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At least 271 records · Page 15Linked to original sources
PubMed2003

GABA neurotransmission in the cerebellar interposed nuclei: involvement in classically conditioned eyeblinks and neuronal activity.

The cerebellar interposed nuclei (IN) are an essential part of circuits that control classically conditioned eyeblinks in the rabbit. The function of the IN is under the control of GABAergic projections from Purkinje cells of the cerebellar cortex. The exact involvement of cerebellar cortical input into the IN during eyeblink expression is not clear. While it is known that the application of gamma-aminobutyric acid-A (GABA(A)) agonists and antagonists affects the performance of classically conditioned eyeblinks, the effects of these drugs on IN neurons in vivo are not known. The purpose of the present study was to measure the effects of muscimol and picrotoxin on the expression of conditioned eyeblinks and the activity of IN cells simultaneously. Injections of muscimol abolished conditioned responses and either silenced or diminished the activity of IN cells. Two injections were administered in each picrotoxin experiment. The first injection of picrotoxin slightly modified the timing and amplitude of the eyeblink, produced mild tonic eyelid closure, increased tonic activity of IN cells, and reduced the amplitude of the neural responses. The second injection of picrotoxin abolished conditioned responses, further increased tonic eyelid closure, dramatically elevated the tonic activity of IN cells, and in most cases, abolished neuronal responses. These results demonstrate that both GABA(A)-mediated inactivation and tonic up-regulation of IN cells can interrupt the expression of conditioned eyeblinks and that this behavioral effect is accompanied by the suppression of the neuronal activity correlates of the conditioned stimulus and response.

Animals↗
PubMed1992

Stress-induced facilitation of classical conditioning.

Stress has been shown to impair subsequent learning. To determine whether stress would impair classical conditioning, rats were exposed to inescapable, low-intensity tail shock and subsequently classically conditioned under freely moving conditions with a brief periorbital shock unconditioned stimulus and a white noise conditioned stimulus. Unexpectedly stressed rats exhibited significantly more conditioned eyeblink responses and the magnitude of their individual responses was also enhanced. These results stand in contrast to the learning deficits typically observed and suggest that stress can enhance the acquisition of discrete conditioned responses.

Acoustic Stimulation↗
PubMed1997

Dendritic excitability microzones and occluded long-term depression after classical conditioning of the rabbit's nictitating membrane response.

We made intradendritic recordings in Purkinje cells (n = 164) from parasaggital slices of cerebellar lobule HVI obtained from rabbits given paired presentations of tone and periorbital electrical stimulation (classical conditioning, n = 27) or explicitly unpaired presentations of tone and periorbital stimulation (control, n = 16). Purkinje cell dendritic membrane excitability, assessed by the current required to elicit local dendritic calcium spikes, increased significantly in slices from animals that received classical conditioning. In contrast, membrane potential, input resistance, and amplitude of somatic and dendritic spikes were not different in slices from animals given paired or explicitly unpaired stimulus presentations. The location of cells with low thresholds for local dendritic calcium spikes suggested that there are specific sites for learning-related changes within lobule HVI. These areas may correspond to learning "microzones" and are consistent with locations of learning-related in vivo changes in Purkinje cell activity. Application of 4-aminopyridine, an antagonist of the rapidly inactivating potassium current IA, reduced the threshold for dendritic spikes in slices from naive animals to levels found in slices from trained animals. In cells where thresholds for eliciting parallel fiber-stimulated Purkinje cell excitatory postsynaptic potentials (EPSPs) were measured, levels of parallel fiber stimulation required to elicit a 6-mV EPSP as well as a 4-mV EPSP (n = 30) and a Purkinje cell spike (n = 56) were found to be significantly lower in slices from paired animals than unpaired controls. A classical conditioning procedure was simulated in slices of lobule HVI by pairing a brief, high-frequency train of parallel fiber stimulation (8 pulses, 100 Hz) with a brief, lower frequency train of climbing fiber stimulation (3 pulses, 20 Hz) to the same Purkinje cell. Following paired stimulation of the parallel and climbing fibers, Purkinje cell EPSPs underwent a long-term (> 20 min) reduction in peak amplitude (-24%) in cells (n = 12) from animals given unpaired stimulus presentations but to a far less extent (-9%) in cells (n = 20) from animals given in vivo paired training. Whereas 92% of cells from unpaired animals showed pairing-specific depression, 50% of cells from paired animals showed no depression and in several cases showed potentiation. Our data establish that there are localized learning-specific changes in membrane and synaptic excitability of Purkinje cells in rabbit lobule HVI that can be detected in slices 24 h after classical conditioning. Long-term changes within Purkinje cells that effect this enhanced excitability may occlude pairing-specific long-term depression.

