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Recent scientific evidence for fish sentience has stressed the need for novel sentience-based detection tools of fish welfare impairment in commercial farms. In order to mimic a well-characterised stress situation, rainbow trout (Oncorhynchus mykiss) were exposed to poor water quality (hypoxia combined with high ammonia level) for three weeks (stressed group, S) and compared to a non-stressed control group (NS). After a return to water quality standard, emotional responses were assessed in fish subjected to two potentially threatening situations: (i) social isolation in a novel environment and (ii) human presence. In addition, we used an appetitive-conditioning paradigm to determine whether previous chronic deterioration of water quality disturbs cognitive abilities in fish. Spontaneous behaviour in the tanks was also recorded during the environmental challenge as a reference for fish activity. We observed that in S fish, plasma cortisol levels were increased before and after social isolation in a novel environment compared to the plasma cortisol levels in the NS group, despite the absence of a behavioural difference between the two groups. Under deteriorated water quality, fish locomotor activity was globally reduced and this reduction was correlated to increased shoaling behaviour. Farmers can use these first behavioural modifications as a sentinel detector for fish welfare impairment. More importantly, we demonstrated that reactivity to a human presence in a home-environment and food-anticipatory behaviour were both inhibited in the S group. We consider that these two sentience-based tests are highly relevant for fish welfare assessment at the group level and are easy to use in the aquaculture industry.

Although post-traumatic stress disorder (PTSD) and addiction are very different disorders, both are characterized by hyperreactivity to trauma- or drug-related cues, respectively. We investigated whether an appetitive conditioning task, Pavlovian conditioned approach, which predicts vulnerability to reinstatement of cocaine-seeking, also predicts fear incubation, which may be a marker for vulnerability to PTSD. We classified rats based on whether they learned to approach and interact with a food predictive cue (sign-trackers), or, whether upon cue presentation they went to the location of impending food delivery (goal-trackers). Rats were then exposed to extensive Pavlovian tone-shock pairings, which causes the fear response to increase or “incubate” over time. We found that the fear incubation effect was only present in sign-trackers. The behavior of goal-trackers was more consistent with a normal fear response – it was most robust immediately after training and decayed slowly over time. Sign-trackers also had lower levels of brain-derived neurotrophic factor (BDNF) protein in the prefrontal cortex than goal-trackers. These results indicate that, while many factors likely contribute to the disproportionate co-occurrence of PTSD and substance abuse, one such factor may be a core psychological trait that biases some individuals to attribute excessive motivational significance to predictive cues, regardless of the emotional valence of those cues. High levels of BDNF in the prefrontal cortex may be protective against developing excessive emotional and motivational responses to salient cues.

The dorsomedial striatum (DMS) is an important sensorimotor region mediating the acquisition of goal-directed instrumental reward learning and behavioral flexibility. However, whether the DMS also regulates Pavlovian cue-food learning is less clear. The current study used excitotoxic lesions to determine whether the DMS is critical in Pavlovian appetitive learning and behavior, using discriminative conditioning and reversal paradigms. The results showed that DMS lesions transiently retarded cue-food learning and subsequent reversal of this learning. Rats with DMS lesions selectively attenuated responding to a food cue but not a control cue, early in training, suggesting the DMS is involved when initial associations are formed. Similarly, initial reversal learning was attenuated in rats with DMS lesions, which suggests impaired flexibility to adjust behavior when the cue meaning is reversed. We also examined the effect of DMS lesions on food intake during tests with access to a highly palatable food along with standard chow diet. Rats with DMS lesions showed an altered pattern of intake, with an initial reduction in high-fat diet followed by an increase in chow consumption. These results demonstrate that the DMS has a role in mediating cue-food learning and its subsequent reversal, as well as changes in food intake when a choice is provided. Together, these results demonstrate the DMS is involved in reward associative learning and reward consumption, when behavioral flexibility is needed to adjust responding or consumption to match the current value. (PsycINFO Database Record

Overweight and obese individuals show increased psychological and physiological reactivity to food cues and many of them have difficulties in achieving long-term weight loss. The current study tests whether abnormalities in the learning and extinction of appetitive responses to food cues might be responsible for this. Overweight/obese and healthy weight women completed a differential appetitive conditioning task using food as rewards, while eating expectancies, eating desires, conditioned stimulus evaluations, salivation, and electrodermal responses were assessed during an acquisition and extinction phase. Results suggested reduced discriminative conditioning in the overweight/obese group, as reflected by a worse acquisition of differential eating desires and no successful acquisition of differential evaluative responses. Some evidence was also found for impaired contingency learning in overweight and obese individuals. No group differences in conditioned salivation and skin conductance responses were found and no compelling evidence for differences in extinction was found as well. In sum, the current findings indicate that overweight and obesity may be characterized by reduced appetitive conditioning. It is suggested that this could be causally related to overeating via stronger context conditioning or a tendency towards overgeneralization in overweight and obese individuals.

