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PubMed1996

Classical conditioning of electrical self-stimulation of ventral tegmental area to brief visual stimuli in rats.

Two groups of rats with bipolar electrodes implanted unilaterally into the left ventral tegmental area were trained to lever-press for the response contingent electrical stimulation. After preliminary lever-press training, two types of daily sessions were held on 10 consecutive days: type T+, current intensity set at the Threshold level and each response was accompanied by the visual signal (stimulus lights above the lever briefly went off): and type ST-, current set at the Sub Threshold level and no visual stimuli. On day 11, combination of the subthreshold current intensities and stimulus lights previously associated with the threshold stimulation (session type ST+) resulted in a significantly elevated response rates compared to the performance under the subthreshold current without visual stimuli (session type ST-). The extinction and recovery of this phenomenon are also demonstrated.

Animals↗
PubMed1992

Classical conditioning after temporal lobe lesions in man: sparing of simple discrimination and extinction.

Recent reports of impaired conditional discrimination learning in temporal lobectomy subjects have raised the question of response inhibition deficits in these patients. In the present study, left and right temporal lobectomy subjects and healthy controls completed an eyelid conditioning task, which required simple two-tone discrimination learning, followed by extinction. There were no group differences with regard to discrimination learning or extinction. General deficits in response inhibition are therefore not likely to account for the impairment in conditional discrimination observed in temporal lobectomy patients.

Acoustic Stimulation↗
PubMed1989

The interstimulus interval and classical conditioning in the marine snail Hermissenda crassicornis.

We examined the role of the interstimulus interval for the conditioned association between light and rotation stimuli in the marine snail Hermissenda. This interval between the conditioned stimulus (CS) and the unconditioned stimulus (US) is an important and widespread property of vertebrate associative learning. We demonstrated that with a forward CS-US delay of 1.0 s we were able to produce significant 24-h retention of an associative memory after 50 training trials. Other paired treatments providing intervals of 1.5 s, 0.5 s, simultaneous, and backward arrangements did not support retention at 24 h.

Animals↗
PubMed2000

Classically conditioned responses following repeated insulin and glucose administration in humans.

This paper describes the neural basis and the role of Pavlovian conditioning in the modification of blood glucose and related endocrine parameters after repeated insulin and glucose administration. Pavlovian conditioning requires that conditioned stimulus (CS) and unconditioned stimulus (US) are both detected in the central nervous system (CNS), where the CS-US association takes place. We will therefore elucidate the detectability of insulin and glucose in the CNS. Since current data focus almost exclusively on animals, we conducted a placebo-controlled insulin conditioning experiment in humans (Experiment 1). Compared with the control group with CS-placebo pairings throughout, the experimental group with previous CS-insulin pairings in the acquisition phase showed a conditioned decrease in blood glucose and a trend for a conditioned baseline insulin increase, and an increase in cortisol levels relative to baseline and cumulative number of neuroglycopenic symptoms in the CS-placebo test session. The conditionability of glucose administration also had to be examined; experiments using an arbitrary CS and glucose are extremely rare, even in animals. Glucose is the natural stimulus for endogenous insulin secretion, so studies on cephalic-phase insulin release (CPIR) will be reviewed in this paper. We implemented a placebo-controlled three-group design (Experiment 2): Subjects received either CS-insulin, CS-glucose or CS-placebo pairings during the acquisition. Together, our results demonstrate the conditionability mainly of insulin, but also of glucose effects in healthy humans. The clinical relevance and future research perspectives are outlined with an emphasis on insulin in the brain and its role in learning and memory.

Conditioning, Classical↗
PubMedDate not supplied

Nimodipine ameliorates impaired eyeblink classical conditioning in older rabbits in the long-delay paradigm.