Animals↗
PubMed1995

Brain mechanisms in human classical conditioning: a PET blood flow study.

Five healthy male subjects participated in a classical conditioning experiment, and positron emission tomography (PET) was used to compare regional cerebral blood flow before and after conditioning. The subjects participated in three different experimental phases. In the first (habituation) phase they listened to 24 repetitions of a tone with random intervals. In the second (acquisition) phase, the tone was paired with a brief shock to the wrist. In the third (extinction) phase, the tone was presented alone again. 15OPET scans were taken during the habituation and extinction phases. Because the habituation and extinction phases were similar, any difference in blood flow to the tones presented during extinction probably reflected conditioning that occurred during the acquisition phase. Statistical parametric mapping (SPM) analysis of the PET data showed significantly increased activation in the right hemisphere in the orbito-frontal cortex, dorsolateral prefrontal cortex, inferior and superior frontal cortices, and inferior and middle temporal corticies. The only activated areas in the left hemisphere were area 19 and the superior frontal cortex. The results are interpreted as evidence for the involvement of cortical areas in human classical conditioning.

Acoustic Stimulation↗
PubMed1991

Classical conditioning selectively increases AMPA receptor binding in rabbit hippocampus.

The NMDA and AMPA receptors have been shown to play critical roles in various forms of synaptic plasticity (learning and memory, long-term potentiation). The present study investigated the involvement of these two receptors in a well-characterized classical conditioning paradigm. Following classical conditioning of the rabbit nictitating membrane the binding properties of these two subclasses of excitatory amino acid transmitter receptors were analyzed in dorsal hippocampi by quantitative autoradiography. [3H] TCP and [3H] AMPA were used to identify the NMDA and AMPA receptors, respectively. The binding of [3H]TCP to the NMDA receptor remained unchanged in all the experimental groups tested. Paired presentations of the conditioned and unconditioned stimuli resulted in increased [3H] AMPA binding to the AMPA receptor in several subfields of the hippocampus, while unpaired presentations had no significant effects. The increase in binding was due to an increased affinity of the low-affinity component of the AMPA receptor. The results support the hypothesis that changes in glutamate receptors participate in the synaptic plasticity involved in certain forms of learning.

Animals↗
PubMed1998

Trace eyeblink classical conditioning in the monkey: a nonsurgical method and behavioral analysis.

Classical eyeblink conditioning has been used extensively to study the neurobiology of associative learning and memory in rabbits and in humans. During the last several years, new developments have renewed interest in the possibility of studying classical conditioning in monkeys. Specifically, it is now known that impaired conditioning can be observed in humans with various neurologic problems, including amnesia, and thus there is now considerable interest in the neurobiology of human eyeblink conditioning. Research involving monkeys, in which discrete lesions of anatomically defined neural structures can be produced, has the potential to provide information that might not be readily available from work in humans. Here, the authors present a simple, nonsurgical method for classically conditioning the eyeblink response in monkeys and report behavioral results using a trace conditioning paradigm that is sensitive to hippocampal damage in both rabbits and humans. This method is reliable and effective for recording eyeblinks and shows that robust eyeblink classical conditioning can be readily established in the monkey.

Analysis of Variance↗
PubMed2001

In vitro eye-blink classical conditioning is NMDA receptor dependent and involves redistribution of AMPA receptor subunit GluR4.

The classically conditioned vertebrate eye-blink response is a model in which to study neuronal mechanisms of learning and memory. A neural correlate of this response recorded in the abducens nerve can be conditioned entirely in vitro using an isolated brainstem-cerebellum preparation from the turtle by pairing trigeminal and auditory nerve stimulation. Here it is reported that conditioning requires that the paired stimuli occur within a narrow temporal window of <100 msec and that it is blocked by the NMDA receptor antagonist d,l-2-amino-5-phosphonovaleric acid. Moreover, there is a significant positive correlation between the levels of conditioning and greater immunoreactivity with the glutamate receptor 4 (GluR4) AMPA receptor subunit in the abducens motor nuclei, but not with NMDAR1 or GluR1. It is concluded that in vitro classical conditioning of an abducens nerve eye-blink response is generated by NMDA receptor-mediated mechanisms that may act to modify the AMPA receptor by increasing GluR4 subunits in auditory nerve synapses.

Abducens Nerve↗
PubMed1988

The effect of lesions of cerebellar cortex on retention of the classically conditioned eyeblink response when stimulation of the lateral reticular nucleus is used as the conditioned stimulus.

