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Results for “CONDITIONED LEARNING”

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PubMed1980

Retention under changed-reward conditions of persistence learned by infant rats.

Two experiments were performed to determine whether or not persistence acquired under reinforcement conditions of infancy can be retained and transferred to adult reinforcing conditions. In Experiment I 2 groups of rats 14-15 days of age were trained in a runway under a partial (PRF) or continuous (CRF) schedule of milk-suckling reinforcement. A 3rd group was trained under continuous nonreinforcement (NRF) conditions. The PRF and CRF groups acquired the approach response about equally, and the NRF showed a very small increase in speed. In immediate extinction, the PRF group was more resistant to extinction than its CRS counterpart. For the NRF group "extinction" produced a continuation of the low-level "acquisition" performance. Experiment II showed that persistence acquired at 14-15 days with milk-suckling reinforcement can be sustained through a 2-week retention period including a phase of CRF food-pellet reward.

Aging↗
PubMed1986

Mechanisms of radiation-induced conditioned taste aversion learning.

The literature on taste aversion learning is reviewed and discussed, with particular emphasis on those studies that have used exposure to ionizing radiation as an unconditioned stimulus to produce a conditioned taste aversion. The primary aim of the review is to attempt to define the mechanisms that lead to the initiation of the taste aversion response following exposure to ionizing radiation. Studies using drug treatments to produce a taste aversion have been included to the extent that they are relevant to understanding the mechanisms by which exposure to ionizing radiation can affect the behavior of the organism.

Amphetamine↗
PubMed1999

Insular cortex lesions and taste aversion learning: effects of conditioning method and timing of lesion.

The specific role of insular cortex in acquisition and expression of a conditioned taste aversion was assessed using two different conditioning methods, which vary mode of taste delivery. Involvement of insular cortex in the induction of c-Fos-immunoreactivity in the nucleus of the solitary tract, a cellular correlate of the behavioral expression of a conditioned taste aversion, was also assessed. Electrolytic lesions of insular cortex blocked behavioral expression of a conditioned taste aversion and this was evident not only when lesions were placed prior to conditioning, but also when they were made after conditioning but before testing. In contrast to the effects on behavior, lesions did not completely block the c-Fos-immunoreactivity which accompanies re-exposure to the aversive taste. In addition, the blocking of behavioral evidence of aversion conditioning by cortical lesions was seen both in animals trained under an intraoral acquisition procedure and those trained with bottle-conditioning. This contrasts with previous work with amygdala lesions which showed that amygdala was absolutely necessary for taste aversions conditioned with the intraoral method but not for those conditioned using bottle presentation of the taste. Overall, these findings imply that the details of the neural circuitry involved in taste aversion learning, including its anatomical distribution, complexity and degree of redundancy, vary with the type of conditioning method employed.

Amygdala↗
PubMed1995

Potentiation or depression of synaptic efficacy in the dentate gyrus is determined by the relationship between the conditioned and unconditioned stimulus in a classical conditioning paradigm in rats.

