Pavlovian heart rate and jaw movement conditioning in the rabbit: effects of medial prefrontal lesions

Cardiac response in aversive and appetitive olfactory conditioning: Evidence for a valence-independent CS-elicited bradycardia

While the examination of conditioned cardiac responses is well established in human fear conditioning research, comparable studies using less-aversive or rather appetitive unconditioned stimuli (UCS) are sparse and results are mixed. Therefore, the aim of this study was a systematic analysis of cardiac reactions in aversive and appetitive conditioning. Olfactory stimuli were used as unconditioned stimuli as they are suitable reinforcers in both an aversive and an appetitive conditioning offering the opportunity for a comparison between conditioned responses. In total, n = 86 participants took part in both an aversive and an appetitive differential conditioning task with a counterbalanced order across participants. Aversive or appetitive odors, respectively, served as UCS and neutral geometrical figures as CS. Subjective ratings, skin conductance response (SCRs), and evoked cardiac reactions were analyzed and compared between tasks. Conditioned responses in subjective ratings could be observed in both aversive conditioning and appetitive conditioning, while SCRs discriminated between CS+ and CS- in aversive conditioning only. Regarding conditioned cardiac responses, the deceleration for the CS+ was longer than for the CS- in both tasks. In addition, a higher deceleration magnitude and a shorter acceleration for the CS+ as compared to the CS- were found in aversive but not in appetitive conditioning. There were medium-size correlations between aversive and appetitive CRs for subjective ratings and none for physiological responses. The results suggest similarities between cardiac response patterns in aversive and appetitive conditioning, which implies that bradycardia in conditioning might not be fear-specific but presents a valence-independent CS-elicited bradycardia.

Development of a Classical Conditioning Task for Humans Examining Phasic Heart Rate Responses to Signaled Appetitive Stimuli: A Pilot Study

Cardiac responses to appetitive stimuli have been studied as indices of motivational states and attentional processes, the former being associated with cardiac acceleration and latter deceleration. Very few studies have examined heart rate changes in appetitive classical conditioning in humans. The current study describes the development and pilot testing of a classical conditioning task to assess cardiac responses to appetitive stimuli and cues that reliably precede them. Data from 18 adults were examined. They were shown initially neutral visual stimuli (putative CS) on a computer screen followed by pictures of high-caloric food (US). Phasic cardiac deceleration to food images was observed, consistent with an orienting response to motivationally significant stimuli. Similar responses were observed to non-appetitive stimuli when they were preceded by the cue associated with the food images, suggesting that attentional processes were engaged by conditioned stimuli. These autonomic changes provide significant information about classical conditioning effects in humans.

Using internal memory representations in associative learning to study hallucination-like phenomenon

Studies of Pavlovian conditioning have enriched our understanding of how relations among events can adaptively guide behavior through the formation and use of internal mental representations. In this review, we illustrate how internal representations flexibly integrate new updated information in reinforcer revaluation to influence relationships to impact actions and outcomes. We highlight representation-mediated learning to show the similarities in properties and functions between internally generated and directly activated representations, and how normal perception of internal representations could contribute to hallucinations. Converging evidence emerges from recent behavioral and neural activation studies using animal models of schizophrenia as well as clinical studies in patients to support increased tendencies in these populations to evoke internal representations from prior associative experience that approximate hallucination-like percepts. The heightened propensity is dependent on dopaminergic activation which is known to be sensitive to hippocampal overexcitability, a condition that has been observed in patients with psychosis. This presents a network that overlaps with cognitive neural circuits and offers a fresh approach for the development of therapeutic interventions targeting psychosis.

Reevaluating the role of the medial prefrontal cortex in delay eyeblink conditioning

It has been proposed that the medial prefrontal cortex (mPFC) is not necessary for delay eyeblink conditioning (DEC). Here, we investigated the involvement of the mPFC in DEC with a soft or loud tone as the conditioned stimulus (CS) by using electrolytic lesions or muscimol inactivation of guinea pig mPFC. Interestingly, when a soft tone was used as a CS, electrolytic lesions of the mPFC significantly retarded acquisition of the conditioned response (CR), and muscimol infusions into mPFC distinctly inhibited the acquisition and expression of CR, but had no significant effect on consolidation of well-learned CR. In contrast, both electrolytic lesions and muscimol inactivation of mPFC produced no significant deficits in the CR when a loud tone was used as the CS, or in the unconditioned response (UR) when a soft or loud tone was used as the CS. These results demonstrate that the mPFC is essential for the DEC with the soft tone CS but not for the DEC with the loud tone CS.