Research using the hippocampally dependent short-conditioned stimulus trace conditioning paradigm demonstrated that nimodipine ameliorated learning deficits in older rabbits. Evidence from in vitro and in vivo measures indicated that the site of drug action was hippocampal pyramidal cells. Acquisition occurs in the long (750 ms) delay conditioning paradigm in the absence of the hippocampus. This experiment with 40 older rabbits was undertaken to determine if nimodipine ameliorates impaired acquisition in a conditioning paradigm not dependent on the hippocampus. Fifteen 90-trial sessions of paired conditioning stimuli were presented to 3 groups receiving daily injections of 0, 1, or 5 mg/kg nimodipine. Explicitly unpaired control groups received 0 or 5 mg/kg nimodipine. Acquisition with the 5 mg/kg dose was significantly faster. Existing evidence suggested that nimodipine acted in the hippocampus, but we could not rule out the possibility that the drug also affected conditioning via the cerebellum.

Aging↗
PubMed2003

The novel dopamine D4 receptor agonist (PD 168,077 maleate): doses with different effects on locomotor activity are without effect in classical conditioning.

Conditioning is normally selective to the most likely predictors of motivationally significant events and some dopamine (DA) agonists produce dysfunction in this process. Moreover, the DA D(4) receptor is implicated in normal and abnormal functions that have some dopaminergic basis (e.g., in attention deficit hyperactivity disorder and schizophrenia). We therefore used locomotor activity to identify doses of a novel D(4) receptor agonist (PD 168,077) with contrasting behavioral effects (over the range 0.064-1 mg/kg). Doses that either did (0.064 mg/kg) or did not (0.5 mg/kg) significantly increase activity were then tested using aversive and appetitive procedures, in which conditioning was reflected in decreased and increased response rates, respectively. Associating a signal with food or foot shock is normally reduced in trace conditioning, when stimulus events are separated in time. Similarly, animals normally learn relatively little about background stimuli that do not well predict food delivery or the onset of shock. Both doses of PD 168,077 were without effect on conditioning, whether appetitive or aversive, and irrespective of how informative the predictive stimulus was. Thus, we find no evidence that the D(4) receptor has any likely effect on associative learning or its disorder. Furthermore, D(4)-mediated hyperactivity was dissociable from cognitive effects.

Animals↗
PubMed1999

Effects of CS-US interval modification on diminution of the unconditioned response in electrodermal classical conditioning.

The purpose of this experiment was to study whether interstimulus interval (ISI) modification differentially affects the amplitude of the unconditioned response (UR amp.). Seventy-five volunteer subjects received discrimination training with an interval between conditioned stimulus (CS) and unconditioned stimulus (US; aversive white noise) of 8 s. After the discrimination training phase, subjects exhibiting discriminative control were randomized into three groups that differed according to the ISI, of 1, 5 or 8 s. The subjects of each group were then tested with five presentations of CS + /US. The results demonstrate that the UR showed a greater amplitude when an ISI of 8 s was used than with ISIs of 1 or 5 s. No significant differences were found between the UR amp. of the 1- and 5-s ISI groups. These findings are discussed as a result of a hypothetical experimentally induced blend of the anticipatory CRs with the UR.

Adult↗
PubMed1997

Classical conditioning and the placebo effect.

Stimulus substitution models posit that placebo responses are due to pairings of conditional and unconditional stimuli. Expectancy theory maintains that conditioning trials produce placebo response expectancies, rather than placebo responses, and that the expectancies elicit the responses. We tested these opposing models by providing some participants with information intended to impede the formation of placebo expectancies during conditioning trials and by assessing placebo expectancies. Although conditioning trials significantly enhanced placebo responding, this effect was eliminated by adding expectancies to the regression equation, indicating that the effect of pairing trials on placebo response was mediated completely by expectancy. Verbal information reversed the effect of conditioning trials on both placebo expectancies and placebo responses, and the magnitude of the placebo effect increased significantly over 10 extinction trials. These data disconfirm a stimulus substitution explanation and provide strong support for an expectancy interpretation of the conditioned placebo enhancement produced by these methods.

Adolescent↗
PubMed1999

Hippocampus and context in classical conditioning.