Three experiments assessed how appetitive conditioning in rats changes over the duration of a trace conditioned stimulus (CS) when unsignaled unconditioned stimuli (USs) are introduced into the intertrial interval. In Experiment 1, a target US occurred at a fixed time either shortly before (embedded), shortly after (trace), or at the same time (delay) as the offset of a 120-s CS. During the CS, responding was most suppressed by intertrial USs in the trace group, less so in the delay group, and least in the embedded group. Unreinforced probe trials revealed a bell-shaped curve centered on the normal US arrival time during the trace interval, suggesting that temporally specific learning occurred both with and without intertrial USs. Experiments 2a and 2b confirmed that the bulk of the trace CS became inhibitory when intertrial USs were scheduled, as measured by summation and retardation tests, even though CS offset evoked a temporally precise conditioned response. Thus, an inhibitory CS may give rise to new stimuli specifically linked to its termination, which are excitatory. A modification to the microstimulus temporal difference model is offered to account for the data.

This study examines the role of stimulus duration in learning and memory formation of honeybees (Apis mellifera). In classical appetitive conditioning honeybees learn the association between an initially neutral, conditioned stimulus (CS) and the occurrence of a meaningful stimulus, the unconditioned stimulus (US). Thereby the CS becomes a predictor for the US eliciting a conditioned response (CR). Here we study the role of US duration in classical conditioning by examining honeybees conditioned with different US durations. We quantify the CR during acquisition, memory retention, and extinction of the early long-term memory (eLTM), and examine the molecular mechanisms of eLTM by interfering with protein synthesis. We find that the US duration affects neither the probability nor the strength of the CR during acquisition, eLTM retention, and extinction 24 h after conditioning. However, we find that the resistance to extinction 24 h after conditioning is susceptible to protein synthesis inhibition depending on the US duration. We conclude that the US duration does not affect the predictability of the US but modulates the protein synthesis underlying the eLTM's strength. Thus, the US duration differentially impacts learning, eLTM strength, and its underlying protein synthesis.

The majority of experiments exploring context-dependent extinction learning employ Pavlovian fear conditioning in rodents. Since mechanisms of appetitive and aversive learning are known to differ at the neuronal level, we sought to investigate extinction learning in an appetitive setting. Working with pigeons, we established a within-subject ABA renewal paradigm based on Rescorla (Q J Exp Psychol 61:1793) and combined it with pharmacological interventions during extinction. From the fear conditioning literature, it is known that both prefrontal cortex and the hippocampus are core structures for context-specific extinction learning. Accordingly, we transiently inactivated the nidopallium caudolaterale (NCL, a functional analogue of mammalian prefrontal cortex) and the hippocampus in separate experiments by intracranial infusion of the sodium-channel blocker tetrodotoxin immediately before extinction training. We find that TTX in both structures non-specifically suppresses conditioned responding, as revealed by a reduction of response rate to both the extinguished conditioned stimulus and a control stimulus which remained reinforced throughout the experiment. Furthermore, TTX during extinction training impaired later extinction retrieval assessed under drug-free conditions. This was true when responding to the extinguished stimulus was assessed in the context of extinction but not when tested in the context of acquisition, although both contexts were matched with respect to their history of conditioning. These results indicate that both NCL and hippocampus are involved in extinction learning under appetitive conditions or, more specifically, in the consolidation of extinction memory, and that their contribution to extinction is context-specific.

Summary Accurately predicting an outcome requires that animals learn supporting and conflicting evidence from sequential experience. In mammals and invertebrates, learned fear responses can be suppressed by experiencing predictive cues without punishment, a process called memory extinction. Here, we show that extinction of aversive memories in Drosophila requires specific dopaminergic neurons, which indicate that omission of punishment is remembered as a positive experience. Functional imaging revealed co-existence of intracellular calcium traces in different places in the mushroom body output neuron network for both the original aversive memory and a new appetitive extinction memory. Light and ultrastructural anatomy are consistent with parallel competing memories being combined within mushroom body output neurons that direct avoidance. Indeed, extinction-evoked plasticity in a pair of these neurons neutralizes the potentiated odor response imposed in the network by aversive learning. Therefore, flies track the accuracy of learned expectations by accumulating and integrating memories of conflicting events., Graphical Abstract, Highlights • Omission of expected punishment extinguishes learned avoidance behavior • Lack of punishment is learned as a positive experience • The original aversive and the new appetitive memory co-exist in different places • Opposing memories are integrated within specific output neurons to steer behavior, The omission of punishment is remembered as a rewarding experience, and this positive memory then competes against prior aversive memory to mediate the extinction of avoidance behavior.