The cardiac response of the crab Chasmagnathus granulatus as an index of sensory perception

When an animal's observable behavior remains unaltered, one can be misled in determining whether it is able to sense an environmental cue. By measuring an index of the internal state, additional information about perception may be obtained. We studied the cardiac response of the crab Chasmagnathus to different stimulus modalities: a light pulse, an air puff, virtual looming stimuli and a real visual danger stimulus. The first two did not trigger observable behavior, but the last two elicited a clear escape response. We examined the changes in heart rate upon sensory stimulation. Cardiac response and escape response latencies were also measured and compared during looming stimuli presentation. The cardiac parameters analyzed revealed significant changes (cardio-inhibitory responses) to all the stimuli investigated. We found a clear correlation between escape and cardiac response latencies to different looming stimuli. This study proved useful to examine the perceptual capacity independently of behavior. In addition, the correlation found between escape and cardiac responses support previous results which showed that in the face of impending danger the crab triggers several coordinated defensive reactions. The ability to escape predation or to be alerted to subtle changes in the environment in relation to autonomic control is associated with the complex ability to integrate sensory information as well as motor output to target tissues. This ;fear, fight or flight' response gives support to the idea of an autonomic-like reflexive control in crustaceans.

Single unit activity in the medial prefrontal cortex during pavlovian heart rate conditioning: Effects of peripheral autonomic blockade

Electrical activity was recorded from single neurons in the medial prefrontal cortex of rabbits during differential Pavlovian heart rate (HR) conditioning. A heterogeneous population of cells were found, some of which showed CS-evoked increases and others CS-evoked decreases in discharge, while some cells were biphasic. A subset of cells also showed trial-related changes in discharge that were related to acquisition of the HR discrimination between the reinforced CS+ and non-reinforced CS-. Administration of the peripheral cholinergic antagonist, methylscopolamine, and the andrenergic antagonist, atenolol, either increased or decreased maintained baseline activity of many cells, but had little or no effect on the CS-evoked activity of these cells. Waveform changes also did not result from administration of these drugs. This finding suggests that CS-evoked mPFC activity is not being driven by cardiac afferent input to CNS cardiac control centers. Previous studies have shown that ibotenic acid lesions of this area greatly decreases the magnitude of decelerative heart rate conditioned responses; the latter finding, plus the results of the present study, suggest that processing of CS/US contingencies by the prefrontal cortex contributes to the acquisition of autonomic changes during Pavlovian conditioning.

Cardiovascular component of the context signal memory in the crab Chasmagnathus

Research on diverse models of memory in vertebrates demonstrates that behavioral, autonomic and endocrine responses occur together during fear conditioning. With invertebrates, no similar studies have been performed despite the extensive study of fear memory paradigms, as the context signal memory (CSM) of the crab Chasmagnathus granulatus, usually assessed by a behavioral parameter. Here, we study the crab's CSM, considering both the behavioral response and the concomitant neuroautonomic adjustments resulting in a heart rate alteration. Results show that upon the first presentation of the visual danger stimulus, a heart arrest followed by bradycardia is triggered together with a conspicuous escape response. The latter declines throughout training, while heart arrests become sporadic and bradycardia tends to deepen along the session. At test, 24 h after training, the outcome clearly contrasts with that shown at training, namely, stimulus presentation in the same context induces lower escape, no heart arrests and quick suppression of bradycardia. These results support the view that the same memory process brings about the changes in both responses. High escape, heart arrest and bradycardia are considered three parameters of the unconditioned response while minor escape, no heart arrests and bradycardia attenuation are three parameters of the learned response.

The role of claustrum in Pavlovian heart rate conditioning in the rabbit (Oryctolagus cuniculus): anatomical, electrophysiological, and lesion studies

The role of the claustrum in Pavlovian heart rate (HR) conditioning was studied in the rabbit (Oryctolagus cuniculus) by (a) mapping claustral projections to the prefrontal cortex (PFC), (b) recording claustral single-unit discharge to sensory stimulation and conditioning stimuli during HR conditioning, and (c) assessing the effects of claustral damage on HR conditioning. Contralateral and ipsilateral claustral projections to the PFC were found. Claustral cells responded to nonsignal stimulation with increased discharge and also showed conditioned stimulus-evoked increases in discharge during Pavlovian HR conditioning. Moreover, claustral lesions diminished the magnitude of the HR-conditioned response without affecting the cardiac-orienting response to the conditioned stimulus or the cardiac-unconditioning response to the unconditioned stimulus, suggesting a role for the claustrum in associative learning.

