Context blocking in rat autoshaping: Sign-tracking versus goal-tracking

Prior experience of unsignaled food can interfere with subsequent acquisition by birds of autoshaped key-pecking at a signal light. This has been understood to indicate that unsignaled food results in context conditioning, which blocks subsequent learning about the keylight-food relationship. In the present experiment with rats lever insertion as the conditioned stimulus (CS) preceded sucrose delivery as the unconditioned stimulus (US). Half the rats initially received unsignaled USs in the conditioning context, while the remainder did not. Both lever-presses (sign-tracking) and magazine-entries (goal-tracking) were recorded. Under immediate reinforcement conditions, prior unsignaled US interfered with sign-tracking, but had no effect on goal-tracking. In two further groups, a trace condition prevented development of sign-tracking. In this case, prior context conditioning interfered with goal-tracking. These results suggest that interference with sign-tracking may reflect response competition, while interference with goal-tracking under trace conditions may reflect failure to acquire a CS-US association.     

Learning in cod (Gadus morhua): long trace interval retention

Basic knowledge about learning capacities and awareness in fish is lacking. In this study we investigated which temporal gaps Atlantic cod could tolerate between two associated events, using an appetitive trace-conditioning paradigm with blinking light as conditioned stimulus (CS) and dry fish food as unconditioned stimulus (US). CS–US presentations were either temporally overlapping (delay conditioning, CS duration 24 s, interstimulus interval 12 s) or separated by 20, 60, or 120 s (trace conditioning, CS duration 12 s) or 2 h (control, CS duration 12 s). The percentage of fish in the feeding area increased strongly during CS presentation in all delay, 20 s, and 60 s trace groups and in one out of two 120 s trace groups, but not in the control groups. In the 20 and 60 s trace procedures, the fish crowded together in the small feeding area during the trace interval, showing strong anticipatory behaviour. In all the conditioned groups, the fish responded to the CS within eight trials, demonstrating rapid learning. At 88 and 70 days after the end of the conditioning experiments, the delay and 20 s trace groups, respectively, were presented the CS six times at 2-h intervals without reward. All groups responded to the light signal, demonstrating memory retention after at least 3 months. This study demonstrates that Atlantic cod has an impressively good ability to associate two time-separated events and long time retention of learnt associations.     

吗啡对不同距离条件下大鼠信号追踪和目标追踪的影响

条件刺激短暂呈现并消失后, 奖赏立即呈现, 多次匹配后诱导出动物对条件刺激(信号追踪)或奖赏呈现装置如食盒(目标追踪)的接近。条件刺激与食盒间的距离是影响信号/目标追踪反应和损害联结学习的重要变量, 成瘾药物能够增加奖赏的诱因动机, 进而增加个体的奖赏寻求行为。距离能否通过损害联结学习而减弱成瘾药物的动机放大作用尚未见到报道。本实验采用autoshaping模型, 考察8、30和60 cm距离条件下吗啡处理对大鼠信号追踪和目标追踪的影响。结果发现：(1)信号追踪随距离增加而减少, 目标追踪对距离不敏感。(2)急性吗啡处理减少8、30和60 cm条件下信号追踪而增加8和60 cm条件下目标追踪, 慢性吗啡处理在8和30 cm条件下减少信号追踪增加目标追踪; 消退检测中, 吗啡前暴露减少8和60 cm条件下信号追踪而增加60 cm条件下目标追踪。(3)辨别反转学习中, 吗啡前暴露使30和60 cm条件下的大鼠偏爱旧信号、辨别力受损, 减少8、30和60 cm条件下大鼠对新信号的接触。这些结果提示, 距离较少影响吗啡的信号追踪抑制作用和目标追踪增强效应, 而易化吗啡前暴露对反转学习的损害。说明距离是易化成瘾药物对联结学习不利影响而非反转其动机放大作用的重要因素。     

动物信号追踪和目标追踪行为及其神经机制

信号追踪和目标追踪的实质是条件刺激和非条件刺激结合诱导的条件性接近反应.条件刺激的预测作用和诱因作用是信号追踪和目标追踪的重要机制;伏隔核、中央杏仁核和前扣带回在信号追踪和目标追踪过程中具有重要作用;然而,大脑皮层和海马损伤对两者影响较小.DA功能降低可损害信号追踪获得和表达;而脑内DA含量增加可提高目标追踪.未来的研究中,应该规范条件刺激和非条件刺激的类型和设置方法,针对不同的研究目的个别地或同时地测量信号追踪和目标追踪.     

