Stress-induced breakdown of an appetitive discrimination

Rats trained to discriminate between S^D and S^Δ for food reinforcement showed marked impairments in this discrimination when strong, unavoidable shocks occurred at the termination of a third stimulus. The predominant feature of this impairment was a supernormal rate of unreinforced (S^Δ) behavior. Shocks delivered without exteroceptive warning also led to a discriminative breakdown. The effect was a direct function of shock intensity. When behavior was strongly suppressed in the third stimulus by response-correlated shock (“punishment”), instead of unavoidable shock, breakdowns were only temporary; as soon as responding recovered from its overall suppression, discriminative performance returned to normal. The discriminative deterioration may be interpreted as an emotional by-product of frequent aversive stimulation, but accidental contingencies could also have played a role.     

Analysis of us-preexposure effects in appetitive conditioning

In two experiments, rats received preexposure to one type of food followed by autoshaping in which presentation of one lever was associated with the preexposed food, and presentation of another lever with a novel type of food pellet. In both it was found that acquisition of the leverpress response occurred more readily on the lever associated with the novel food. This example of the US (unconditioned stimulus) preexposure effect is not to be explained in terms of the development of competing responses during preexposure. Explanations in terms of blocking by contextual cues and of habituation to the US are considered.     

Manipulating affective state influences conditioned appetitive responses

Affective states influence how individuals process information and behave. Some theories predict emotional congruency effects (e.g. preferential processing of negative information in negative affective states). Emotional congruency should theoretically obstruct the learning of reward associations (appetitive learning) and their ability to guide behaviour under negative mood. Two studies tested the effects of the induction of a negative affective state on appetitive Pavlovian learning, in which neutral stimuli were associated with chocolate (Experiment 1) or alcohol (Experiment 2) rewards. In both experiments, participants showed enhanced approach tendencies towards predictors of reward after a negative relative to a positive performance feedback manipulation. This increase was related to a reduction in positive affect in Experiment 1 only. No effects of the manipulation on conditioned reward expectancies, craving, or consumption were observed. Overall, our findings support the idea of counter-regulation, rather than emotional congruency effects. Negative affective states might therefore serve as a vulnerability factor for addiction, through increasing conditioned approach tendencies.     

Aversive learning overcomes appetitive innate responding in honeybees

Despite their miniature brain, honeybees have emerged as a powerful model for the study of learning and memory. Yet, they also exhibit innate responses to biologically relevant social signals such as pheromones. Here, we asked whether the bees’ developed learning capabilities allow them to overcome hardwired appetitive responses. Can they learn that attractant pheromones, that are not normally associated with a noxious stimulation in nature, predict the punishment of an electric shock? Immobilized honeybees were trained to discriminate two odorants, one that was paired with a shock and another that had no consequences. We measured whether they learned to produce aversive sting extension responses to the punished but not the non-punished odorant. One odorant was a neutral odor without innate value while the other was either an attractive pheromone (geraniol or citral) or an attractive floral odorant (phenylacetaldehyde). In all cases, bees developed a conditioned aversive response to the punished odorant, be it pheromone or not, and efficiently retrieved this information 1 h later. No learning asymmetries between odors were found. Thus, associative aversive learning in bees is strong enough to override preprogrammed responding, thus reflecting an impressive behavioral flexibility.     

Personality and conditioning with appetitive and aversive stimuli

Two studies examining relationships of extraversion (E), neuroticism (N) and psychoticism (P) to conditioning performance are reported. In the first, 31 male volunteers developed electrodermal CRs to appetitive or aversive stimuli of either weak or strong rated intensity. Factor analysis yielded general factors of classical CR acquisition and extinction across reinforcement type. Stability and E loaded the acquisition factor, these Ss, from post-hoc analysis, revealing superior conditioning in the strong appetitive condition. In the second study, 20 of these 31 Ss participated in two series of discrimination motor reaction time trials, in which attainment of criterion RT was reinforced by appetitive slides, and slower-than-criterion responding by aversive slides. Introversion was correlated with greater response acquisition under both conditions, although post-hoc analysis suggested that improvement under positive reinforcement did not differ from simple practice. Results are congruent with a model combining reinforcer preference with response potential to describe personality-conditioning relationships.     

Effects of acetoxycycloheximide on appetitive learning and memory

The effects of direct brain infusions of acetoxycycloheximide (an inhibitor of protein synthesis; ACXH) on acquisition, storage and recall of memory for one-trial appetitive learning were examined in five experiments. ACXH was infused into the rats' hippocampi through implanted cannulas. Control subjects received an equal volume of physiological saline. ACXH was infused (a) 5 h before acquisition, (b) 5 hr before commencement of recall tests, and (c) immediately after acquisition. Each subject's general motor activity was recording during testing. The results indicate that (1) ACXH has similar effects on appetitive and avoidance learning. (2) ACXH administered immediately after acquisition, has no effect on memory. (3) At 4 hr after acquisition memory is affected by ACXH. (4) Short-term memory is unaffected by ACXH and can exist independently of long-term memory. (5) ACXH consistently reduces general motor activity.     

