PubMed Health⌕ Search

SEARCH · PubMed Health

Results for “CONDITIONED LEARNING”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 487 records · Page 27Linked to original sources
PubMed2000

Time-dependent impairment of inhibitory avoidance retention in rats by posttraining infusion of a mitogen-activated protein kinase kinase inhibitor into cortical and limbic structures.

Mitogen-activated protein kinase (MAPK) is abundantly expressed in postmitotic neurons of the developed nervous system. MAPK is activated and required for induction of long-term potentiation (LTP) in the CA1 area of the hippocampus, which is blocked by the specific inhibitor of the MAPK kinase, PD 098059. Recently it was demonstrated that MAPK is activated in the hippocampus after training and is necessary for contextual fear conditioning learning. The present work tests the role of the MAPK cascade in step-down inhibitory avoidance (IA) retention. PD 098059 (50 microM) was bilaterally injected (0.5 microl/side) into the CA1 region of the dorsal hippocampus or entorhinal cortex at 0, 90, 180, or 360 min, or into the amygdala or parietal cortex at 0, 180, or 360 min after IA training in rats using a 0.4-mA foot shock. Retention testing was carried out 24 h after training. PD 098059 impaired retention when injected into the dorsal hippocampus at 180 min, but not 0, 90, and 360 min after training. When infused into the entorhinal cortex, PD 098059 was amnestic at 0 and 180 min, but not at 90 and 360 min after training. The MAPKK inhibitor also impairs IA retention when infused into the parietal cortex immediately after training, but not at 180 or 360 min. Infusions performed into amygdala were amnestic at 180 min, but not at 0 and 360 min after training. Our results suggest a time-dependent involvement of the MAPK cascade in the posttraining memory processing of IA; the time dependency is different in the hippocampus, amygdala, entorhinal cortex, or parietal cortex of rats.

Amygdala↗
PubMed2002

Role of dopamine, the frontal cortex and memory circuits in drug addiction: insight from imaging studies.

Drug addiction is characterized by a set of recurring processes (intoxication, withdrawal, craving) that lead to the relapsing nature of the disorder. We have used positron emission tomography to investigate in humans the role of dopamine (DA) and the brain circuits it regulates in these processes. We have shown that increases in DA are associated with the subjective reports of drug reinforcement corroborating the relevance of drug-induced DA increases in the rewarding effects of drugs in humans. During withdrawal we have shown in drug abusers significant reductions in DA D2 receptors and in DA release. We postulate that this hypodopaminergic state would result in a decreased sensitivity to natural reinforcers perpetuating the use of the drug as a means to compensate for this deficit and contributing to the anhedonia and dysphoria seen during withdrawal. Because the D2 reductions are associated with decreased activity in the anterior cingulate gyrus and in the orbitofrontal cortex we postulate that this is one of the mechanisms by which DA disruption leads to compulsive drug administration and the lack of control over drug intake in the drug-addicted individual. This is supported by studies showing that during craving these frontal regions become hyperactive in proportion to the intensity of the craving. Craving is also associated with activation of memory circuits including the amygdala (implicated in conditioned learning), hippocampus (implicated in declarative learning), and dorsal striatum (implicated in habit learning) all of which receive DA innervation. We therefore postulate that dopamine contributes to addiction by disrupting the frontal cortical circuits that regulate motivation, drive, and self-control and by memory circuits that increase the motivational salience of the drug and drug-associated stimuli.

Amygdala↗
PubMed1980

Gangliosides and thermal adaptation.

The concentration and pattern of brain gangliosides of lower and higher vertebrates were compared. Only when considering the eco-factor temperature clear correlations between systematical position of species, thermal adaptation status and brain ganglioside composition can be shown: lowering of the environmental temperature induces a long-term formation of more polar ganglioside fractions. In fishes additional long-term compensatory effects to changes in temperature were demonstrated with regard to motor activity, bioelectrical activity of the CNS (post-synaptic potential amplitude) and avoidance conditioning-learning. All phenomena taken together reflect a mechanism of modulating the thermo-sensitivity of the membrane-mediated processes of transmission.

Amphibians↗
PubMed1987

AI/LEARN: an interactive videodisk system for teaching medical concepts and reasoning.