Appetitive conditioning is considered a central mechanism for the vulnerability to psychiatric disorders. However, the investigation of individual differences that are related to altered appetitive learning has been almost neglected so far. The aim of this study was to investigate the link between neuroticism and appetitive conditioning processes. 79 subjects participated in a differential conditioning procedure in which a conditioned stimulus (CS+) was paired with a reward (money) after a fast behavioral response, while a second conditioned stimulus (CS−) was never followed by a reward, irrespective of the behavioral response. As a main result, neuroticism correlated negatively with the underlying neural processes of appetitive conditioning in females, but not in males. In detail, higher levels of neuroticism were associated with decreased neural responses in the left (p = .001) and right amygdala (p = .011), left (p = .063) and right (p = .019) nucleus accumbens, and left (p = .002) and right (p = .021) orbitofrontal cortex (all results are family-wise-error-corrected). The present results support previous findings, which also showed an inverse sex-specific effect in the context of neuroticism and emotional processing in females. In addition, the findings suggest that neuroticism is not solely linked to increased amygdala sensitivity during the processing of negative stimuli but also to decreased neural responses when processing rewarding stimuli. Possible explanations for the sex differences and implications are discussed.

An extinction cue (EC) is a discrete stimulus that is presented during Pavlovian extinction, contingent and with close contiguity to the conditioned stimulus (CS) under extinction treatment. When this EC is presented during a recovery test (e.g., renewal, spontaneous recovery), it typically prevents response recovery. At least two associative mechanisms have been proposed to explain this effect: an EC might become a conditioned inhibitor, or it might become a negative occasion setter. Three experiments, using rats as subjects, assessed whether an EC prevented renewal, and evaluated with summation and retardation tests as to whether it acquired conditioned inhibition. Experiment 1 was conducted in a fear conditioning preparation, and experiments 2 and 3 in an appetitive conditioning paradigm. The results of the three experiments showed that an EC did not attenuate renewal compared to a novel cue, and subsequent inhibition tests also showed no difference between the EC and a novel stimulus. These results suggest that the effect might be more difficult to detect than expected, and are discussed within the framework of previous studies.

Cues that predict the availability of food rewards influence motivational states and elicit food-seeking behaviors. If a cue no longer predicts food availability, then animals may adapt accordingly by inhibiting food-seeking responses. Sparsely activated sets of neurons, coined “neuronal ensembles,” have been shown to encode the strength of reward–cue associations. Although alterations in intrinsic excitability have been shown to underlie many learning and memory processes, little is known about these properties specifically on cue-activated neuronal ensembles. We examined the activation patterns of cue-activated orbitofrontal cortex (OFC) and nucleus accumbens (NAc) shell ensembles using wild-type andFos-GFPmice, which express green fluorescent protein (GFP) in activated neurons, after appetitive conditioning with sucrose and extinction learning. We also investigated the neuronal excitability of recently activated, GFP+ neurons in these brain areas using whole-cell electrophysiology in brain slices. Exposure to a sucrose cue elicited activation of neurons in both the NAc shell and OFC. In the NAc shell, but not the OFC, these activated GFP+ neurons were more excitable than surrounding GFP− neurons. After extinction, the number of neurons activated in both areas was reduced and activated ensembles in neither area exhibited altered excitability. These data suggest that learning-induced alterations in the intrinsic excitability of neuronal ensembles is regulated dynamically across different brain areas. Furthermore, we show that changes in associative strength modulate the excitability profile of activated ensembles in the NAc shell.SIGNIFICANCE STATEMENTSparsely distributed sets of neurons called “neuronal ensembles” encode learned associations about food and cues predictive of its availability. Widespread changes in neuronal excitability have been observed in limbic brain areas after associative learning, but little is known about the excitability changes that occur specifically on neuronal ensembles that encode appetitive associations. Here, we reveal that sucrose cue exposure recruited a more excitable ensemble in the nucleus accumbens, but not orbitofrontal cortex, compared with their surrounding neurons. This excitability difference was not observed when the cue's salience was diminished after extinction learning. These novel data provide evidence that the intrinsic excitability of appetitive memory-encoding ensembles is regulated differentially across brain areas and adapts dynamically to changes in associative strength.

An automated device and a procedure for the operant conditioning individual zebrafish were developed. The key feature of this procedure was the construction of a simple, inexpensive feeder that can deliver extremely small amounts of food, thus preventing rapid satiation. This allows the experimenter to run multiple trails in a single test session and multiple sessions in one day. In addition, small response keys made from acryl rods and fiber sensors were developed that were sufficiently sensitive to detect fish contact. To illustrate the efficiency and utility of the device for traditional learning paradigms, we trained zebrafish in a fixed ratio schedule where subjects were reinforced with food after 10 responses. Zebrafish reliably responded on the response key for sessions that lasted as long 80-reinforcements. They also showed the traditional "break and run" response pattern that has been found in many species. These results show that this system will be valuable for behavioral studies with zebrafish, especially for experiments that need many repeated trials using food reinforcer in a session. The present system can be used for sensory and learning investigations, as well applications in behavioral pharmacology, behavioral genetics, and toxicology where the zebrafish is becoming the vertebrate model of choice.