Counterconditioning of appetitive and defensive CRs in rabbits

Two experiments examined interactions between conditioned appetitive and defensive responses in the rabbit. In Experiment I, a conditioned jaw-movement response was established by following presentations of a clicker CS with intra-oral sucrose delivery on 50% of trials. The jaw-movement response was then maintained on this partial reinforcement schedule during a counterconditioning phase. A group which received para-orbital shock paired with the CS on non-sucrose trials showed acquisition of eyeblink responding and suppression of jaw-movement responding to the CS, in comparison to control groups which received either no shock or unpaired presentations of the CS and shock. Experiment II was identical in design to Experiment I except that the roles of the sucrose and shock reinforcers were reversed. The paired group acquired a conditioned jaw-movement response when sucrose was added in the counterconditioning phase, but in contrast to Experiment I showed a slight enhancement of the previously established eyeblink response. The asymmetry of appetitive and defensive counterconditioning was discussed in relation to opponent-process theories of motivation and reinforcement.     

One-trial appetitive conditioning in the sexual behavior system

One-trial Pavlovian conditioning has been demonstrated with aversive reinforcers such as electric shock and lithium chloride. The present experiments using male Japanese quail were conducted to determine if an appetitive unconditioned stimulus (US), the opportunity to copulate with a female quail, can also generate one-trial learning. In Experiment 1, subjects were exposed to a contextual conditioned stimulus (CS) for 35 sec and then given copulatory opportunity. In Experiment 2, male birds were given 0, 2, or 4 min of exposure to the contextual CS before presentation of a female. In both cases, control groups received comparable exposure to both the contextual CS and the sexual US, but in an unpaired fashion. Subjects were tested for sexual learning by reintroducing them to the experimental context in the presence of a test object that incorporated the taxidermically prepared head of a female quail. In both Experiments 1 and 2, subjects for whom the contextual CS and sexual US had been paired displayed significantly more approach to the test object than did unpaired subjects.     

Effects of posttraining ethanol on an appetitive task

The present study examined the effects of posttraining ethanol administration upon retention of an appetitive task using a variety of retention behaviors associated with the task. Male C57BL/6J mice were individually trained to find a cheese pellet placed in the corner of an open field. Five behavioral measures were used including locomotor activity counts, rearings, grooming episodes, approaches to the cheese pellet, and latency to consume the cheese pellet. Immediately after training, mice were injected intraperitoneally with saline or 2.0 g/kg of ethanol and then returned to their home cage in which four "intruder" mice were added for 2 h after training. On subsequent testing days (1, 6, 14, and 51 days posttraining), mice were returned to the original training environment and the five behaviors were measured. Both saline- and ethanol-treated mice habituated to the initially novel test environment at similar rates as indicated by decreased exploratory behavior (locomotor activity and rearings). In contrast, a divergence in the latency to consume the cheese pellet was observed: Saline-treated mice behaved as though the cheese was rewarding (decreased latency to eat the pellet), while the ethanol group behaved as though the cheese was aversive (increased latency to eat the pellet). Taken with previous studies, these results demonstrate that posttraining ethanol can have strikingly different effects on retention depending on the task, the measure of retention used, and the underlying neural structures involved.     

Signal-centered action patterns of dogs in appetitive classical conditioning

The movements of five unrestrained dogs were monitored during discriminative Pavlovian conditioning. An auditory-visual stimulus from one source (CS+) was followed by meat morsels (US); the same stimulus from another source (CS?) was not. Sources were equidistant from the site of US delivery. Before each trial, animals were required to position themselves at a starting location equidistant from both sources and removed from the US site. The stable behavior pattern in most subjects included approach to and contact or near contact with CS+, followed by approach to the US site. Dogs showed individually distinctive action patterns to CS+, in some cases suggestive of soliciting, in another of sight-pointing. Similar actions were not evoked by CS?. In postacquisition tests, patterns were generally unaffected by increased deprivation or by relocating the starting position next to the US site. The auditory component of CS+ was more effective than the visual. With a response-contingent procedure animals were successfully trained to approach the US site directly, although many trials, and in one case a special procedure, were required. It was proposed that the experimental signaling arrangement mimics a natural signaling sequence and induces appetitive behavior to the CS that corresponds to the behavior induced by certain natural signals of the US.     