This paper describes AI/LEARN, an educational videodisk system designed to teach clinical observational skills and reasoning in medicine. The AI/LEARN system uses a learning conditions approach to teaching. To teach visual concepts, we use the principle of exemplar/nonexemplar pairs and immediate feedback. To teach If-Then problem solving we use the format of minicases with delayed feedback. The software to operate the system has been custom developed and is domain independent. The result is a prototype of a new authoring package for videodisk teaching which operates on IBM compatible microcomputers. The medical domain selected for this prototype system was rheumatic diseases; the knowledge used to teach reasoning skills is derived from the knowledge base of an expert system: AI/RHEUM.

Computer Systems↗
PubMed1999

[Placebo effect in clinical trials].

BACKGROUND: It is well known that placebos evoke a variety of effects in the human body. It is less known that placebo medication can produce adverse drug reactions (ADRs). METHOD: The efficacy and, as the main topic, the tolerability were investigated from an international clinical data pool on placebo-controlled randomized multicenter studies of 5 different groups of indications. The therapeutic areas analyzed were neuropsychiatry (nimodipine, ipsapirone), cardiology (nisoldipine), metabolism (acarbose) and gastroenterology (hydrotalcit). RESULTS: The placebo efficacy was evident and varied not only in comparison to 5 indication groups analyzed, but also within them. Placebo showed for example hardly an effect on the symptomatology of stroke patients with a severe neurological deficit in comparison to verum while there was a 50% improvement in symptoms following placebo application in patients with a mild stroke. In angina patients exercise tolerance increased under placebo by 10% (time to onset of ST segment depression and symptoms of angina) while verum showed a 22% improvement. In diabetes placebo had no effect as compared to baseline and to a verum on blood glucose and HbA1C. ADRs could be observed under placebo treatment. The frequency and kind of placebo-induced ADRs varied also between the indication groups, i.e. typical CV side-effects were observed in CV controls. The placebo ADR profile was similar to the reference drug also. Some ADRs were reported even more frequently under placebo than under verum, like "dry mouth" in patients with general anxiety status. CONCLUSIONS: Placebo therapy is frequently effective and is not a "non-therapy". Placebo effects can be shown only by direct comparison with a "non-therapy". A placebo therapy is frequently accompanied by adverse drug reactions (ADRs) just as a verum therapy. Placebo ADRs are frequently illness- and verum-specific. Effects and ADRs of placebo therapy must be known, to judge the effect of verum medication in controlled clinical trials. The mechanisms of placebo effects are manifold (e.g. endorphine release, conditioned learning). Since placebo therapy outside of evidence-based medicine (use of drugs without proven efficacy = pseudoplacebos) may potentially also cause serious side effects, the use may not only be useless but also harmful.

Clinical Trials as Topic↗
PubMed2003

[Hyperacusis, phonophobia, and recruitment. Abnormal deviations of hearing associated with hypersensitivity to sound].

Hypersensitivity to sound is a common description of distinct nosological phenomena of peripheral and central hearing disorders, which are characterized by intense suffering from the acoustic environment. One can distinguish between recruitment accompanying inner ear hearing loss, hyperacusis with a general hypersensitivity to sound of any frequency, and phonophobia as an anxious sensitivity towards specific sound largely independent of its volume. While recruitment can be described as a peripheral reaction caused by a lack of outer hair cell moderation, hyperacusis and phonophobia represent disturbances of central auditory processing without peripheral pathology, often combined with psychosomatic reactions. Due to insufficient efferent inhibition, hyperacusis often follows psychovegetative exhaustion. In cases of phonophobia, peripheral and efferent hearing functions are usually intact, but certain learning (conditioning) processes lead to development of specific reactions and avoidance patterns to certain content-related acoustic stimuli. This article describes those different phenomena with regard to their clinical appearance, diagnostics, and possibilities for therapy.

Anxiety↗
PubMed2003

Effect of pheromones, hormones, and handling on sucrose response thresholds of honey bees (Apis mellifera L.).