C-fos activation patterns in rat prefrontal cortex during acquisition of a cued classical conditioning task

The prefrontal cortex (PFC) is known to be involved in associative learning; however, its specific role in acquisition of cued classical conditioning has not yet been determined. Furthermore, the role of regional differences within the PFC in the acquisition of cued conditioning is not well described. These issues were addressed by exposing rats to either one or four sessions of a cued classical conditioning task, and subsequently examining c-fos immunoreactivity in various areas of the PFC. Differences in patterns of c-fos immunopositive nuclei were found when comparing the PFC areas examined. No significant differences were found between rats presented with a temporally contingent conditioned stimulus (CS) light and food (paired groups) and those presented with the same stimuli temporally non-contingently (unpaired groups). In lateral and orbital PFC, both the paired and unpaired groups showed more c-fos immunopositive nuclei than control groups exposed only to the behavioral setup (context exposed groups), and all groups showed a drop in c-fos immunopositive nuclei from session 1 to session 4. In dorsal medial PFC, no differences were seen between the paired, unpaired and context exposed groups. These groups did, however, differ from naive animals, an effect that was not seen in the ventral medial PFC. The results of this study do not support a role for the PFC in the acquisition of a cued classical conditioning task. The differences seen between paired, unpaired and context exposed groups in orbital and lateral PFC could be due to contextual conditioning or reward-related effects.

Heart rate changes accompanying jaw movement Pavlovian conditioning in rabbits: concomitant blood pressure adjustments and effects of peripheral autonomic blockade

Two experiments were conducted to ascertain the cardiovascular accompaniments of differential Pavlovian jaw movement (JM) conditioning. The first examined the blood pressure (BP) changes that accompany the tachycardiac conditioned responses (CRs) associated with JM conditioning. The BP response in all instances consisted of a depressor response that was greater to the reinforced CS+ than CS-, although the magnitude of the CR was quite small. The second experiment determined the effects of peripheral autonomic antagonists on the cardiac accelerations associated with JM conditioning. It was found that the peripheral vagal antagonist methyl scopolamine completely abolished responses to both CS+ and CS-, whereas atenolol, a beta adrenergic antagonist, augmented the response, compared to saline control injections. The JM responses were also affected by the autonomic blockades, with minimal responding occurring in the scopolamine group but slightly more JM CRs in the atenolol group, compared to saline control animals. These results suggest that the major cardiovascular response to an appetitive stimulus, which evokes JM conditioning, consists of cardiac accelerations with the BP depressor responses playing a minimal, if any, role. Moreover, these conditioned cardiac increases appear to be due solely to the release of vagal inhibition.

Characterization of the neuronal changes in the medial prefrontal cortex during jaw movement and eyeblink Pavlovian conditioning in the rabbit

Medial prefrontal (mPFC) single-unit activity was assessed in defensive (eyeblink, EB) and appetitive (jaw movement, JM) Pavlovian conditioning in the rabbit. Concomitant heart rate (HR) changes were also assessed. In a first experiment robust JM conditioned responses (CRs) were observed to a tone-water (CS+) contingency but not to tone-alone (CS-), indicating discriminative JM conditioning. However, the CS-evoked accelerative HR response was not discriminative. Nevertheless, several single-unit discharge patterns were evoked by both tone-water and tone-alone, many of which were uniquely associated with either the CS+ or CS-. In a second experiment, Three separate stimuli, consisting of tone followed by periorbital shock (tone-shock), water (tone-water), and white noise not followed by shock or water, were presented in the same paradigm. Discrimination of conditioned JM, EB and HR changes were observed, i.e. each of these behavioral responses were uniquely associated with the relevant CS presentation. Conditioned bradycardia was evoked by tone-water during the first training session, which changed to tachycardia with further training. However, conditioned bradycardia was evoked by tone-shock throughout training. Different subpopulations of mPFC cells were activated by the tone-shock and tone-water contingencies, but a small group of cells were activated by both.

