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Results for “Contrastive learning”

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At least 127 records · Page 7Linked to original sources

PubMed1994

Differential effects of serotonin and raphe grafts in the hippocampus and hypothalamus: a combined behavioural and anatomical study in the rat.

Combined with a partial cholinergic deficiency, serotonergic lesions induce severe spatial learning deficits. Serotonergic lesions, however, have additional effects, such as reduced body weight and disruption of thermoregulation, which may be the cause of the observed learning deficits. Restoration of the serotonergic innervation of the hippocampus by raphe grafts reduces these learning deficits. The effects of the grafts may result from a direct support of spatial learning but may also be an indirect result of preventing some of the other effects of serotonergic lesions. In the present study we used raphe grafts to examine the selectivity and specificity of the effects of serotonergic lesions in the rat, and used the behavioural effects as an indication of successful transplantation in order to examine the fine details of such grafts. Raphe grafts in the hippocampus did not prevent the effects of the lesions on body weight, thermoregulation and exploratory behaviour but did minimize the effects of the lesions on spatial learning. In contrast, raphe grafts in the hypothalamus reduced the effects of the lesions on thermoregulation but failed to support learning. The grafted fibres showed termination specificity with the interneurons, which is typical of the serotonergic innervation of the normal hippocampus. The results indicate that the serotonergic innervation of the hippocampus functions locally to support spatial learning. This role of serotonin is independent of its involvement in modulation of body weight, thermoregulation or exploratory behaviour. The results confirm that the modes of serotonergic action in the hippocampus include the selective innervation of specific interneuron subpopulations.

5,7-Dihydroxytryptamine↗

PubMed2002

Morphine conditioned reward is inhibited by MPEP, the mGluR5 antagonist.

In the present study we examined the effect of MPEP [2-methyl-6-(phenylethynyl)-pyridine] a potent, selective and systemically active metabotropic glutamate receptor (mGluR) type I (subtype mGluR5) antagonist on conditioned morphine reward in mice. In an unbiased version of conditioned place preference (CPP) paradigm, single conditioning with 10 mg/kg of morphine produced reliable place preference. MPEP at 30, but not 10 mg/kg significantly inhibited the acquisition as well as expression of morphine-induced CPP, but it neither produced place preference or aversion, nor affected locomotor activity of mice. Effects of MPEP on learning and memory were studied in the elevated plus maze model of spatial learning. In contrast to 0.1 mg/kg of MK-801, which inhibited the acquisition of this task, 30 mg/kg of MPEP affected neither learning nor memory retrieval. These data suggest that mGluR5 may be involved in conditioned morphine reward.

Animals↗

PubMed1999

Ibotenic acid lesions of the basolateral, but not the central, amygdala interfere with conditioned taste aversion: evidence from a combined behavioral and anatomical tract-tracing investigation.

Rats (Rattus norvegicus) with almost complete ibotenic acid lesions (at least 90%) of the basolateral amygdaloid complex (BLA) failed to learn a conditioned taste aversion (CTA; Experiment 1A). In these same BLA rats, the bidirectional parabrachial-insular pathway that courses through the central nucleus of the amygdala (Ce) was shown to be spared (Experiment 1B), indicating that the BLA per se is critical for CTA learning. In contrast to the deleterious effect of BLA lesions on CTA, ibotenic acid lesions of the Ce did not block CTA learning (Experiment 2). Nonreinforced preexposure to the gustatory stimulus attenuated CTA acquisition in normal rats, and, under these conditions, rats with BLA lesions were no longer impaired (Experiment 3). Thus, ibotenic acid lesions centered over the Ce, sparing a considerable extent of the BLA, together with the testing procedure used in previous experiments (e.g., L. T. Dunn & B. J. Everitt, 1988), led to the belief that the CTA deficits reported after electrolytic lesions of the amygdala were the result of incidental damage to fibers of passage.

Amygdala↗

PubMed2005

The interaction of the explicit and the implicit in skill learning: a dual-process approach.

This article explicates the interaction between implicit and explicit processes in skill learning, in contrast to the tendency of researchers to study each type in isolation. It highlights various effects of the interaction on learning (including synergy effects). The authors argue for an integrated model of skill learning that takes into account both implicit and explicit processes. Moreover, they argue for a bottom-up approach (first learning implicit knowledge and then explicit knowledge) in the integrated model. A variety of qualitative data can be accounted for by the approach. A computational model, CLARION, is then used to simulate a range of quantitative data. The results demonstrate the plausibility of the model, which provides a new perspective on skill learning.