Emotionally arousing events are typically better remembered than mundane ones, in part because emotionally relevant aspects of our environment are prioritized in attention. Such biased attentional tuning is itself the result of associative processes through which we learn affective and motivational relevance of cues. We propose that the locus coeruleus-noradrenaline (LC-NA) system plays an important role in the genesis of attentional biases through associative learning processes as well as their maintenance. We further propose that individual differences in and disruptions of the LC-NA system underlie the development of maladaptive biases linked to psychopathology. We provide support for the proposed role of the LC-NA system by first reviewing work on attentional biases in development and its link to psychopathology in relation to alterations and individual differences in NA availability. We focus on pharmacological manipulations to demonstrate the effect of a disrupted system as well as theADRA2bpolymorphism as a tool to investigate naturally occurring differences in NA availability. We next review associative learning processes that—modulated by the LC-NA system—result in such implicit attentional biases. Further, we demonstrate how NA may influence aversive and appetitive conditioning linked to anxiety disorders as well as addiction and depression.

Intertidal fishes have elaborated spatial cognitive abilities. In this study, we developed an appetitive conditioning paradigm for an intertidal fish species (the chameleon goby; Tridentiger trigonocephalus) that involves spatial components and ethologically relevant cue stimuli. The gobies rapidly acquired the conditioned anticipatory behaviour after only a few trials of paired presentations of virtual tidal changes and food rewards (which were only available in specific locations during a simulated high tide). The conditioned responses were retained after exposure to a 1 month period without trainings or tidal changes. The rapid acquisition and long-term retention of the conditioned responses indicates that the learning paradigm, which used a combination of water level changes and food availability in specific spatial locations, is biologically significant for this species. Taken together, these results suggest that spatial tasks combined with virtual tidal changes provide a suitable paradigm for evaluating spatial cognitive mechanisms in intertidal fishes.

Two appetitive conditioning experiments with rats investigated the mechanisms and properties of unblocking that results from the surprising omission of an expected post-trial unconditioned stimulus (US). Experiment 1 demonstrated unblocking under circumstances in which differences in the contribution of generalization decrement and within-compound associations are equated across experimental and control groups. Following Stage 1 training in which a conditioned stimulus (CS) A was followed by a US and a post-trial US, in Experiment 2 we arranged for the post-trial US to be present on some trials with AX but not others. Under these circumstances an enhancement of unblocking to X was observed, relative to a group who received standard unblocking by US omission. The implications of these results for attentional and US-processing theories of associative learning are discussed.

Computerized tasks based on conditioned place preference (CPP) methodology offer the opportunity to study learning mechanisms involved in conditioned reward in humans. In this study, we examined acquisition and extinction of a CPP for virtual environments associated with monetary reward ($). Healthy men and women (N=57) completed a computerized CPP task in which they controlled an avatar within a virtual environment. On day 1, subjects completed 6 conditioning trials in which one room was paired with high $ and another with low $. Acquisition of place conditioning was assessed by measuring the time spent in each room during an exploration test of the virtual environments and using self-reported ratings of room liking and preference. Twenty-four hours later, retention and extinction of CPP were assessed during 4 successive exploration tests of the virtual environments. Participants exhibited a place preference for (spent significantly more time in) the virtual room paired with high $ over the one paired with low $ (p=0.015). They also reported that they preferred the high $ room (p

Questions regarding the nature of nonhuman cognition continue to be of great interest within cognitive science and biology. However, progress in characterizing the relative contribution of "simple" associative and more "complex" reasoning mechanisms has been painfully slow-something that the tendency for researchers from different intellectual traditions to work separately has only exacerbated. This article reexamines evidence that rats respond differently to the nonpresentation of an event than they do if the physical location of that event is covered. One class of explanation for the sensitivity to different types of event absence is that rats' representations go beyond their immediate sensory experience and that covering creates uncertainty regarding the status of an event (thus impacting on the underlying causal model of the relationship between events). A second class of explanation, which includes associative mechanisms, assumes that rats represent only their direct sensory experience and that particular features of the covering procedures provide incidental cues that elicit the observed behaviors. We outline a set of consensus predictions from these two classes of explanation focusing on the potential importance of uncertainty about the presentation of an outcome. The example of covering the food-magazine during the extinction of appetitive conditioning is used as a test case for the derivation of diagnostic tests that are not biased by preconceived assumptions about the nature of animal cognition. (PsycINFO Database Record

Food cue reactivity is a strong motivation to eat, even in the absence of hunger. Therefore, food cue reactivity might sabotage healthy eating, induce weight gain and impede weight loss or weight maintenance. Food cue reactivity can be learned via Pavlovian appetitive conditioning: It is easily acquired but the extinction of appetitive responding seems to be more challenging. Several properties of extinction make it fragile: extinction does not erase the original learning and extinction is context-dependent. These properties threaten full extinction and increase the risk of full relapse. Extinction procedures are discussed to reduce or prevent the occurrence of rapid reacquisition, spontaneous recovery, renewal and reinstatement after extinction. A translation to food cue exposure treatment is made and suggestions are provided, such as conducting the exposure in relevant contexts, using occasional reinforcement and targeting expectancy violation instead of habituation. A new hypothesis proposed here is that the adding of inhibition training to strengthen inhibition skills that reduce instrumental responding, might be beneficial to improve food cue exposure effects.