Ten male albino rabbits were implanted with stimulating electrodes in the lateral reticular nucleus (LRN). These rabbits were given paired classical conditioning training of the nictitating membrane response with stimulation of the LRN as the conditioned stimulus (CS) Each rabbit was given daily training sessions until it consistently made conditioned responses (CRs). Each rabbit then received an aspiration lesion of cerebellar cortex; the ipsilateral anso-paramedian lobule (n = 6), the anterior or central vermis (n = 2), the central vermis and ansiform lobule (n = 1), or the central vermis and paramedian lobule (n = 1). After recovery, these rabbits were again given paired classical conditioning training with LRN stimulation as the CS. The rabbits with anso-paramedian lesions did not retain the CR after the lesion, but were able to relearn it. The rabbits with lesions of the vermis, the vermis and ansiform, or the vermis and paramedian retained the CR after the lesion. These results are contrasted with previous results, which show that after aspiration of the anso-paramedian lobule, the conditioned response is not retained or relearned when stimulation of the dorsolateral pontine nucleus (DLPN) is used as a CS. The differences between the mossy fiber outputs of the LRN and DLPN may account for this discrepancy. Different regions of the cerebellum are apparently involved in retention of classically conditioned responses depending on the population of mossy fibers carrying the CS information.

Animals↗
PubMed1993

Delay classical conditioning in young and older rabbits: initial acquisition and retention at 12 and 18 months.

Classical conditioning of the nictitating membrane-eyeblink response in young (7 months old) and older (36 months old) New Zealand white rabbits in a delay paradigm with a 400-ms conditioned stimulus-unconditioned stimulus interval was examined for initial acquisition and retention. Older animals required significantly more acquisition trials to reach learning criterion. Age differences in acquisition were temporary. Older rabbits responded at a level comparable to that of young rabbits such that total performance over the 630 trials of acquisition was not different. Rabbits in the explicitly unpaired control groups exhibited no age differences in unconditioned response amplitude or latency measures. Twelve- and 18-month retests demonstrated no significant age effects on retention. Patterns of retention differed between the age groups. Older rabbits required fewer trials to obtain the learning criterion at each phase of testing. Younger rabbits maintained a stable performance throughout training.

Aging↗
PubMed1976

Neuronal substrate of classical conditioning in the hippocampus.

Neuronal activity in dorsal hippocampus was recorded in rabbits-during classical conditioning of nictitating membrane response, with tone as conditioned stimulus and corneal air puff as unconditioned stimulus. Unit activity in hippocampus rapidly forms a temporal neuronal "model" of the behavioral response early in training. This hippocampal response does not develop in control animals given unpaired stimuli.

Action Potentials↗
PubMed1967

Classical conditioning of courting behavior in the Japanese quail, Coturnix coturnix japonica.

Male Japanese quail were classically conditioned to display courting behavior at the sound of a buzzer, a previously neutral stimulus. The buzzer (conditioned stimulus) was paired with the presentation of a female quail (unconditioned stimulus) for a number of trials. The courting display, invariably elicited from the male by the presentation of the female, began to appear in part to the conditioned stimulus as early as the fifth pairing. All components of the display were elicited from all birds by the conditioned stimulus alone within 32 pairings of the conditioned and unconditioned stimuli.

Animals↗
PubMed1968

Successive reversals of a classically conditioned heart-rate discrimination.

Rats were trained to criterion in successive reversals of a classically conditioned heart-rate discrimination. Criterion was attained more rapidly in the later reversals in the series than in the early reversals and the inter-problem learning curve was of the same general form as that found with successive instrumental discrimination reversal in the same species.

Animals↗
PubMed1986

Effects of interstimulus interval and contingency on classical conditioning of the Aplysia siphon withdrawal reflex.

The siphon withdrawal reflex of Aplysia undergoes differential classical conditioning with cutaneous stimulation of the siphon or mantle shelf as the discriminative conditioned stimuli (CS+ and CS-) and shock to the tail as the unconditioned stimulus (US). The reflex has proved to be useful for analyzing the neural mechanisms of conditioning. To test the generality of this experimental system, we have begun to compare the properties of conditioning in Aplysia with those of conditioning in vertebrates. We first examined the effect of the interstimulus interval (ISI) by varying the time between presentation of the CS+ and the US in different groups of animals. Significant differential conditioning was obtained when the onset of the CS+ preceded the onset of the US by 0.5 sec, and marginal conditioning was obtained when the ISI was 1.0 sec. By contrast, no significant conditioning occurred when the CS+ preceded the US by 2, 5, or 10 sec, when the onsets of the stimuli were simultaneous, or when US onset preceded the CS+ by 0.5, 1.0, or 1.5 sec (backward conditioning). We next examined the effect of contingency by giving one group of animals normal differential conditioning, and a second group the same training but with additional USs inserted between the paired trials. Presentation of these additional USs reduced the degree to which the US was contingent on the CS+, but did not change the number of pairings. Animals receiving normal training again showed significant conditioning, whereas animals receiving additional USs showed no conditioning.(ABSTRACT TRUNCATED AT 250 WORDS)

Aplysia↗
PubMed1999

The effects of scopolamine on changes in regional cerebral blood flow during classical conditioning of the human eyeblink response.