Cognition↗

PubMed2004

Modulation of learning and memory in Dahl rats by dietary salt restriction.

The Dahl rat represents a robust animal model of salt-sensitive hypertension, with Dahl S rats being salt sensitive and Dahl R rats (the Dahl S counterparts) being salt resistant for the development of hypertension. Here we evaluate the effect of reduced dietary salt intake on learning and memory in the Dahl rat model. Salt restriction produced a significant impairment in social transmission of food preference and social recognition memory in Dahl S rats without affecting spatial learning. In contrast, social transmission of food preference and social recognition memory remained unaffected in Dahl R rats, whereas navigation performance was significantly improved. This effect on learning and memory was not generalized because sodium restriction did not influence object recognition memory in either Dahl S or Dahl R rats. The significant decrement in select cognitive functions in Dahl S rats produced by salt restriction are in sharp contrast to the well known positive effect of dietary salt restriction in alleviating high blood pressure and associated target organ complications, suggesting that caution must be exercised when weighing the benefits of salt restriction in improving cardiovascular health in salt-sensitive hypertension against the potential undesirable effects of reduced cognitive function.

Animals↗

PubMed1994

Flumazenil antagonizes the effect of diazepam on negative contrast in one-way avoidance learning.

The main aim of the present work was to study whether the effect of diazepam upon successive negative contrast in one-way avoidance learning-induced by shifting rats from a large reward (30s spent in the safe compartment) to a small reward (1s)-is mediated by the action of this drug on the benzodiazepine (BZ) receptor. Therefore, we studied the influence of flumazenil (FL), a BZ antagonist, on the effect of diazepam (DZ) on negative contrast. The i.p. administration of 5 and 12mg/kg, but not of 2mg/kg of FL, reliably antagonized the abolition by DZ (1mg/kg) on successive negative contrast. Moreover, FL (12mg/kg) did not affect either the avoidance response or the contrast effect. These results suggest that the GABA system is involved in the successive negative contrast effect in one-way avoidance learning, and that this experimental procedure may be useful in studies of anti-anxiety agents.

Journal Article↗

PubMed1990

Sparing of attentional relative to mnemonic function in a subgroup of patients with dementia of the Alzheimer type.

Patients with dementia of the Alzheimer type (DAT) received two tests of visual selective attention, together with tests of spatial and visual recognition memory and visuospatial conditional learning previously used to show deficits early in the course of DAT. One set of attentional tests compared visual discrimination learning along intra- and extra-dimensional shifts, using a "total change" design. In the 12 DAT patients capable of attempting the extra-dimensional shift (subgroup 1), performance was equivalent to that of controls. This subgroup was also unimpaired at simple and compound discrimination learning and reversal and an intra-dimensional shift. They were as accurate as controls on a visual search task requiring matching of stimuli on two dimensions with variable numbers of alternatives, but were significantly impaired in the tests of recognition memory and learning. By contrast, the other 13 patients showed marked impairments in the attentional tasks. This subgroup was also significantly worse than subgroup 1 in performance on the visual recognition and conditional learning tasks, and showed greater severity on most of the clinical ratings of dementia. The sparing of attentional shifting in patients early in the course of DAT is contrasted with the impairments previously described in patients with Parkinson's disease with only mild or absent memory loss. The implications of this double dissociation of deficits for understanding the neural bases of the cognitive deficits in these two neurodegenerative diseases are discussed and their significance for the staging of DAT is considered.

Aged↗

PubMed2003

Procedural learning in schizophrenia after 6 months of double-blind treatment with olanzapine, risperidone, and haloperidol.

