR waveforms under certain conditions, and these simulations are compared with the results of behavioral experiments. The temporally adaptive responses are achieved by virtue of stimulus trace processes that are built into the network architecture.     

Double dissociation of amygdala and hippocampal contributions to trace and delay fear conditioning

A key finding in studies of the neurobiology of learning memory is that the amygdala is critically involved in Pavlovian fear conditioning. This is well established in delay-cued and contextual fear conditioning; however, surprisingly little is known of the role of the amygdala in trace conditioning. Trace fear conditioning, in which the CS and US are separated in time by a trace interval, requires the hippocampus and prefrontal cortex. It is possible that recruitment of cortical structures by trace conditioning alters the role of the amygdala compared to delay fear conditioning, where the CS and US overlap. To investigate this, we inactivated the amygdala of male C57BL/6 mice with GABA (A) agonist muscimol prior to 2-pairing trace or delay fear conditioning. Amygdala inactivation produced deficits in contextual and delay conditioning, but had no effect on trace conditioning. As controls, we demonstrate that dorsal hippocampal inactivation produced deficits in trace and contextual, but not delay fear conditioning. Further, pre- and post-training amygdala inactivation disrupted the contextual but the not cued component of trace conditioning, as did muscimol infusion prior to 1- or 4-pairing trace conditioning. These findings demonstrate that insertion of a temporal gap between the CS and US can generate amygdala-independent fear conditioning. We discuss the implications of this surprising finding for current models of the neural circuitry involved in fear conditioning.     

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.     

Some critical factors involved in formation of conditioned taste aversion to sodium chloride in rats

Some factors concerning acquisition and retention of conditionedtaste aversions (CTAs) were behaviorally examined in the rat.In the CTA paradigm, aqueous solution of 0.1 M NaCl was usedas the conditioned stimulus (CS) and an intraperitoneal (i.p.)injection of 0.15 M LiCl was employed as the unconditioned stimulus(US). In experiment 1, CTAs to 0.1 M NaCl were examined in bothforward (CS–US) and backward (US–CS) conditioningparadigms. Reliable CTAs were produced in the US–CS conditioningparadigm when the US–CS interval was less than 10 min,as well as in the CS–US conditioning paradigm. In experiment2, strong CTAs to 0.1 M NaCl were established when water-deprivedrats made at least 500 continuous licks, corresponding to 2.5ml intake and 2 min of drinking time. In experiment 3, effectsof gustatory deafferentation on CTA formation were studied.Only the chorda tympani played an important role in acquisitionand retention of CTAs to NaCl solutions. These results ipHimMthat strong CTAs can be acquired to 0.1 M NaCl, if its tasteinformation which is conveyed via the chorda tympani duringthe 500 continuous licks is followed by LiCl-induced sickness.     

Learning and anticipatory behaviour in a “sit-and-wait” predator: The Atlantic halibut

We studied the learning capacities and anticipatory behaviour in a “sit-and-wait” predatory fish, the Atlantic halibut, Hippoglossus hippoglossus. In Experiment 1 two groups of halibut received series of light flashes (conditioned stimulus, CS) that started before delivery of food (unconditioned stimulus, US) and persisted until after food delivery, i.e. delay conditioning. Control groups received unpaired CS and US presentations. The anticipatory behaviour of delay conditioned halibut consisted mainly of take-offs towards the surface shortly after onset of the CS. In Experiment 2 six groups of halibut were trained in three trace conditioning procedures: Two groups with 20 s, two groups with 60 s and two groups with 120 s trace interval. Learning was evident in the 20 and 60 s trace groups and in one of the 120 s trace groups. In contrast to delay conditioning the anticipatory behaviour of trace conditioned halibut was characterized by subtle movements near the tank floor with orientation towards the CS. The cautious responses of halibut after trace conditioning differed markedly from what is observed in other fish species and are suggested to reflect a “sit-and-wait” foraging strategy that requires the predator to remain undetected until the prey is within lunging range.     

A novel role for acid‐sensing ion channels in Pavlovian reward conditioning

Pavlovian fear conditioning has been shown to depend on acid‐sensing ion channel‐1A (ASIC1A); however, it is unknown whether conditioning to rewarding stimuli also depends on ASIC1A. Here, we tested the hypothesis that ASIC1A contributes to Pavlovian conditioning to a non‐drug reward. We found effects of ASIC1A disruption depended on the relationship between the conditional stimulus (CS) and the unconditional stimulus (US), which was varied between five experiments. In experiment 1, when the CS preceded the US signaling an upcoming reward, Asic1a^?/? mice exhibited a deficit in conditioning compared to Asic1a^+/+ mice. Alternatively, in experiment 2, when the CS coinitiated with the US and signaled immediate reward availability, the Asic1a^?/? mice exhibited an increase in conditioned responses compared to Asic1a^+/+ mice, which contrasted with the deficits in the first experiment. Furthermore, in experiments 3 and 4, when the CS partially overlapped in time with the US, or the CS was shortened and coinitiated with the US, the Asic1a^?/? mice did not differ from control mice. The contrasting outcomes were likely because of differences in conditioning because in experiment 5 neither the Asic1a^?/? nor Asic1a^+/+ mice acquired conditioned responses when the CS and US were explicitly unpaired. Taken together, these results suggest that the effects of ASIC1A disruption on reward conditioning depend on the temporal relationship between the CS and US. Furthermore, these results suggest that ASIC1A plays a critical, yet nuanced role in Pavlovian conditioning. More research will be needed to deconstruct the roles of ASIC1A in these fundamental forms of learning and memory.     

Some factors affecting pigeons' visual tracking behavior

A novel delayed conditional discrimination procedure was used successfully to investigate some factors affecting pigeons' tracking of visual stimuli. Trials began with the brief illumination of one of the keys (randomly selected) from the left- or right-hand column of a three by three matrix of pecking keys. Then the next key in the same row was briefly lit. Finally, the remaining key in the row was lit along with one (randomly chosen) of the remaining five keys from the left- or right-hand columns. A peck to the former but not the latter key was designated as correct and was rewarded. In Experiment 1 pigeons made correct choices on between 70 and 80 percent of trials, thereby demonstrating an ability to visually track objects. In Experiment 2 tracking accuracy was: a) reduced when either the first or second key in the sequence was omitted, b) improved when the sequence was repeated three times, c) reduced when duration of key illumination was reduced, and d) reduced by delays imposed between keys early but not late in the sequence. It was also found that tracking of vertical and horizontal sequences was approximately equal.