Recent evidence suggests that contextual learning encompasses a variety of changes in learning and performance processes. Only some of these changes depend on the hippocampus. Specialized functions proposed for the hippocampus in contextual learning include the construction and consolidation of contextual memory representations, incidental contextual learning, and inhibitory contextual learning.

Animals↗
PubMed1976

Information about the model's unconditioned stimulus and response in vicarious classical conditioning.

Four groups with 16 observers each participated in a differential, vicarious conditioning experiment with skin conductance responses as the dependent variable. The information available to the observer about the model's unconditioned stimulus and response was varied in a 2 X 2 factorial design. Results clearly showed that information about the model's unconditioned stimulus (a high or low dB level) was not necessary for vicarious instigation, but that information about the unconditioned response (a high or low emotional aversiveness) was necessary. Data for conditioning of responses showed almost identical patterns to those for vicarious instigation. To explain the results, a distinction between factors necessary for the development and elicitation of vicariously instigated responses was introduced, and the effectiveness of information about the model's response on the elicitation of vicariously instigated responses was considered in terms of an expansion of Bandura's social learning theory.

Adult↗
PubMed1985

Effect of classical conditioning on an internal clock.

Six experiments with rats used a psychophysical choice procedure to study the internal clock used to discriminate duration. They investigated if the clock is sensitive to the signal value (associative strength) of a stimulus. The experiments involved two types of trials. On choice trials, a stimulus lasted a short (e.g., 3 s) or long (e.g., 12 s) duration; then the rats chose between two levers. The rewarded choice depended on the duration of the stimulus. On conditioning trials, the stimulus used on choice trials was presented, but it ended without food (extinction trials) or with food (pairing trials) regardless of what the rat did. The main stimulus minus accuracy with the long stimulus. Experiment 1 showed that extinction trials increased short bias relative to training without conditioning trials or to training with pairing trials. The rest of the experiments tested explanations of these results. The same results were found when extinction trials were the same duration as the short stimulus (Experiment 2), when extinction trials were a random duration (Experiment 5), and when the signal value of the conditioned stimulus was changed in another way (Experiment 6). The effect of conditioning trials was modality specific (Experiments 3 and 4). Of the explanations considered, the best one--the only one not contradicted at least once--is that changing the signal value of a stimulus changes how the clock times the stimulus. Reducing signal value reduces the measured duration.

Animals↗
PubMed2000

Stimulus and temporal cues in classical conditioning.

In 2 experiments, separate groups of rats were given stimulus conditioning, temporal conditioning, untreated control and (in Experiment 2) learned irrelevance control procedures, followed by a compound with both stimulus and temporal cues. Stimulus conditioning consisted of a random 15-s duration conditioned stimulus (CS) followed by food; temporal conditioning consisted of food-food intervals of fixed 90 s (Experiment 1) or fixed 75 + random 15 s (Experiment 2). The stimulus group abruptly increased responding after CS onset, and the temporal group gradually increased responding over the food-food interval. When the food-food interval was fixed 90 s, the temporal cue exerted stronger control in the compound, whereas when the food-food interval was fixed 75 + random 15 s, the stimulus cue exerted stronger control. The strength of conditioning, temporal gradients of responding, and cue competition effects appear to reflect simultaneous timing of multiple intervals.

Animals↗
PubMed1986

Behaviorally functional opioid systems in infant rats: I. Evidence for olfactory and gustatory classical conditioning.

In order to characterize behavioral function of opioid systems in neonatal rats, two series of experiments were initiated. In one, the reinforcing properties of exogenous opioids were investigated in 5-day-old pups. Specifically, the infant's ability to associate the novel taste of saccharin, received while suckling, with ip morphine injections was assessed. Rats that received 0.5 ml of saccharin prior to morphine administration ingested considerably more saccharin on Day 10 than did control rats. The second set of experiments was conducted to determine whether rat pups could associate a novel odor with morphine administration. Five days after conditioning, that stimulus was highly preferred by morphine-treated pups compared with saline control pups. Thus positive associations were formed with either a novel taste stimulus experienced while suckling or with an odor experienced during social isolation. Conditioning was cue specific and was retained for at least 5 days. The formation of these associations was blocked with opioid antagonists given prior to conditioning. These data suggest behaviorally functional opioid receptors and raise the possibility of a functional role of the endogenous opioids in motivational processes in infant rats.