We describe here an automated apparatus that permits rapid conditioning paradigms for zebrafish. Arduino microprocessors were used to control the delivery of auditory or visual stimuli to groups of adult or juvenile zebrafish in their home tanks in a conventional zebrafish facility. An automatic feeder dispensed precise amounts of food immediately after the conditioned stimuli, or at variable delays for controls. Responses were recorded using inexpensive cameras, with the video sequences analysed with ImageJ or Matlab. Fish showed significant conditioned responses in as few as 5 trials, learning that the conditioned stimulus was a predictor of food presentation at the water surface and at the end of the tank where the food was dispensed. Memories of these conditioned associations persisted for at least 2days after training when fish were tested either as groups or as individuals. Control fish, for which the auditory or visual stimuli were specifically unpaired with food, showed no comparable responses. This simple, low-cost, automated system permits scalable conditioning of zebrafish with minimal human intervention, greatly reducing both variability and labour-intensiveness. It will be useful for studies of the neural basis of learning and memory, and for high-throughput screening of compounds modifying those processes.

Human laboratory studies have shown that eating desires are easily learned through classical conditioning: after a few pairings of an initially neutral stimulus (e.g., a box) with the intake of palatable food (e.g., chocolate), the stimulus elicits increased eating expectancies and eating desires (acquisition). After repeated non-reinforced presentations of the chocolate-associated stimulus, eating expectancies and desires decrease again (extinction). It is commonly assumed that eating desires in daily life are acquired and extinguished in a similar manner, but to date, this has not been empirically tested. In two studies, we examined whether the repeated consumption of chocolate at a specific time of day elicits increased eating expectancies and eating desires over a period of 5 days (study 1) or 15 days (study 2), and relative to a time of day not paired with chocolate intake. Further, it was tested whether acquired responding diminishes again during extinction (study 1). Ecological momentary assessment was used to carry out the studies in daily life. Results showed that eating expectancies were acquired in both studies. Only in study 2, eating desires were also successfully learned. It is concluded that eating expectancies and eating desires can be conditioned to ecologically valid cues and under real-life circumstances. This highlights the importance of associative learning processes in the experience of eating desires in daily life.

Protein degradation is known to affect memory formation after extinction learning. We demonstrate here that an inhibitor of protein degradation, MG132, interferes with memory formation after extinction learning in a classical appetitive conditioning paradigm. In addition, we find an enhancement of memory formation when the same inhibitor is applied after initial learning. This result supports the idea that MG132 targets an ongoing consolidation process. Furthermore, we demonstrate that the sensitivity of memory formation after initial learning and extinction learning to MG132 depends in the same way on the number of CS-US trials and the intertrial interval applied during initial learning. This supports the idea that the learning parameters during acquisition are critical for memory formation after extinction and that protein degradation in both learning processes might be functionally linked.

SummaryIt is broadly accepted that long-term memory (LTM) is formed sequentially after learning and short-term memory (STM) formation, but the nature of the relationship between early and late memory traces remains heavily debated [1–5]. To shed light on this issue, we used an olfactory appetitive conditioning in Drosophila, wherein starved flies learned to associate an odor with the presence of sugar [6]. We took advantage of the fact that both STM and LTM are generated after a unique conditioning cycle [7, 8] to demonstrate that appetitive LTM is able to form independently of STM. More specifically, we show that (1) STM retrieval involves output from γ neurons of the mushroom body (MB), i.e., the olfactory memory center [9, 10], whereas LTM retrieval involves output from αβ MB neurons; (2) STM information is not transferred from γ neurons to αβ neurons for LTM formation; and (3) the adenylyl cyclase RUT, which is thought to operate as a coincidence detector between the olfactory stimulus and the sugar stimulus [11–14], is required independently in γ neurons to form appetitive STM and in αβ neurons to form LTM. Taken together, these results demonstrate that appetitive short- and long-term memories are formed and processed in parallel.

In an experiment with rats, an appetitive conditioning method was used to investigate the generality of the hypothesis that extinction should arouse attention to contextual cues, resulting in all learning in that context becoming context specific. Rats received appetitive conditioning with a tone either while extinction of a flasher occurred (Group With Extinction) or while it did not (Group No Extinction). Half of each group was subsequently tested in extinction in the context in which training had taken place or in a different context. The results revealed a three-way interaction of extinction and context with trials, in a direction opposite to the one the hypothesis would suggest. When rats were tested in a different context, there was generally better responding in Group With Extinction than in Group No Extinction. In the same context, there was generally lower responding in Group With Extinction than in Group No Extinction. Subsequent testing showed an ABA recovery effect. Results are discussed in terms of the challenges they pose for the revised retrieval theory presented by Callejas-Aguilera and Rosas (2011).