Automated discrete-trials techniques of appetitive conditioning in honey bees

Automated techniques of appetitive conditioning in honey bees are described. The subject is pretrained to come to the laboratory, where it is confined while the training trials are programmed and then is free to return to the hive. The responses recorded are approach to and entering a tube into which sucrose solution is pumped. Illustrative experiments on classical conditioning, simple instrumental conditioning, and choice are reported.     

Spontaneous configuring to a tone-light compound using appetitive training

Rats were trained to bar-press for water in the presence of a simultaneous compound tone-light stimulus using a discrete-trial procedure. Different groups were given between 300 and 3900 trials. When subsequently tested in extinction, all rats showed consistent levels of responding to the compound stimulus but responding to the tone and light components declined as a function of number of training trials. This is a demonstration of spontaneous configuring. Two other experiments showed that with similar procedures generalization from a component of the training stimulus to other values on the same continuum decreases with increased training with the compound stimulus. It was concluded that configuring and generalization from a single stimulus involve the same processes.     

Effect of changing the unconditioned stimulus on appetitive blocking

In four experiments we examined the effects of changing the unconditioned stimulus (US) on appetitive blocking. In Experiments 1A, 1B, and 2 we established that substituting food for water, or water for food, in the compound stage did not attenuate blocking relative to groups that received the same US throughout conditioning. Experiment 3 showed that satiation with the US used prior to compound conditioning with a different US does not affect blocking. Experiment 4 revealed that changing the location of US delivery, as well as the quality of the US, also leaves blocking unaffected. It is suggested that these results demonstrate that blocking occurs, provided that there is no change in the affective properties of the US.     

A molecular dissociation between cued and contextual appetitive learning

In appetitive Pavlovian learning, animals learn to associate discrete cues or environmental contexts with rewarding outcomes, and these cues and/or contexts can potentiate an ongoing instrumental response for reward. Although anatomical substrates underlying cued and contextual learning have been proposed, it remains unknown whether specific molecular signaling pathways within the striatum underlie one form of learning or the other. Here, we show that while the striatum-enriched isoform of adenylyl cyclase (AC5) is required for cued appetitive Pavlovian learning, it is not required for contextual appetitive learning. Mice lacking AC5 (AC5KO) could not learn an appetitive Pavlovian learning task in which a discrete signal light predicted reward delivery, yet they could form associations between context and either natural or drug reward, which could in turn elicit Pavlovian approach behavior. However, unlike wild-type (WT) mice, AC5KO mice could not use these Pavlovian conditioned stimuli to potentiate ongoing instrumental behavior in a Pavlovian-to-instrumental transfer paradigm. These data suggest that AC5 is specifically required for learning associations between discrete cues and outcomes in which the temporal relationship between conditioned stimulus (CS) and unconditioned stimulus (US) is essential, while alternative signaling mechanisms may underlie the formation of associations between context and reward. In addition, loss of AC5 compromises the ability of both contextual and discrete cues to modulate instrumental behavior.In Pavlovian learning, animals form associations between discrete or contextual stimuli in their environment to shape their behavior and make appropriate responses. In discrete cue appetitive Pavlovian conditioning, a single cue with a defined onset and offset that typically activates one sensory modality is provided, immediately followed by reward delivery (Hall 2002; Domjan 2006; Ito et al. 2006). Alternatively, behavior can be driven by context, an assortment of stimuli activating a number of sensory modalities that contribute to the representation of environmental space (Balsam 1985; Rudy and Sutherland 1995; Smith and Mizumori 2006). Collectively, these stimuli make up a context that is paired with reward delivery in contextual appetitive learning. One important distinction between these two forms of learning is that in cued conditioning, there is a discrete temporal relationship between conditioned stimulus (CS) and unconditioned stimulus (US). Thus, an animal can effectively anticipate timing of reward delivery from onset and offset of CS. In vivo studies of dopamine (DA) neuron activity have suggested this discrete temporal relationship can be encoded by DA neurons (Schultz et al. 1997; Schultz 1998a). In contrast, in many contextual Pavlovian conditioning tasks, US delivery is not predicted, it is delivered as the animal explores the environment; thus, the temporal relationship between contextual stimuli and reinforcement is not an essential component of the learned associations (Fanselow 2000). These two types of environmental stimuli may be encoded differently and mediated by different neural substrates.Lesion studies have elucidated the anatomical dissociations between cued and contextual appetitive learning. Using a modified Y-maze procedure, it has been suggested that contextual appetitive learning is hippocampus- and nucleus-accumbens (NAc) dependent, while cued learning is dependent on the basolateral nucleus of the amygdala (BLA) and the NAc (Ito et al. 2005, 2006). In addition, as the NAc processes glutamatergic inputs from the amygdala and the hippocampus (Groenewegen et al. 1999; Goto and Grace 2008), recent studies have indicated that disconnecting the hippocampus from the NAc shell can disrupt contextual appetitive conditioning (Ito et al. 2008). In addition to glutamatergic inputs, the NAc, as part of the ventral striatum, receives dense dopaminergic input from midbrain nuclei (Groenewegen et al. 1999). Temporal shifts in phasic DA release in striatal regions has been correlated with appetitive Pavlovian learning (Day et al. 2007), and models of striatal function suggest that DA-dependent modification of glutamatergic transmission in the striatum may underlie reinforcement learning (Reynolds et al. 2001; Reynolds and Wickens 2002).The cAMP pathway has been implicated in plasticity and learning in a number of neuronal structures (Abel et al. 1997; Ferguson and Storm 2004; Pittenger et al. 2006). Adenylyl cyclase (AC), the enzyme that makes cAMP, has nine membrane-bound isoforms, each with different expression patterns and regulatory properties (Hanoune and Defer 2001). AC5 is highly enriched in the striatum, with very low levels of expression in other regions of the brain (Mons et al. 1998; Iwamoto et al. 2003; Kheirbek et al. 2008, 2009), and genetic deletion of AC5 (AC5KO) severely compromises DA''s ability to modulate cAMP levels in the striatum (Iwamoto et al. 2003). Previous studies have shown that AC5KO mice were severely impaired in acquisition of a cued appetitive Pavlovian learning task, while formation of action–outcome contingencies in instrumental learning was intact (Kheirbek et al. 2008). Yet, it remains unknown whether the cAMP pathway in the striatum underlies all forms of appetitive Pavlovian learning, or how it contributes to the ability of Pavlovian cues to modulate instrumental behavior.In this study, we asked if genetic deletion of AC5 selectively impairs cued or contextual appetitive learning. In addition, we tested whether loss of AC5 affects the ability of conditioned cues or contexts to modulate instrumental behavior. Our data indicate that although loss of AC5 abolishes cued appetitive learning, contextual learning is spared. Although contextual stimuli could elicit approach behavior in AC5KO mice, they could not potentiate an ongoing instrumental response, highlighting the importance of this isoform of AC in Pavlovian–instrumental interactions.     