We examined the effects of scopolamine on the functional anatomy of classical conditioning of the human eyeblink response. Ten healthy young normal female volunteers (mean age +/- SEM: 26.7 +/- 0.9 years) were administered 0.4 mg scopolamine intravenously 1 h before regional cerebral blood flow (rCBF) was measured with positron emission tomography (PET) and H215O. Scans occurred during three sequential phases: (1) explicitly unpaired presentations of the unconditioned stimulus (airpuff to the right eye) and conditioned stimulus (binaural tone), (2) paired presentations of the two stimuli (associative learning) and (3) explicitly unpaired presentation of the stimuli (extinction phase). Scopolamine impaired acquisition of the conditioned eyeblink response (54.7 +/- 4.9%) relative to 18 untreated subjects from two previous PET studies. Regions that showed significant relative increases in rCBF during conditioning included the right lateral occipital cortex, the right inferior occipital cortex, the right lateral temporo-occipital cortex, the left medial temporo-occipital cortex, the posterior cingulate, the right cerebellum/brain stem area and the medial cerebellum. Significant relative decreases in rCBF were measured in the thalamus, the left putamen/insula area, the right putamen and the left and middle cerebellar cortex. The data partially replicate previous findings in unmedicated young volunteers of conditioning-specific rCBF changes in the cingulate cortex, the cerebellar cortex, the insula and the lateral temporo-occipital cortex. Our finding of decreased rCBF in the thalamus and increased rCBF in the occipital cortex may be attributable to effects of scopolamine per se rather than conditioning. Our data lend further support to the notion that classical conditioning involves distributed changes in multiple systems within the central nervous system.

Acoustic Stimulation↗
PubMed1999

Classical conditions of environmental cues to cigarette smoking.

Smoking-related cues tend to produce urges and cardiac responses in smokers. This reactivity has been assumed to reflect prior classical conditioning. However, little direct evidence exists supporting the notion that environmental cues can be classically conditioned to cigarette smoking. In this study, 8 smokers received 22 daily trials during which 2 cue complexes (comprising visual, olfactory, and auditory stimuli) were paired with smoking (CS+ trials) and not smoking (CS- trials). Reactivity to the environmental cues, as measured by self-report of urge and pulse rate, increased across CS+ trials, diverging from responses in the CS- trials. Reactivity was stronger among light smokers and those who verbalized awareness of smoking contingencies. Findings indicate that environmental cues can be classically conditioned to smoking.

Adolescent↗
PubMed2000

Psychology of the scientist: LXXXII. Coverage of classical conditioning in textbooks in the psychology of learning, 1952-1995.

Objective information was obtained from 89 textbooks in the psychology of learning published from 1952 through 1995 to answer questions about their coverage of classical conditioning. We found (a) that classical conditioning consistently received less coverage than instrumental and operant conditioning, (b) that the distinction of classical and instrumental conditioning has become established as a textbook-construction device, (c) that use of the classical-instrumental distinction by textbook authors has "hardened" after a period of "fluidity" in the 1970s, (d) that the currency of references in the basic classical (as well as instrumental) conditioning chapters diminished from 1952 to 1995. Findings are discussed in regard to the possibility that, as a class, and in comparison to other textbooks, the textbooks of the psychology of learning fall short of fulfilling some of their recognized roles.

Animals↗
PubMed1980

Classical conditioning: induction of luteinizing hormone and testosterone secretion in anticipation of sexual activity.

A classical conditioning paradigm was used to demonstrate that male rats can learn to secrete luteinizing hormone and testosterone in anticipation of sexual activity. Sexually naïve males were exposed to a neutral stimulus and then to a sexually receptive female once daily. After exposure to the paired stimuli for 14 trials, the neutral stimulus was as effective as the female in triggering luteinizing hormone and testosterone secretion. These findings provide two novel perspectives on the control of reproductive hormone secretion in male rats: (i) environmental cues, which males learn to associate with sexual activity, induce the secretion of hormones that regulate pituitary-testis function, and (ii) classical conditioning may be used as a noninvasive method to evoke functional alterations in the secretion of luteinizing hormone and presumably the neuroendocrine pathways that mediate its release.

Animals↗