RATIONALE: First generation antipsychotics induce extrapyramidal motor symptoms (EPS), presumably through dopamine D(2) receptor blockade at the dorsal striatum. This may also produce impairment of cognitive processes, such as procedural learning, that are dependent on this region. Haloperidol and, to a lesser extent, risperidone, are active in the dorsal striatum and may induce EPS and impairment of procedural learning. In contrast, the prototypical second-generation antipsychotic, clozapine, is less active in the dorsal striatum and does not induce EPS or impair procedural learning. Olanzapine is pharmacologically similar to clozapine and has a low incidence of EPS induction. OBJECTIVES: To assess the hypothesis that olanzapine would not have a deleterious effect on procedural learning. METHODS: Thirty-nine subjects with early phase schizophrenia were randomly assigned to double blind treatment with haloperidol, risperidone, or olanzapine. They were administered the Tower of Toronto test at an unmedicated baseline and again following 6 weeks and 6 months of treatment. RESULTS: Procedural learning, defined as the improvement observed between two blocks of five trials of the Tower of Toronto, was preserved after 6 weeks of all three treatments but showed a substantial decline after 6 months of treatment with haloperidol or risperidone. CONCLUSIONS: These data are consistent with the differential activity of the three medications in dorsal striatum structures and suggest that the advantages of olanzapine over haloperidol and risperidone in relation to extrapyramidal syndromes may also generalize to procedural learning. The results also suggest that the procedural learning disadvantages of haloperidol and risperidone accrue slowly but are apparent after 6 months of treatment.

Adolescent↗

PubMed1997

Uncompetitive NMDA receptor antagonists attenuate NMDA-induced impairment of passive avoidance learning and LTP.

In general, N-methyl-D-aspartate (NMDA) receptor antagonists inhibit learning and long term potentiation (LTP). However, it has been suggested that direct tonic, i.e. non-temporal, activation of NMDA receptors, in contrast to learning, may lead to an increase in synaptic "noise" and, in turn, to a loss of association detection. In the present study, a two-choice passive avoidance task and LTP in vitro (CA1 hippocampal region) were used to address this issue. Dark avoidance learning was impaired by systemic NMDA administration (starting at 25 mg/kg) that was not related to either toxic effects or state-dependent learning. NMDA-induced amnesia was antagonized by ((+)-5-methyl-10,11-dihydro-5H-dibenzocyclohepten-5,10-imine maleate (MK-801) and 1-amino-3,5-dimethyladamantane (memantine), starting at low doses of 0.05 and 2.5 mg/kg, respectively, in a bell-shaped dose-response relationship. A competitive NMDA receptor antagonist CGP-39551 failed to reverse NMDA-induced amnesia. In hippocampal slices, NMDA (10 microM) depressed (S)-alpha-amino-3-hydroxy-5-methyl-4-isoxazolproprionic acid (AMPA) receptor-mediated field potentials in CA1 and also caused a moderate reduction of LTP induction/expression. It was this latter effect that was antagonized by memantine (1 microM). Thus, under conditions of tonic activation of NMDA receptors, uncompetitive NMDA receptor antagonists can paradoxically reverse deficits in learning and synaptic plasticity.

2-Amino-5-phosphonovalerate↗

PubMed2005

Learning to produce predicted static handgrip forces.

The objective of this study was to prove the hypothesis that kinaesthetic sensations, without visual or verbal guidance, give sufficient information to produce predictive handgrip forces. The ability of 70 girls and 70 boys aged 11 to 17 years to produce predicted static handgrip force was examined. The subjects were requested to produce 50% of their individual maximum handgrip force and maintain it for 2 seconds without visual control. Ten trials were done first by the right-hand and then by the left-hand. The maximum grip strength increased parallel with age, but significant differences were found between both the right and the left-hand, and the genders. Close correlations were found between the desired and the exerted forces. The differences between the desired forces and the exerted forces produced by the fifth trials were significantly smaller than that of the first trials. The verbal information about each exerted force contributed to the learning with right-hand since it caused a further decrease in the difference between the desired force and the exerted force. In contrast, the learning with left-hand was not enhanced by verbal feedback. These results suggest that kinaesthetic feedback information from the hand plays an effective role in learning to produce predicted grip strengths without visual and verbal information.

Adolescent↗

PubMed1996

Place learning and hippocampal synaptic plasticity in streptozotocin-induced diabetic rats.