Learning a conditioned stimulus (CS)-unconditioned stimulus (US) association is accompanied by a variety of long-lasting changes in physiology and chemistry of the synapse in the dentate gyrus. To determine the time course of synaptic modification during learning, changes in the perforant path-dentate gyrus-evoked field potentials were measured in rats performing a classical conditioning (paired tone and footshock) or pseudoconditioning (unpaired tone and footshock) task. Over the course of 4 days of training, differential changes in the evoked response were observed in the two groups. In the conditioned group, there was an increase in the slope of the excitatory postsynaptic potential (EPSP) which started after five tone-shock paired trials and lasted for more than 40 min, outlasting the training session by 20 min. In contrast, a decrease in the slope of the EPSP which commenced after training and lasted for at least 1 h was observed in the pseudoconditioned group. In both groups there was a prolonged decrease in the amplitude of the population spike. The increase in the EPSP was reduced and the duration tended to shorten over days of training in the conditioned group, whereas in the pseudoconditioned group the decrease in the EPSP tended to increase. Off-line analysis of suppression of lever-pressing for food reward during the presentation of the tone, indicated that the conditioned rats had learned the tone-footshock association. Temperature was measured in the dentate gyrus of rats undergoing an identical procedure. In both groups slight temperature increases were observed, with no difference in amplitude and time-course between the groups. The differential effect of conditioning and pseudoconditioning on the evoked response and changes in temperature eliminate the possibility that effects of stress, arousal and muscular effort are the primary cause of the changes in the EPSP. The results suggest that behavioural events can exert bidirectional control of synaptic strength of entorhinal cortex inputs to the dentate gyrus and that the sign of synaptic modification is at least in part determined by the temporal relationship between these events. The data are discussed in terms of the type of neural activity that may mediate the processing of information in the dentate gyrus.

Animals↗
PubMed1997

Enhancement of an inhibitory input to the feeding central pattern generator in Lymnaea stagnalis during conditioned taste-aversion learning.

To study the neuronal mechanism of a conditioned taste-aversion (CTA) learning in the pond snail Lymnaea stagnalis, we examined the synaptic connection between the neuron 1 medial (N1M) cell and the cerebral giant cell (CGC), the former is an interneuron in central pattern generator for the feeding response and the latter is a regulatory neuron to the central pattern generator. Inhibitory postsynaptic potential (IPSP) which was evoked in the N1M cell by activation of the CGC was larger and lasted longer in the conditioned animal than that in the control animal. The electrical properties of the cell body of CGC and the responses of the CGC to the chemosensory inputs were not changed during the CTA learning. These results, together with the previous report indicating the existence of excitatory projection from the N1M cell to the feeding motoneuron, suggest that enhanced IPSP in the N1M cell may underlie the suppression of feeding responses in the Lymnaea CTA learning.

Animals↗
PubMed1984

The effects of trimethyltin chloride on the acquisition of long delay conditioned taste aversion learning in the rat.

Naive rats injected with LiCl at various times following consumption of a novel saccharin solution subsequently avoided the ingestion of saccharin with the degree of the aversion related to the interval between ingestion and LiCl administration. Although a similar relationship was also evident in animals which had received a single intragastric administration of trimethyltin chloride 21 days prior to the pairing of saccharin and LiCl, the trimethyltin-pretreated subjects receiving delayed injections of LiCl displayed weaker taste aversions than those not exposed to trimethyltin. This disruption in the acquisition of taste aversions over long delays is consistent with other work suggesting that trimethyltin disrupts tasks involving short-term memory. The utility of the conditioned taste aversion paradigm in detecting and characterizing drug toxicity was discussed.

Animals↗
PubMed2005

Lesions of orbitofrontal cortex impair rats' differential outcome expectancy learning but not conditioned stimulus-potentiated feeding.

Patients with damage to the orbitofrontal cortex (OFC) display various impairments in cognitive and affective function, including a reduced ability to use information about the consequences of their actions to guide their behavior. In this study, rats with neurotoxic lesions of the OFC failed to use specific expectancies about outcomes to guide their learning of an instrumental discrimination task. In contrast, lesioned rats were unimpaired in a measure of learned motivational function, the potentiation of feeding under conditions of food satiation, by a conditioned stimulus that had been paired with food while the rats were food deprived. Notably, performance of both of these tasks has been shown to depend on the function of the basolateral amygdala (BLA), a region that is richly interconnected with the OFC. Thus, the present results are consistent with the view that the acquisition and use of specific outcome expectancies to guide behavior critically involve a neural system that includes the BLA and the OFC, but they indicate that certain motivational properties acquired by cues on the basis of appetitive learning involve BLA circuitry apart from the OFC.

Animals↗
PubMed1985

Motor learning in rats: modification of the pattern of reaching and licking by operant conditioning.