Goal-tracking behavior in the pond snail, Lymnaea stagnalis

The occurrence of goal-tracking, an unconditioned stimulus (US)-directed autoshaping behavior, was studied in open-field tests with control and classically conditioned pond snails, Lymnaea stagnalis. In an appetitive classical conditioning paradigm with a tactile stimulus as conditioned stimulus (CS) and a localized food stimulus as US a conditioned feeding response built up in the experimental but not in the control animals. In the post-training open-field tests the experimental group alone showed an enhanced attraction toward the source of water current in the environment which previously signalled the arrival of the US but did not act as CS in the classical conditioning procedure. We suggest that this stimulus-directed goal-tracking behavior in Lymnaea is the result of a classical-operant interaction, described so far only in vertebrate animals, and that neurophysiological analysis of this behavior is possible in this snail.     

Extinction of goal tracking also eliminates the conditioned reinforcing effects of an appetitive conditioned stimulus

Previous studies have suggested that the effects of extinction are response-specific. The present study investigated whether an extinction treatment that eliminated goal tracking elicited by an appetitive conditioned stimulus (CS) would also eliminate the conditioned reinforcing effects of that CS. Rats were first trained on a goal-tracking procedure in which an auditory CS was paired with a food unconditioned stimulus. Animals learned to approach the location where the food was delivered. In a subsequent phase, rats in one group received extinction training that eliminated the goal-tracking elicited by the CS. Rats in the other group did not experience extinction of the food-paired CS. Then, both groups received a test for conditioned reinforcement in which leverpresses resulted in the brief presentation of the stimulus previously paired with food. This stimulus did not act as a conditioned reinforcer in the group that had been subjected to extinction training, but did serve as a conditioned reinforcer in the group that did not experience extinction. These results indicate that the effects of extinction generalize from the approach-eliciting to the conditioned reinforcing effects of an appetitive CS.     

Learning and memory in the Port Jackson shark,Heterodontus portusjacksoni

Basic understanding of the fundamental principles and mechanisms involved in learning is lacking for elasmobranch fishes. Our aim in this study was to experimentally investigate the learning and memory capacity of juvenile Port Jackson sharks, Heterodontus portusjacksoni. Sharks (N = 30) were conditioned over a 19-day period to associate an underwater LED light or stream of air-bubbles [conditioned stimulus (CS)] with a food reward [unconditioned stimulus (US)], using three procedures (delay, trace and control). During experiments, the CS signalled at a random time between 180 and 300 s for 30 s (six times per day). For the delay the US overlapped in time with the CS, for the trace the US delivered 10 s after the CS and for our control the US was delivered at random time between 180 and 300 s after the CS. H. portusjacksoni sharks trained in all procedures improved consistently in their time to obtain food, indicative of Pavlovian learning. Importantly, the number of sharks in the feeding area 5 s prior to CS onset did not change over time for any procedures. However, significantly more sharks were present 5 s after CS onset for delay for both air-bubble and light CS. Sharks trained in the delay and trace procedures using air-bubbles as the CS also displayed significantly more anticipatory behaviours, such as turning towards the CS and biting. Sharks trained with the light CS did not exhibit such behaviours; however, trace procedural sharks did show a significant improvement in moving towards the CS at its onset. At 20 and 40 days after the end of the conditioning experiments, some sharks were presented the CS without reward. Two sharks trained in the delay procedure using air-bubbles as the CS exhibited biting behaviours: one at 20 and the other at 40 days. This study demonstrates that H. portusjacksoni have the capacity to learn a classical conditioning procedure relatively quickly (30 trials during 5 days) and associate two time-separated events and retention of learnt associations for at least 24 h and possibly up to 40 days.     

Trace classical conditioning in rainbow trout (Oncorhynchus mykiss): what do they learn?

There are two main memory systems: declarative and procedural memory. Knowledge of these two systems in fish is scarce, and controlled laboratory studies are needed. Trace classical conditioning is an experimentally tractable model of declarative memory. We tested whether rainbow trout (Oncorhynchus mykiss) can learn by trace conditioning and form stimulus–stimulus, as opposed to stimulus–response, associations. We predicted that rainbow trout trained by trace conditioning would show appetitive behaviour (conditioned response; CR) towards the conditioned stimulus (CS; light), and that the CR would be sensitive to devaluation of the unconditioned stimulus (US; food). The learning group (L, N = 14) was trained on a CS + US contingency schedule with a trace interval of 3.4 s. The control group (CtrL, N = 4) was kept on a completely random schedule. The fish that learnt were further trained as either an experimental (L, N = 6) or a memory control (CtrM, N = 3) group. The L group had the US devalued. The CtrM group received only food. No fish in the CtrL group, but nine fish from the L group conditioned to the light. When tested, five L fish changed their CRs after US devaluation, indicating learning by stimulus–stimulus association of the light with the food. CtrM fish retained their original CRs. To the best of our knowledge, this experiment is the first to show that rainbow trout can learn by trace classical conditioning. The results indicate that the fish learnt by ‘facts-learning’ rather than by reflex acquisition in this study.     