The integrity of the rodent anterior cingulate cortex (ACC) is essential for various aspects of instrumental behavior, but it is not clear if the ACC is important for the acquisition of a simple instrumental response. Here, it was demonstrated that post-session infusions of anisomycin into the rat ACC completely prevented the acquisition of instrumental responding. The experimental use of post-session intracranial infusions of plasticity inhibitors is assumed to affect local consolidation of plasticity, but not behavioral task performance. However, in associative appetitive conditioning, post-session intracranial infusion of pharmaco-active compounds could actually interfere with subsequent task performance indirectly through retrospective effects on the valuation of ingested rewards. Thus, it was subsequently demonstrated that the intracranial infusion of anisomycin into the ACC after sucrose pellet consumption significantly reduced subsequent pellet consumption, suggesting that the infusion of anisomycin into the ACC produced conditioned taste avoidance. In the third experiment, an innovative procedure was introduced that dissociated the effects of intracranial infusions after conditioning sessions on task-learning and unconditioned stimulus valuation. With this procedure, the infusion of anisomycin into the ACC after instrumental sessions did not affect instrumental reinforcer valuation or the acquisition of instrumental responding, suggesting that plasticity in the ACC is not necessary for the acquisition of instrumental behavior.

In three experiments with rat subjects, we examined the effects of trial spacing in appetitive conditioning. Previous research in this preparation suggests that self-generated priming of the conditional stimulus (CS) and/or unconditional stimulus (US) in short-term memory is a cause of the trial-spacing effect that occurs with intertrial intervals (ITIs) of less than 240 sec. Experiment 1 nonetheless showed that a trial-spacing effect still occurs when ITIs are increased beyond 240 sec, and that the effect of ITI over 60-1,920 sec on conditioned responding is best described as a linear function. In Experiment 2, some subjects were removed from the context during the ITIs, preventing extinction of the context. Removal abolished the advantage of the long ITI, suggesting the importance of exposure to the context during the long ITI. Experiment 3 still produced a trial-spacing effect in a within-subjects design that controlled for the level of context conditioning and reinforcement rate in the absence of the CS. Overall, the results are most consistent with the idea that adding time to the ITI above 240 sec facilitates conditioning by extinguishing context-CS associations--and possibly context-US associations--that otherwise interfere with CS-US learning through retrieval-generated priming (see, e.g., Wagner, 1981).

Four experiments with rats studied the effects of switching the context after Pavlovian conditioning. In three conditioned suppression experiments, a large number of conditioning trials created "inhibition with reinforcement" (IWR), in which fear of the conditional stimulus (CS) reached a maximum and then declined despite continued CS-unconditional stimulus pairings. When IWR occurred, a context switch augmented fear of the CS; IWR and augmentation were highly correlated. Neither IWR nor augmentation resulted from inhibition of delay (IOD): In conditioned suppression, IWR and augmentation occurred without IOD (Experiment 3), and in appetitive conditioning (Experiment 4), IOD occurred without IWR or augmentation. IWR may occur in conditioned suppression because the animal adapts to fear of the CS in a context-specific manner. The authors discuss several implications.

The land slug Limax performs both aversive and appetitive olfactory learning, and we investigated neurotransmitters involved in each type of learning. Slugs were conditioned by presenting a vegetable juice (appetitive conditioning) or a mixture of vegetable juice and quinidine (aversive conditioning), and the latency to reach the juice became shorter (appetitive conditioning) or longer (aversive conditioning) after conditioning. L-NAME injected either before conditioning or testing blocked the reduction in latency in appetitive conditioning but had no significant effects in aversive conditioning. 5,7-dihydroxytryptamine had no significant effects in appetitive conditioning. These results suggest different mechanisms for appetitive and aversive learning.

Four experiments examined the effects of varying the conditioned stimulus-unconditioned stimulus (CS-US) interval (and US density) on learning in an appetitive magazine approach task with rats. Learning was assessed with conditioned response (CR) measures, as well as measures of sensory-specific stimulus-outcome associations (Pavlovian-instrumental transfer, potentiated feeding, and US devaluation). The results from these studies indicate that there exists an inverse relation between CS-US interval and magazine approach CRs, but that sensory-specific stimulus-outcome associations are established over a wide range of relatively long, but not short, CS-US intervals. These data suggest that simple CR measures provide different information about what is learned than measures of the specific stimulus-outcome association, and that time is a more critical variable for the former than latter component of learning.