The responsiveness of bees to sucrose is an important indicator of honey bee foraging decisions. Correlated with sucrose responsiveness is forage choice behavior, age of first foraging, and conditioned learning response. Pheromones and hormones are significant components in social insect systems associated with the regulation of colony-level and individual foraging behavior. Bees were treated to different exposure regimes of queen and brood pheromones and their sucrose responsiveness measured. Bees reared with queen or brood pheromone were less responsive than controls. Our results suggest responsiveness to sucrose is a physiologically, neuronally mediated response. Orally administered octopamine significantly reduced sucrose response thresholds. Change in response to octopamine was on a time scale of minutes. The greatest separation between octopamine treated and control bees occurred 30 min after feeding. There was no significant sucrose response difference to doses ranging from 0.2 mug to 20 mug of octopamine. Topically applied methoprene significantly increased sucrose responsiveness. Handling method significantly affected sucrose responsiveness. Bees that were anesthetized by chilling or CO(2) treatment were significantly more responsive than control bees 30 min after handling. Sixty minutes after handling there were no significant treatment differences. We concluded that putative stress effects of handling were blocked by anesthetic.

Anesthesia↗
PubMed1992

Cardiophobia: a paradigmatic behavioural model of heart-focused anxiety and non-anginal chest pain.

Cardiophobia is defined as an anxiety disorder of persons characterized by repeated complaints of chest pain, heart palpitations, and other somatic sensations accompanied by fears of having a heart attack and of dying. Persons with cardiophobia focus attention on their heart when experiencing stress and arousal, perceive its function in a phobic manner, and continue to believe that they suffer from an organic heart problem despite repeated negative medical tests. In order to reduce anxiety, they seek continuous reassurance, make excessive use of medical facilities, and avoid activities believed to elicit symptoms. The relationship of cardiophobia to illness phobia, health anxiety, and panic disorder is discussed. An integrative psychobiological model of cardiophobia is presented which includes previous learning conditions relating to experiences of separation and cardiac disease; deficient and inappropriate behavioural repertoires which constitute a psychological vulnerability for cardiophobic problems; negative life events, stressors, and conflicts in the person's present situation that trigger and contribute to the symptoms; current affective, cognitive, and behavioural symptoms and their stimulus properties; and genetic and acquired biological vulnerability factors. Finally, recommendations for the treatment of cardiophobia are derived from the model and areas of future research are outlined.

Arousal↗
PubMed1988

Recall of spatial location by the amnesic patient H.M.

The amnesic patient H.M. was tested for immediate recall of the location of objects in an array. Three array-sizes were used: 16, 7, or 4 objects. With 16 objects, H.M.'s performance was at chance level; with the smaller arrays, his performance was above chance, but still well below the levels achieved by age-matched control subjects. The ability to recall location by H.M. did not differ under incidental and intentional learning conditions, thus failing to support the notion that automatic encoding skills may be selectively disrupted in amnesia.

Amnesia↗
PubMed1995

Enhanced glutamatergic neurotransmission facilitates classical conditioning in the freely moving rat.

Centrally active drugs that enhance alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid receptor-gated currents by increasing the amplitude and duration of fast, excitatory synaptic responses in the hippocampus have recently been described. The effects of the compound 1-(1,3-benzodioxol-5-ylcarbonyl) perperidine (BDP) on associative and non-associative aspects of the classically conditioned eyeblink response in the freely moving rat were examined. Rats injected with BDP blinked significantly more to an acoustic stimulus of 85 dB than did vehicle controls, indicating that the drug enhances alpha responding to discrete auditory cues. Using a less intense stimulus of 80 dB, rats injected with BDP did not exhibit alpha responding or pseudo-conditioning, yet learned the conditioned response at a facilitated rate. These results suggest that increasing excitatory neurotransmission enhances the processing of sensory information and may contribute to subsequent contingency detection.

Acoustic Stimulation↗
PubMed2004

Peripheral arousal-related hormones modulate norepinephrine release in the hippocampus via influences on brainstem nuclei.