Animals↗
PubMed1988

Stimulation of the spinal trigeminal nucleus supports classical conditioning of the rabbit's nictitating membrane response.

Acquisition, extinction, and differential conditioning of the rabbit's nictitating membrane response to a tone conditioned stimulus were supported by electrical stimulation of the spinal trigeminal nucleus. Stimulation of the accessory abducens nucleus, the abducens nucleus, and the reticular formation at the level of the spinal trigeminal nucleus supported lower, transient levels of conditioning. The results are discussed in terms of stimulation of sensory inputs to the brainstem and cerebellum.

Animals↗
PubMed1991

Effects of centrally administered anxiolytic agents on classically conditioned bradycardia.

Rats received infusions of the opioid peptide D-Ala2-Met-enkephalinamide (DALA, 10 micrograms), the alpha 2-noradrenergic agonist clonidine (CLON, 3 micrograms), UK14,304 (UK, 5 micrograms), the corticotropin-releasing factor (CRF) antagonist alpha-helical CRF (9-41) (alpha-HEL, 25 micrograms), or saline in the rostral fourth ventricle. The DALA, CLON, and UK groups showed no evidence of a heart rate (HR) conditioned response (CR) during conditioning, after antagonist administration, or on a nondrug test 48 hr after conditioning. These three groups showed the development of normal CRs when later retrained without drugs. The alpha-HEL group showed an enhanced CR. During a subsequent startle test, the presence of a conditioned stimulus resulted in a pronounced suppression of startle in the SAL and alpha-HEL groups but had no effects on startle in the DALA, CLON, and UK groups. The results indicate an important role for fourth ventricle structures containing opioid and alpha 2 receptors in the learning of an HR CR.

Animals↗
PubMed1994

Classical conditioning of opioid activity in the fetal rat.

Milk promotes activity in the kappa opioid system of the rat fetus that reduces responsiveness to cutaneous stimulation. In this study, fetuses on Gestational Day 20 were presented with an artificial nipple (conditioned stimulus; CS) paired with an intraoral infusion of milk (unconditioned stimulus; US). One paired presentation of the CS and US reduced fetal responsiveness after reexposure to the CS. Selective antagonism of opioid receptors after conditioning indicated that reduced responsiveness was due to mu opioid activity. Mu and kappa opioid activity was evident after 3 paired presentations of CS and US and reexposure to milk. Kappa opioid activity during conditioning was necessary for mu involvement after reexposure to the CS or US. These experiments, which were conducted with fetal subjects that lacked suckling experience, suggest that neurochemical systems engaged during suckling may change rapidly after the newborn's initial experiences at the nipple.

Animals↗
PubMed1996

Classical conditioning with electrical stimulation of cerebellum as both conditioned and unconditioned stimulus.

Stimulating electrodes were implanted in rabbit cerebellum, providing an electrical conditioned stimulus (CS) activating cortical parallel fibers and thence Purkinje and other cells, and an electrical unconditioned stimulus (US) activating underlying white matter and eliciting unconditioned responses. Paired CS-US presentations led to the development of conditioned responses, which showed extinction following CS-alone trials and reacquisition with significant savings on reinstatement of paired trials. Increased local excitability as a result of paired training (but not following unpaired stimulus presentations) was observed in cerebellar cortex, as manifested in substantial decreases in CS threshold for response elicitation in all subjects. This preparation offers a model for the study of plastic neuronal interactions within cerebellar networks critically involved in associative learning.

Animals↗