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.     

Undernutrition during the brain growth period of the rat significantly delays the development of processes mediating Pavlovian trace conditioning

Pavlovian trace conditioning procedures allow one to assess the ability of animals to associate events that are temporally separated because the conditioned stimulus terminates prior to the occurrence of the unconditioned stimulus. We report that undernutrition during Postnatal Days 2-18 significantly delays the development of trace conditioning to a visual stimulus. Previously undernourished 20-day-old rats conditioned when no temporal interval separated the termination of the CS and US onset (0-s trace interval). However, it was not until the undernourished pups were 30 days old that they conditioned when the trace interval was 10 or 30 s. In contrast, control pups only 20 days old were able to condition when a 10-s trace interval separated the CS and US events, and 25-day-old control pups conditioned when the interval was either 10 or 30 s. These results suggest that undernutrition delays the development of processes that enable the rat to sustain a representation of a visual CS during the trace interval.     

The effects of relative intensity of cue and marker on marked trace conditioning in pigeons

Pigeons were trained on trace conditioning procedures (autoshaping) in which a keylight conditioned stimulus (CS) was presented for 5 sec and followed after a 10-sec temporal gap by food. In Experiment 1, acquisition of conditioned responding to the CS was facilitated when it was immediately followed by a brief stimulus, but only when the brief stimulus was of greater intensity than the trace CS. In Experiment 2, this facilitation effect was found when a more intense brief stimulus followed the trace CS immediately, but not when it was delayed. In both experiments, responding to the target CS was compared within-subjects to that to a control CS, which eliminated factors such as second-order conditioning as an explanation for the facilitation effects. Together, the results of Experiments 1 and 2 suggest that a brief stimulus may mark immediately preceding events in memory and thus facilitate their association with delayed reinforcement only if the brief stimulus is relatively more intense, and thus more salient, than the target events. In Experiment 3, we found substantial generalization of this facilitation effect from the marked CS to the control CS and conclude that the results of Experiments 1 and 2 may underestimate the magnitude of these marking effects.     

The Topography of Sexually Conditioned Behaviour: Effects of a Trace Interval

In a trace conditioning procedure, subjects were presented with a 30-sec conditioned stimulus (CS) followed by a 30-sec trace interval. Delayed conditioning consisted of a 60-sec CS presentation followed by an unconditioned stimulus (US). Although conditioning developed with both procedures, the topography of the conditioned response differed. Sexual conditioned approach was evident in all of the subjects during the presentation of the CS. Traceconditioned subjects moved away from the area where the CS had been presented during the trace interval but remained closer to the CS location than did an unpaired control. This reduction in the spatial specificity of the conditioned response was interpreted from a behaviour systems perspective. The trace interval presumably increased the perceived separation between the CS and the US and therefore elicited conditioned behaviour less specifically directed towards the CS.     

Timed excitatory conditioning under zero and negative contingencies

Rats (rattus norvegicus) anticipated the arrival of a food pellet unconditioned stimulus (US) even when the conditioned stimulus (CS) signaled no overall change or a substantial decrease in the overall rate of US occurrence. Pellet USs were scheduled probabilistically in the intertrial interval at either an equivalent rate (Experiment 1) or a four times higher rate (Experiments 2 and 3) than in the CS, which included one fixed-time target US. Conditioning has been said to involve learning "whether" (contingency) the CS signals a change in the US, and if so, "when" (contiguity) the US is scheduled to arrive. Our results suggest that "when" trumps "whether," challenging the received view that a positive CS-US contingency is necessary for successful conditioning.     

When congruence breeds preference: the influence of selective attention processes on evaluative conditioning

We investigated in two experiments whether selective attention processes modulate evaluative conditioning (EC). Based on the fact that the typical stimuli in an EC paradigm involve an affect-laden unconditioned stimulus (US) and a neutral conditioned stimulus (CS), we started from the assumption that learning might depend in part upon selective attention to the US. Attention to the US was manipulated by including a variant of the Eriksen flanker task in the EC paradigm. Similarly to the original Flanker paradigm, we implemented a target-distracter logic by introducing the CS as the task-relevant stimulus (i.e. the target) to which the participants had to respond and the US as a task-irrelevant distracter. Experiment 1 showed that CS–US congruence modulated EC if the CS had to be selected against the US. Specifically, EC was more pronounced for congruent CS–US pairs as compared to incongruent CS–US pairs. Experiment 2 disentangled CS–US congruence and CS–US compatibility and suggested that it is indeed CS–US stimulus congruence rather than CS–US response compatibility that modulates EC.     