The peripheral hormone epinephrine (EPI) is known to modulate memory for arousing experiences. The mnemonic effects of EPI are attributed almost exclusively to actions on amygdala noradrenergic (NE) systems. EPI also increases neuronal activity in the locus coeruleus (LC), the primary source of NE to other limbic structures that process memory such as the hippocampus (HIPP). The actions of EPI on the LC suggest that its mnemonic properties may also be mediated by influencing NE output in the HIPP. To test this hypothesis, dialysate levels of NE were collected from the HIPP of male rats given an i.p. injection of saline that was followed 100 min later by i.p. EPI (0.3 mg/kg). NE levels sampled 20 min after EPI injection were significantly larger than baseline and continued to show significant peaks for 60 min. Experiment 2 examined whether peripheral signals initiated by EPI influence the HIPP via the nucleus of the solitary tract (NTS) by inactivating this nucleus with lidocaine prior to EPI injection. EPI injection did not increase NE levels sampled from the HIPP of rats given lidocaine into the NTS. EPI injection did produce significant elevations in HIPP NE levels in animals given a control solution into the NTS prior to the EPI injection. These findings indicate that the mnemonic effects of EPI reported in a wide range of learning conditions may not be mediated solely by NE release in the amygdala, but may also involve coactivation of the HIPP NE system.

Analysis of Variance↗
PubMed2005

Opposing influence of basolateral amygdala and footshock stimulation on neurons of the central amygdala.

BACKGROUND: The basolateral complex (BLA) and the central nucleus of the amygdala (CeA) are believed to mediate the expression of affective responses. After affective learning, conditioned stimulus-related information is thought to be conveyed from the BLA to the CeA; the medial CeA (Cem), in turn, projects to hypothalamic and brainstem structures involved with induction of affective responses. Although the conditioned stimulus and unconditioned stimulus both evoke affective responses, the precise response often differs. It is unknown whether this difference is represented by distinct activity patterns of single Cem neurons. Furthermore, the nature of the interaction between the BLA and Cem is unknown. METHODS: Using in vivo extracellular and intracellular recordings, we examined how the BLA affects the Cem and compared this with effects induced by footshock (unconditioned stimulus) in the same neurons. RESULTS: Our results demonstrate that, contrary to conventional views, BLA stimulation primarily inhibits Cem neurons by a polysynaptic circuit, and show that single Cem neurons respond to both BLA input and footshock in an opposite manner. CONCLUSIONS: These results demonstrate the predominantly inhibitory nature of the BLA-Cem interaction. These data further demonstrate the distinct cellular events that might lead to differential modulation of conditioned and unconditioned affective responses.

Action Potentials↗
PubMed2006

Methylphenidate improves reading performance in children with attention deficit hyperactivity disorder and comorbid dyslexia: an unblinded clinical trial.

Attention Deficit Hyperactivity Disorder (ADHD) and dyslexia are frequently co-occurring disorders. Although methylphenidate (MPH) is the primary treatment for ADHD, the effect on reading in children with these comorbid problems is not yet known. This study was an unblinded clinical trial to evaluate the reading performance before and after treatment with MPH. Reading performance was compared with General Linear Model repeated measures between three groups: (1) an experimental group of children with both ADHD and dyslexia (N = 24), (2) a control group of children with ADHD (N = 9) and (3) a control group of children with dyslexia (N = 10). MPH improved reading performance significantly stronger in the experimental group than in the control groups; the number of correctly read words increased to a larger extent. In conclusion, MPH proved to be an aid in the reading process of children with ADHD and comorbid dyslexia by improving the learning conditions, but MPH cannot cure the reading disorder. Future research should study the effect of MPH on reading in a double-blind clinical trial.

Adolescent↗
PubMed2004

Does the amygdala modulate adaptation to repeated stress?

Exposure of the rat to restraint results in activation of the hypothalamic-pituitary-adrenal (HPA) axis, a characteristic pattern of c-fos expression in the brain and increased cardiovascular function. These responses adapt with repeated exposure of an individual to the same stress. Corticosterone secretion habituates, and c-fos mRNA expression in the paraventricular nucleus of the hypothalamus (PVN) decreases. The increased expression of corticotropin releasing hormone mRNA in the PVN also becomes less prominent, whereas vasopressin mRNA progressively increases. The neural mechanisms responsible for this adaptation remain obscure. Because of its role in conditioned learning, we have hypothesised that the amygdala might be involved in this adaptive process. Here we show that large neurotoxic lesions of the amygdala in male rats do not prevent acute stress activation of the HPA axis following 30 min restraint, whilst more discrete lesions of the central nucleus actually exacerbate the acute response. Rats with large amygdala lesions demonstrate delayed habituation of corticosterone and c-fos to repeated restraint, an affect not apparent with central nucleus lesions. Furthermore we show that neither type of lesion significantly reduced tachycardiac responses to single or repeated restraint as measured by telemetry. We conclude that the amygdala and the central nucleus are not necessary for HPA and cardiovascular activation in response to stress (though the central nucleus may modulate it), and that adaptation to repeated stress is only modestly dependent upon the amygdala.