Three experiments explored the utility of considering mechanisms of occasion setting for understanding patterning and biconditional discriminations - two more complex conditional discriminations in which the stimulus-outcome relations of occasion setting are embedded. In Experiment 1, rats were trained in an appetitive conditioning task with either a biconditional or a patterning discrimination using relatively brief CSs (10 s) and differential outcomes as USs. In this study, rats learned the positive patterning task before they had learned negative patterning, and the biconditional task was the most difficult. However, a detailed examination of the results suggested that rats trained in the biconditional task responded to the stimulus compounds mainly on the basis of individual stimulus-outcome associations. Different conditioned response (CR) topographies as a function of reinforcer type complicated interpretation of these results. Experiment 2 confirmed that the biconditional task, with the parameters used here, was not learned, regardless of whether training involved differential or non-differential outcomes. In Experiment 3 the CS duration was increased to 30 s and two different USs were used that each supported similar CR topographies. Under these conditions, we observed that whereas the positive patterning task was learned most rapidly, the biconditional discrimination was learned faster than the negative patterning task. Considered in relation to other findings on patterning and biconditional discriminations, the results suggest that elemental, configural, and/or modulatory occasion setting mechanisms may play different roles in these complex conditional discrimination tasks especially as a function of stimulus duration and differential outcome training.

© 2016 Cold Spring Harbor Laboratory Press. Pavlovian conditioning is the process by which we learn relationships between stimuli and thus constitutes a basic building block for how the brain constructs representations of the world. We first review the major concepts of Pavlovian conditioning and point out many of the pervasive misunderstandings about just what conditioning is. This brings us to a modern redefinition of conditioning as the process whereby experience with a conditional relationship between stimuli bestows these stimuli with the ability to promote adaptive behavior patterns that did not occur before the experience.Working from this framework, we provide an in-depth analysis of two examples, fear conditioning and food-based appetitive conditioning, which include a description of the only partiallyoverlapping neural circuitry of each. We also describe how these circuits promote the basic characteristics that define Pavlovian conditioning, such as error-correction-driven regulation of learning.

Appetitive learning has been demonstrated several times using neutral cues or contexts as a predictor of food intake and it has been shown that humans easily learn cued desires for foods. It has, however, never been studied whether internal cues are also capable of appetitive conditioning. In this study, we tested whether humans can learn cued eating desires to negative moods as conditioned stimuli (CS), thereby offering a potential explanation of emotional eating (EE). Female participants were randomly presented with 10 different stimuli eliciting either negative or neutral emotional states, with one of these states paired with eating chocolate. Expectancy to eat, desire to eat, salivation, and unpleasantness of experiencing negative emotions were assessed. After conditioning, participants were brought into a negative emotional state and were asked to choose between money and chocolate. Data showed differential conditioned responding on the expectancy and desire measures, but not on salivation. Specific conditioned effects were obtained for participants with a higher BMI (body mass index) on the choice task, and for participants high on EE on the unpleasantness ratings. These findings provide the first experimental evidence for the idea that negative emotions can act as conditioned stimuli, and might suggest that classical conditioning is involved in EE.

d-Cycloserine, a partial NMDA agonist, significantly accelerated extinction of a cocaine-induced conditioned place preference (CPP) when rats were given systemic injections immediately, but not 4h, after each extinction trial. Infusions directly into the basolateral amygdala had a similar effect. The facilitative effect of d-cycloserine on the extinction of appetitive conditioning is consistent with the idea of the formation of new learned associations during extinction.

The amygdala is a heterogeneous structure that has been implicated in a wide variety of functions, most notably in fear conditioning. From this research, an influential serial model of amygdala processes has emerged in which aversive learning is mediated by the amygdala basolateral nucleus whereas performance, in this case of various defensive reflexes, is mediated by the central nucleus. By contrast, recent evidence from appetitive conditioning studies suggests that the basolateral and central nuclei operate in parallel to mediate distinct incentive processes: the basolateral nucleus encodes emotional events with reference to their particular sensory-specific features, whereas the central nucleus encodes their more general motivational or affective significance. Given that there is little if any direct behavioral evidence for the serial model, we suggest that more attention should be given to the claims of the parallel view.

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.

Three experiments examined absolute (Experiment 1) and relative (Experiments 2a and 2b) duration effects on blocking. In Experiment 1, rats were pretrained with a short or long conditioned stimulus (CS1) followed by food, after which they were given reinforced short-short or long-long CS1-CS2 simultaneous compounds. Compared to overshadowing control groups, both pretrained groups displayed blocking, and there was no clear effect of absolute stimulus duration on the magnitude of blocking. In Experiments 2a and 2b, the rats received partially overlapping short-long CS1-CS2 compounds. In both experiments, a long CS1 blocked a short CS2, but not vice versa. This was the case when the long CS1 was nine times (Experiment 2a) or only 1.5 times (Experiment 2b) the duration of the short CS2. The pattern of results is most consistent with a real-time model of conditioning, such as the Sutton and Barto [Sutton, R.S., Barto, A.G., 1990. Time derivative models of Pavlovian reinforcement. In: Gabriel, M.R., Moore, J.W. (Eds.), Learning and Computational Neuroscience: Foundations of Adaptive Networks. MIT Press, Cambridge, MA, 497-537] temporal difference model.