Motor learning was studied in computer controlled experiments in which the prolongation of a definite phase of a discrete movement was reinforced by intracranial selfstimulation or by the offer of water. In Experiment 1, rats slowed down the retraction phase of the lateralized reaching reaction from 300 ms to 512 ms. In Experiment 2, rats learned to follow computer generated spout movement by increasing the interlick interval or by alternating long and short licks.

Animals↗
PubMed1991

Locus coeruleus involvement in the learning of classically conditioned bradycardia.

Opioid agonists are known to inhibit the activity of locus coeruleus (LC) neurons. In this study, microinjections of the mu-opioid agonist [D-Ala2, N-Me-Phe4, Gly5-ol]-enkephalin (DAMGO; 1.6 microM) bilaterally into the LC caused a significant impairment in the development of a heart-rate (HR) conditioned response (CR). The adverse effect of DAMGO on the HR CR could be reversed with naltrexone pretreatment. Microinjections of DAMGO into the periaqueductal gray, parabrachial nucleus, or fourth ventricle structures 1-2 mm away from the LC had no effects on the development of an HR CR. We conclude that central noradrenergic activity as mediated by the LC is critically involved in the learning and retention of conditioned cardiovascular responses.

Analysis of Variance↗
PubMed2002

Role of the nuclei in eyeblink conditioning.

Evidence to date supports the strong conclusion that the cerebellum learns. Classical conditioning of the eyeblink response is critically dependent upon the cerebellum. The issue addressed here is whether cerebellar cortex or deep nuclei form the basic association. Learning occurs with large cerebellar cortical aspirations in rabbits and with a Purkinje-cell-deficient mutation in mice. The learned response is poorly timed, small in amplitude, and inconsistent in its occurrence. Learning nevertheless occurs. Lesions of the interpositus, on the other hand, prevent new learning and abolish previously learned conditioned responses. Small electrolytic lesions, kainic acid lesions, and temporary inactivation (cooling, muscimol, anisomycin) localize learning to the dorsolateral anterior interpositus nucleus. Learning-related unit activity-the signature of the engram-recorded throughout the brain depends on the interpositus. Electrical stimulation of interpositus afferents are needed for conditioning, and the conditioned interpositus has a lowered threshold. Finally, a recent anatomical study with electron microscopy shows synaptic changes in the excitatory inputs to the interpositus with conditioning. The interpositus is responsible for making the basic association between conditioned and unconditioned stimuli, which in turn allows ancillary learning to occur in cerebellar cortex, and possibly brainstem and forebrain.

Animals↗
PubMed2004

Odor of taste stimuli in conditioned "taste" aversion learning.

The present research addresses whether rats can express odor aversions to the odor of taste stimuli. In Experiment 1, saccharin or salt were either mixed in distilled water, so the rats could taste and smell them, or presented on disks attached to the tubes' metal spouts so the rats could only smell them. Aversions were established to taste stimuli under both conditions. The results of Experiment 2 indicate that conditioning was to the odor of the tastes when they were presented on disks in Experiment 1, hence both taste and odor aversions were established by means of "taste" stimuli. Taste aversion learning thus may more properly be termed flavor aversion learning, with flavor referring to both taste and odor components.

Animals↗
PubMed2006

Dopamine activity in the nucleus accumbens modulates blocking in fear conditioning.

Associative learning depends on the discrepancy between actual and predicted outcomes. The neurochemical mechanisms involved in regulating this discrepancy in Pavlovian fear conditioning in rats are unknown. We employed the blocking paradigm to show that this learning discrepancy is decreased by heightened activation of dopamine following an accumbal infusion of d-amphetamine, and increased by dopaminegic blockade following an accumbal infusion of cis-(z)-flupenthixol or by combined infusions of the D1 (SCH23390) and D2 (sulpiride) antagonists but not by infusion of either alone.

Animals↗