Moderate impairment of learning and memory has been recognized as a complication of diabetes. The present study examined behavioral and electrophysiological measures of cerebral function in streptozotocin (STZ)-induced diabetic rats. Behavioral testing consisted of a spatial learning task in a water maze. Electrophysiological testing consisted of in vitro assessment of hippocampal long-term potentiation (LTP), an activity-dependent form of synaptic plasticity, which is believed to be related to the cellular mechanisms of learning and memory. Two experiments were performed: the first with severely hyperglycemic rats and the second with moderately hyperglycemic rats. Rats were tested in the water maze 11 weeks after induction of diabetes. Next, LTP was measured in vitro in trained animals. Both spatial learning and LTP expression in the CA1 field of the hippocampus were impaired in severely hyperglycemic rats as compared with nondiabetic controls. In contrast, spatial learning and hippocampal LTP were unaffected in moderately hyperglycemic rats. The association of alterations in hippocampal LTP with specific learning impairments has previously been reported in conditions other than diabetes. Our findings suggest that changes in LTP-like forms of synaptic plasticity in the hippocampus, and possibly in other cerebral structures, are involved in learning deficits in STZ-induced diabetes. The beneficial effect of moderate glycemic control on both place learning and hippocampal LTP supports the significance of the relation between these two parameters and indicates that the development of the observed deficits may be related to the level of glycemic control.

Animals↗

PubMed2004

Clinical governance and the learning organization.

AIM: This paper compares and contrasts clinical governance and organizational learning. BACKGROUND: Clinical governance represents one of the most significant policy developments in recent years. It places on all health care delivery organizations a statutory duty to develop the systems, standards and processes necessary to improve health care quality and manage risk. At the same time, many health care organizations are seeking new ways in which learning can be retained and deployed more widely within the organization (organizational learning). KEY ISSUES: Both approaches emphasize cultural changes as essential underpinnings to quality improvement. However, the two approaches also differ fundamentally in their logic of action. Clinical governance is essentially 'top down', being built around formal standards, established procedures, and regular monitoring and reporting. In contrast, organizational learning emphasizes 'bottom up' changes in values, beliefs and motivations in such a way that learning and change are prioritized. The challenge for managers and practitioners lies in seeking a creative tension between these two contrasting styles of organizational change.

Attitude of Health Personnel↗

PubMed2002

Involvement of mu(1)-opioid receptors and cholinergic neurotransmission in the endomorphins-induced impairment of passive avoidance learning in mice.

The effects of naloxonazine, a mu(1)-opioid receptor antagonist, and physostigmine, a cholinesterase inhibitor, on the endomorphins-induced impairment of passive avoidance learning were investigated in mice. Endomorphin-1 (10 microg) and endomorphin-2 (10 microg) significantly impaired passive avoidance learning, while naloxonazine (35 mg/kg, s.c.), a mu(1)-opioid receptor antagonist, which alone failed to influence passive avoidance learning significantly inhibited the endomorphin-1 (10 microg)- but not endomorphin-2 (10 microg)-induced disturbance of such learning. A rather nonselective higher dose (50 mg/kg, s.c.) of naloxonazine almost completely antagonized the endomorphin-1 (10 microg)- and endomorphin-2 (10 microg)-induced impairment of passive avoidance learning. In contrast, physostigmine (0.025 and 0.05 mg/kg, i.p.) significantly reversed the endomorphin-1 (10 microg)- and endomorphin-2 (10 microg)-induced disturbance of passive avoidance learning, whereas physostigmine (0.025 and 0.05 mg/kg, i.p.) alone did not influence such learning. These results suggest that endomorphin-1 but not endomorphin-2 impairs learning and memory resulting from cholinergic dysfunction, and from activation of mu(1)-opioid receptors.

Animals↗

PubMedDate not supplied

[Comparative characteristics of the action of sydnocarb, phenamine and caffeine on multiple alteration in the orientation of the avoidance response in rats].

The ability of rats to alter orientation of the avoidance response in an Y-shaped maze was determined. Sydnocarb (20 mg/kg) improved the reversal learning of the animals, shortened the latent reaction periods and did not upset passive avoidance. Amphetamine (0.5 mg/kg) and caffein (25 mg/kg) shortened the latency of reactions, but did not affect the reversal learning. In large doses (2 and 5 mg/kg) amphetamine distinctly disturbed the reversal learning, while sydnocarb (50 mg/kg) did not impair the alteration of the avoidance response. In rats poorly amenable to reversal learning during control testing syndnocarb facilitated the alteration of the habit better than other drugs. In animals well amenable to reversal learning, in contrast to amphetamine and caffein, it did not derange their behavior.

Amphetamine↗

PubMed2001

The nature of declarative and nondeclarative knowledge for implicit and explicit learning.