This paper considers issues arising from presentations by Barry Everitt and Gorica Petrovich concerning amygdalar involvement in appetitive conditioning. Studies reported by these researchers are beginning to unravel the distribution of associative functions among amygdalar nuclei and their efferent targets. The main issue addressed here concerns how to integrate the information from studies of appetitive conditioning with conclusions from studies of other forms of associative learning, including pavlovian fear conditioning and instrumental conditioning. Most students of this issue will agree that no prima facie integration is readily apparent in current scholarship. Although we do not here provide the definitive integration, we do attempt to take some preliminary, broad-brush steps towards that goal.

This study assessed basic learning and attention abilities in Wistar-Kyoto hyperactive (WKHA) rats using appetitive conditioning preparations. Two measures of conditioned responding to a visual stimulus, orienting behavior (rearing on the hind legs), and food cup behavior (placing the head inside the recessed food cup) were measured. In Experiment 1, simple conditioning, but not extinction, was impaired in WKHA rats compared with Wistar rats. In Experiment 2, nonreinforced presentations of the visual cue preceded the conditioning sessions. WKHA rats displayed less orienting behavior than Wistar rats but comparable levels of food cup behavior. These data suggest that WKHA rats exhibit specific abnormalities in attentional processing as well as in learning stimulus-reward relationships.

Learning to associate a conditioned (CS) and unconditioned stimulus (US) results in changes in the processing of CS information. Here, we address directly the question whether chemical appetitive conditioning of Lymnaea feeding behavior involves changes in the peripheral and/or central processing of the CS by using extracellular recording techniques to monitor neuronal activity at two stages of the sensory processing pathway. Our data show that appetitive conditioning does not affect significantly the overall CS response of afferent nerves connecting chemosensory structures in the lips and tentacles to the central nervous system (CNS). In contrast, neuronal output from the cerebral ganglia, which represent the first central processing stage for chemosensory information, is enhanced significantly in response to the CS after appetitive conditioning. This demonstrates that chemical appetitive conditioning in Lymnaea affects the central, but not the peripheral processing of chemosensory information. It also identifies the cerebral ganglia of Lymnaea as an important site for neuronal plasticity and forms the basis for detailed cellular studies of neuronal plasticity.

Two appetitive conditioning experiments with rats examined reacquisition after conditioned responding was eliminated by either extinction or by a partial reinforcement procedure in which reinforced trials were occasionally presented among many nonreinforced trials. In Experiment 1, reacquisition to a conditional stimulus (CS) that had been conditioned and extinguished was more rapid than acquisition in a group that had received no prior conditioning. However, the addition of occasional reinforced trials to extinction slowed this rapid reacquisition effect. Experiment 2 replicated the result and showed that a procedure in which the CS and the unconditional stimulus (US) were unpaired in extinction interfered even further with reacquisition. The results suggest that rapid reacquisition is ordinarily produced when reinforced trials provide a contextual cue that can renew responding by signaling other acquisition trials ( Ricker & Bouton, 1996 ). The effects of partial reinforcement in extinction are surprising from several theoretical perspectives and have useful clinical implications.

Numerous environmental features have the potential to act as ‘barriers’ to fishes in the field. Passage of these ‘barriers’ depends on two main properties: willingness (behavioural) and physiological capacity. The physiological swimming capacity of fishes has been well studied. However, because most barrier research has focused on the population level effects of man – made barriers, little attention has been given to the behavioural aspects of fish passage. We used appetitive conditioning to create a simple laboratory based protocol to estimate behavioural limits to fish passage. We tested our protocol using barrier height (or passage space) as a model. Our protocol successfully identified behavioural limits in two species, juvenile rainbow trout, Oncorhynchus mykiss, and fathead minnows, Pimephales promelas. Our most interesting observation was that even a partial, submerged barrier had the potential to block fish movements. Our results suggest a potential use for conditioning techniques in assessing factors that constitute behaviour barriers to fishes. This information may help us to better predict fish movements in the field and may help us to design barriers that are more efficient at passing fishes.

Conditioning trials that are massed in time produce less conditioning than those that are spaced in time. Four experiments with rat subjects examined whether a recent conditioning trial interferes with conditioning on the next trial by temporarily "priming" information in short-term memory (e.g., Wagner, 1978, 1981). We used appetitive conditioning procedures in which priming trials preceded target trials by 60 sec. When the priming trials were nonreinforced presentations of a conditioned stimulus (CS), the CS had to be the same CS as the one on the target trial to interfere with conditioning. When priming trials were actual CS-unconditioned stimulus (US) pairings, the CS identity did not matter, the US was the event that interfered with conditioning on the next trial. Reinforced trials reduced performance in a way that did not depend on context blocking. The results suggest that CS and US priming effects do contribute to conditioning deficits observed with massed trial procedures. The results are consistent with Wagner's (1981) "sometimes opponent process," or SOP, model, although a result that is paradoxical for the model suggests that recent USs may have motivational as well as memory effects.