Analysis of the learned irrelevance effect in appetitive Pavlovian conditioning

In Experiments 1 and 2 rats received uncorrelated presentations of a light conditioned stimulus (CS) and a food unconditioned stimulus (US) on each day of a preexposure phase. Control subjects received the same number of USs during the first half of preexposure and the same number of CSs during the second. Uncorrelated preexposure retarded inhibitory conditioning. Experiment 3 showed, however, that the different patterns of US preexposure experienced by the two groups could in itself influence the course of subsequent inhibitory conditioning. When this factor was equated by restricting the uncorrelated treatment to the first half of the pre-exposure phase (Experiment 2) or by extending the control treatment throughout the phase (Experiment 4) it was found that uncorrelated preexposure retarded excitatory conditioning, but facilitated inhibitory conditioning. This outcome challenges an interpretation in terms of the concept of learned irrelevance, which predicts that uncorrelated preexposure should retard both forms of conditioning.     

Aversive and appetitive electrodermal classical conditioning using pictures as stimuli

The principal goal of this study was to verify whether it was possible to obtain both aversive and appetitive electrodermal classical conditioning, using pictures as conditioned stimuli (CS), and unconditioned stimuli (US). Additionally, we tried to verify whether, as a consequence of such conditioning, diminution of the unconditioned response (UR) was observed. With this aim, IAPS (?International Affective Picture System?) pictures were selected as stimuli. A picture showing a burnt face was used as the aversive US (USav), and a picture showing a scene with erotic content was used as the appetitive US (USap). As the aversive CS (CSav), and appetitive CS (CSap), two images with intermediate values of valence and arousal showing male faces were selected. In the experimental group, 10 CSav/USav and 10 CSap/USap trials were presented. In the control group 10 CSav, CSap, USav, and USap trials were presented in pseudorandom order. Skin conductance response (SCR) elicited by both the CSs and the USs was scored. Results showed aversive conditioning, but neither appetitive conditioning nor UR diminution. Problems to obtain conditioning using pictures as stimuli and possible options to overcome them in future research are discussed.     

Enhancement of food-rewarded instrumental responding by an appetitive conditioned stimulus

Four experiments are reported in which a stimulus (with a minimum duration of 60 s) signalling the delivery of “free” food was presented to rats lever-pressing for food available on a variable interval schedule. It was found that responding was enhanced in the presence of the stimulus when the baseline schedule of reinforcement was lean (Experiment I) and that the enhancement was dependent upon the pairing of the stimulus with free food (Experiments II and III). Experiment IV showed that an enhancement could be found after initial training in which stimulus-food pairings were given to subjects that were not concurrently lever pressing for food. It is argued that these results are consistent with the suggestion that an appetitive conditioned stimulus can energise appetitive instrumental behaviour.