Acute Disease↗
PubMed2005

Mechanisms of placebo analgesia: rACC recruitment of a subcortical antinociceptive network.

Placebo analgesia is one of the most striking examples of the cognitive modulation of pain perception and the underlying mechanisms are finally beginning to be understood. According to pharmacological studies, the endogenous opioid system is essential for placebo analgesia. Recent functional imaging data provides evidence that the rostral anterior cingulate cortex (rACC) represents a crucial cortical area for this type of endogenous pain control. We therefore hypothesized that placebo analgesia recruits other brain areas outside the rACC and that interactions of the rACC with these brain areas mediate opioid-dependent endogenous antinociception as part of a top-down mechanism. Nineteen healthy subjects received and rated painful laser stimuli to the dorsum of both hands, one of them treated with a fake analgesic cream (placebo). Painful stimulation was preceded by an auditory cue, indicating the side of the next laser stimulation. BOLD-responses to the painful laser-stimulation during the placebo and no-placebo condition were assessed using event-related fMRI. After having confirmed placebo related activity in the rACC, a connectivity analysis identified placebo dependent contributions of rACC activity with bilateral amygdalae and the periaqueductal gray (PAG). This finding supports the view that placebo analgesia depends on the enhanced functional connectivity of the rACC with subcortical brain structures that are crucial for conditioned learning and descending inhibition of nociception.

Adolescent↗
PubMed1997

Evidence for a specific information processing deficit in monkeys with lesions of the septo-hippocampal system.

Monkeys with dysfunction of the septo-hippocampal system induced by excitotoxic lesion of the CA1 region of the hippocampus, or the septal/diagonal band area (which sends cholinergic projections to the hippocampus via the fornix), or with fornix transection were impaired on conditional learning tasks (when X choose A not B, when Y choose B not A) when trials with these different contingencies were presented in pseudorandom order but they were not impaired on learning this type of task if, prior to learning with trials in the pseudorandom order, the two types of trial had been presented in a fixed number of alternating batches of each type of trial. These results suggest that the septo-hippocampal system is required to process information in a particular type of way rather than to process a particular type of information and supports the view that the amnesia which results from medial temporal lobe damage in humans comprises an impairment of encoding information into long-term memory.

Amnesia↗
PubMed2000

The acallosal mouse strain I/LnJ: a putative model of ADHD?

ADHD has been sometimes associated to a defective interhemispheric cross-talk caused by hypoplasia of the corpus callosum. The inbred mouse strain I/LnJ shows total callosal agenesis with complete penetrance, and behavioral features which resemble ADHD. In conditioned learning tasks, as well as in paradigms of spontaneous behavior. I/LnJ mice, as compared to other inbred strains, show lower learning scores, impulsiveness, and significantly higher locomotor activity, albeit with considerable individual variations. In order to disentangle the influences of the genetic background from the effects of the callosal agenesis, we undertook crossing studies between I/LnJ and C57BL/6 mice, obtaining hybrids with missing corpus callosum. In comparison to normal C57BL/6 mice, acallosal hybrids exposed to a novel open-field showed a different locomotor pattern, with less short stops and more center crossing during the beginning of the session. In a metabolic mapping study, the tendency of acallosals to stay off the walls was found to be associated to lower 2-deoxyglucose uptake in the left striatum and cerebral cortex, while the number of short stops was correlated to the bilateral levels of 2-deoxyglucose uptake in the frontal and parietal cortex. The results hint at a right hemisphere dominance in impulsiveness and hyperactivity, boosted by the lack of callosal connections.

Agenesis of Corpus Callosum↗