Total sleep deprivation impairs the encoding of trace-conditioned memory in the rat

Sleep may help consolidate the information of certain memories, though its benefits in the consolidation of trace-conditioned memory still remain elusive. We investigated the effect of sleep deprivation on trace learning in male wistar rats. Rats were trained for trace conditioning and the number of head entries into liquid dispenser was accounted as an outcome measure of trace-learning. For training and testing, 75 presentations of conditioned stimulus (CS) (light) and unconditioned stimulus (US) (juice) were offered in five sessions (15 presentations/session; with 5 min inter-session gap). The duration of CS and US stimuli were 15 and 20s respectively, with 5s trace delay between stimuli and 20s condition delay between each presentation. The animals were divided randomly into three groups soon after training, sleep deprived (SD) (n=8), non-SD (NSD) (n=8) and stress control (n=5) groups. The animals of NSD and control groups were left undisturbed, while SD animals were sleep deprived for 6h after training. The learning of trace-conditioned task was examined on following days. We observed that SD rats poked approximately 63% less than NSD and control groups (p<0.001) to obtain juice on testing day. Also, the NSD rats exhibited significant positive correlation in number of head entries during the training and testing days; while the SD rats showed no significant correlation. The results demonstrate that SD animals had difficulties to associate CS with US and suggest that sleep deprivation soon after training impairs the encoding of trace memory.     

On two types of conditional reflex: General laws of association

Both types of conditioning are based on the general laws of associations-connections between the centers involved. Whereas the experimental procedures of classical conditioning expose mainly the conditioned stimulus (CS)-unconditioned stimulus (US) connection, those of instrumental conditioning expose the conditioned stimulus (CS)-response (R) connection. Thus, the main differences between the two types of conditioning are those associated with the different centers involved in each, not the associative-connective laws themselves.     

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.     

Trace fear conditioning is reduced in the aging rat

Auditory trace fear conditioning is a hippocampus-dependent learning task that requires animals to associate an auditory conditioned stimulus (CS) and a fear-producing shock-unconditioned stimulus (US) that are separated by an empty 20-s trace interval. Previous studies have shown that aging impairs learning performance on hippocampus-dependent tasks. This study measured heart rate (HR) and freezing fear responses to determine if aging impairs hippocampus-dependent auditory trace fear conditioning in freely moving rats. Aging and Young rats received one long-trace fear conditioning session (10 trials). Each trial consisted of a tone-CS (5 s) and a shock-US separated by an empty 20-s trace interval. The next day rats received CS-alone retention trials. Young rats showed significantly larger HR and freezing responses on the initial CS-alone retention trials compared to the Aging rats. A control group of aging rats received fear conditioning trials with a short 1-s trace interval separating the CS and US. The Aging Short-Trace Group showed HR and freezing responses on the initial CS alone retention trials that were similar to the Young Long-Trace Group, but greater than the Aging Long-Trace Group. A second aging control group received unpaired CSs and USs, and showed no HR or freezing responses on CS-alone retention trials. These data show that HR and freezing are effective measures for detecting aging-related deficits in trace fear conditioning.     

Lesions of rat infralimbic cortex enhance recovery and reinstatement of an appetitive Pavlovian response

The prefrontal cortex (PFC) has a well-established role in the inhibition of inappropriate responding, and evidence suggests that the infralimbic (IL) region of the rat medial PFC (MPFC) may be involved in some aspects of extinction of conditioned fear. MPFC lesions including, but not those sparing the IL cortex increase spontaneous recovery of extinguished conditioned fear when tested 24 h after an initial extinction session. The current experiment extended these findings by use of appetitive rather than aversive conditioning. Ten IL-lesioned and 11 sham-operated rats were trained on a Pavlovian task in which a conditioned stimulus (CS) was followed by food pellets (the unconditioned stimulus or US). IL lesions had no effect on extinction of the conditioned response (CR, magazine entries) during the first extinction session. However, the level of spontaneous recovery between the first extinction session and a second, 24 h later, was increased in IL-lesioned rats relative to sham animals. In contrast, evidence of savings measured between the extinction sessions did not differ between groups. Furthermore, reinstatement of the CR following unsignaled delivery of the US was also increased in IL-lesioned rats.