Hippocampal theta oscillations and classical conditioning

Studies are reviewed that support a hypothesized role for hippocampal theta oscillations in the neural plasticity underlying behavioral learning. Begun in Richard F. Thompson's laboratory in the 1970s, these experiments have documented a relationship between free-running 3- to 7-Hz hippocampal slow waves (theta) and rates of acquisition in rabbit classical nictitating membrane (NM) conditioning. Lesion and drug manipulations of septohippocampal projections have affected NM and jaw movement conditioning in ways consistent with a theta-related brain state being an important modulator of behavioral acquisition. These findings provide essential empirical support for the recently developed neurobiological and computational models that posit an important role for rhythmic oscillations (such as theta) in cellular plasticity and behavioral learning.

Neurotoxic lesions of the dorsal hippocampus disrupt auditory-cued trace heart rate (fear) conditioning in rabbits

The first experiment in this study used the classical heart rate (HR) conditioning paradigm to determine if rabbits could associate an auditory conditioned stimulus (CS) and a fear-producing shock-unconditioned stimulus (US) separated by an empty 10-s trace interval. Trace conditioned rabbits (n = 7) acquired significant bradycardiac conditioned HR responses on CS-alone test trials during a single 35-trial conditioning session. Control animals (n = 7) which received unpaired CSs and USs did not show HR conditioning. During a retention session of CS-alone trials 24 h after the conditioning session, some trace-conditioned animals showed conditioned HR responses immediately following CS onset (n = 3), while others showed responses appropriately timed to the US onset (n = 4) used in trace conditioning 24 h earlier. Thus, rabbits remember the duration of the long 10-s trace interval 24 h after a single day of training. The second part of this study sought to determine if cells in the dorsal hippocampus play a role in trace HR conditioning. Rabbits were given bilateral ibotenic acid lesions in the neocortex (n = 7) or dorsal hippocampus (n = 8). During trace conditioning and retention, neocortical animals showed conditioned HR responses to the CS, whereas the hippocampal group showed no significant HR conditioning. One week after trace conditioning, the same animals received a delay HR conditioning session where no trace interval separated the CS and US. During delay conditioning, hippocampal animals showed significant conditioned HR responses to the CS that were similar to the neocortical group. Thus, the dorsal hippocampus plays a critical role in rabbit HR conditioning when the CS and US are separated by a 10-s trace interval. This paradigm may be ideal for in vivo electrophysiological recording studies because rabbits are easily immobilized during the testing procedure, and learning occurs during a single day of training.

Expression of Fos-related antigens in the nucleus accumbens and associated regions following exposure to a cocaine-paired environment

This study examined whether conditioned hyperactivity measured in a cocaine-paired environment was associated with increased expression of Fos-related antigens (FRA) within the nucleus accumbens (NAc) and associated forebrain regions of rats. Three groups of rats were given repeated injections of either cocaine in the test environment and saline in the colony room (group Paired), saline in the test environment and cocaine in the colony room (group Unpaired), or saline in both environments (group Control). All rats were subsequently given a drug-free test for conditioned hyperactivity in the test environment, and their brains were removed so that FRA immunohistochemistry could be conducted. Rats in the Paired group showed conditioned hyperactivity during the conditioning test, and this behavioural response was associated with increased FRA expression within the caudal NAc, the medial prefrontal cortex and the lateral septum relative to the Unpaired and Control groups. Paired rats also showed increased FRA expression within the orbital prefrontal cortex, the claustrum, the caudal amygdala (basolateral and central regions), the paraventricular thalamic nucleus, the subiculum of the hippocampus, and the lateral habenula relative to the Control group. However, the FRA levels in these latter sites were not significantly increased relative to those of Unpaired rats, indicating that genomic responses in these regions were not entirely context dependent. The correspondence between conditioned hyperactivity and enhanced FRA expression within the caudal NAc, the medial prefrontal cortex and lateral septum suggests that these regions may participate in the expression of conditioned responses to cocaine-related stimuli.

A behavioral stages model of classical (Pavlovian) conditioning: application to cognitive aging

In the present article, it is argued that a five-stage sequential model of the behavioral and neurophysiological events that occur when organisms are exposed to signals predicting significant events suggests that classical conditioning produces multiple memory traces involving both excitatory and inhibitory processes. Further, these multiple brain structures and associated neurophysiological mechanisms are beginning to be understood; thus, using Pavlovian conditioning techniques to study aging and cognitive functions may provide insights into which brain structures or mechanisms are responsible for more general age-related declines in associative learning and memory. The evidence for this model is briefly reviewed and studies suggesting age-related effects on classical conditioning of various response systems are described within the context of the brain structures implicated by the model.