Using traditional implicit and explicit artificial-grammar learning tasks, the author investigated the similarities and differences between the acquisition of declarative knowledge under implicit and explicit learning conditions and the functions of the declarative knowledge during testing. Results suggested that declarative knowledge was not predictive of or required for implicit learning but was related to consistency in implicit learning performance. In contrast, declarative knowledge was predictive of and required for explicit learning and was related to consistency in performance. For explicit learning, the declarative knowledge functioned as a guide for other behavior. In contrast, for implicit learning, the declarative knowledge did not serve as a guide for behavior but was instead a post hoc description of the most commonly seen stimuli.

Adult↗

PubMed2006

Easier done than undone: asymmetry in the malleability of implicit preferences.

Dual-process models imply that automatic attitudes should be less flexible than their self-reported counterparts; the relevant empirical record, however, is mixed. To advance the debate, the authors conducted 4 experiments investigating how readily automatic preferences for one imagined social group over another could be induced or reversed. Experiments 1 and 2 revealed that automatic preferences, like self-reported ones, could be readily induced by both abstract supposition and concrete learning. In contrast, Experiments 3 and 4 revealed that newly formed automatic preferences, unlike self-reported ones, could not be readily reversed by either abstract supposition or concrete learning. Thus, the relative inflexibility of implicit attitudes appears to entail, not immunity to sophisticated cognition, nor resistance to swift formation, but insensitivity to modification once formed.

Attitude↗

PubMed1985

Cerebral glucose metabolism in aging rodents: effects of co-dergocrine.

Because glucose is the primary substrate for oxidative metabolism of the adult brain, measurements of glucose utilization provide information on cerebral energy metabolism, which ultimately is linked to neuronal activity. Early studies utilized in vitro techniques to measure carbohydrate oxidation as well as glycolytic and citric acid cycle enzymatic activities as a function of age. Although the results of these studies are somewhat equivocal, they generally indicate a decline in cerebral carbohydrate metabolism in senescent rodents. More recently, local cerebral glucose utilization (LCGU) has been measured in awake, resting rats with the 2-deoxy-D[1-14C]glucose metabolic mapping technique. Using this technique, decrements in LCGU have been observed in rats by midlife. Co-dergocrine, an ergot alkaloid used extensively in geriatric psychopharmacology, reversed subcortical LCGU decrements in brain areas associated with motor function, motivation, and learning. In contrast, the drug decreased frontal cortical LCGU in middle-aged rats. Stimulatory effects of co-dergocrine on LCGU in brain areas associated with motivation and learning support the view that the drug may be useful against age-associated disorders of cognition. Furthermore, the co-dergocrine-induced decrease in cortical glucose utilization coupled with the drug's cerebral vasoconstrictive action may render cortical cells less susceptible to the sequelae of ischemia.

Aging↗

PubMed2000

Facilitatory effect of ritanserin is mediated by dopamine D(1) receptors on olfactory learning in young rats.

The olfactory bulb is critically involved in early olfactory learning. In this study, we examined the effect of intrabulbar infusion of ritanserin, a 5-hydroxytryptamine(2) (5-HT(2)) receptor antagonist on a one-trial aversive olfactory learning in young rats. Ritanserin, a 5-HT(2) receptor antagonist, was continuously infused into the olfactory bulb of postnatal day-11 (PND 11) rat pups during a 30-min training session of pairing citral odor and foot shock. On the following day, the time spent in the part of the apparatus where the odor was present was measured as an index of odor aversion. Consistent with a previous study on olfactory preference learning, 1 nM ritanserin, but not 10 nM, blocked the olfactory aversive learning. We further examined the ability of 10 nM ritanserin to induce olfactory learning in the absence of the unconditioned stimulus foot shock. Pups that received intrabulbar infusion of 10 nM ritanserin in the presence of citral odor developed an aversion to the odor without foot shock. Since ritanserin has been shown to have an affinity for dopamine receptors, we examined the effect of dopamine antagonists on the ritanserin-induced aversive olfactory learning. Co-infusion of the dopamine D(1) receptor antagonist (+/-)-SKF-83566 with ritanserin dose-dependently prevented induced learning. In contrast, the D(2) receptor antagonist spiperone was without effect. These results extend the previous finding on the role of bulbar 5-HT(2) receptors in early olfactory learning and suggest that high concentration of ritanserin facilitates aversive olfactory learning through D(1) receptors in the olfactory bulb.

Animals↗