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PubMed1981

Characteristics of predoctoral endodontic education in the United States and Canada.

A survey was conducted to assess the current state of predoctoral endodontic education programs in United States and Canadian dental schools. The investigation focused on faculty characteristics, the learning climate for endodontics, and problems of administration. Comparison was made between current learning conditions in the schools and desirability of these conditions. Comparisons also were made between large and small schools. Endodontic program directors identified numerous conditions associated with the enhancement of learning. Problems reported were inadequate time to pursue research and scarcity of full-time faculty in some programs.

Administrative Personnel↗
PubMed1991

Brain stem mechanisms of conditioned taste aversion learning in rats.

Acquisition of conditioned taste aversion (CTA) in rats is not prevented by functional decortication, anesthesia or hypothermia applied after intake of the flavored fluid and maintained throughout the action of the poison but is disrupted by bilateral application of 10 ng tetrodotoxin (TTX) into the parabrachial nuclei. The blockade is directly proportional to TTX dosage, indirectly proportional to distance of the injection site from parabrachial nuclei and equally affects CTAs using different CS (saccharin, NaCl) and different US (LiCl, carbachol, amphetamine, cycloheximide). CTA is disrupted by TTX applied up to 4 but not 8 days after a single CS-US pairing. TTX fails to disrupt overtrained CTA and elicits only a weak anterograde amnesia when applied 1 but 2 or more days before CTA acquisition. It is concluded that the parabrachial nuclei and the adjacent reticular formation probably represent the neural substrate of the permanent CTA engram the protracted consolidation of which is disrupted by prolonged cessation of impulse which is disrupted by prolonged cessation of impulse activity in the information storing network.

Amnesia↗
PubMed1991

Acquisition and retention by hippocampal rats of simple, conditional, and configural tasks using tactile and olfactory cues: implications for hippocampal function.

Hippocampal rats were given simple, conditional, and configural tasks that required them to pull up strings to obtain food pellets. The tasks contrasted string size, odor, location, paired string size and location, or compounds of string size and odor. There was no anterograde or retrograde amnesia for the simple discriminations or for simple discrimination components of the other tasks. Hippocampal rats also learned conditional and configural tasks, although they were impaired on the configural task. Finally, the rats were impaired in postoperative retention of the conditional but not the configural task, although they displayed savings in relation to naive rats on the conditional task. The results do not support theories that the hippocampus is essential for conditional or configural learning but may support a modified form of configural theory in which the hippocampus contributes to, but is not essential for, learning or retention of configurations.

Animals↗
PubMed2006

Altered gene activity correlated with long-term memory formation of conditioned taste aversion in Lymnaea.

The pond snail Lymnaea stagnalis is capable of learning conditioned taste aversion (CTA) and then consolidating that learning into long-term memory (LTM) that persists for at least 1 month. LTM requires de novo protein synthesis and altered gene activity. Changes in gene activity in Lymnaea that are correlated with, much less causative, memory formation have not yet been identified. As a first step toward rectifying this situation, we constructed a cDNA microarray with mRNAs extracted from the central nervous system (CNS) of Lymnaea. We then, using this microarray assay, identified genes whose activity either increased or decreased following CTA memory consolidation. We also identified genes whose expression levels were altered after inhibition of the cyclic AMP response element-binding protein (CREB) that is hypothesized to be a key transcription factor for CTA memory. We found that the molluscan insulin-related peptide II (MIP II) was up-regulated during CTA-LTM, whereas the gene encoding pedal peptide preprohormone (Pep) was down-regulated by CREB2 RNA interference. We next examined mRNAs of MIP II and Pep using real-time RT-PCR with SYBR Green. The MIP II mRNA level in the CNS of snails exhibiting "good" memory for CTA was confirmed to be significantly higher than that from the CNS of snails exhibiting "poor" memory. In contrast, there was no significant difference in expression levels of the Pep mRNA between "good" and "poor" performers. These data suggest that in Lymnaea MIP II may play a role in the consolidation process that forms LTM following CTA training.

Analysis of Variance↗
PubMed1998

Modifications of reward expectation-related neuronal activity during learning in primate striatum.

This study investigated neuronal activity in the anterior striatum while monkeys repeatedly learned to associate new instruction stimuli with known behavioral reactions and reinforcers. In a delayed go-nogo task with several trial types, an initial picture instructed the animal to execute or withhold a reaching movement and to expect a liquid reward or not. During learning, new instruction pictures were presented, and animals guessed and performed one of the trial types according to a trial-and-error strategy. Learning of a large number of pictures resulted in a learning set in which learning took place in a few trials and correct performance exceeded 80% in the first 60-90 trials. About 200 task-related striatal neurons studied in both familiar and learning conditions showed three forms of changes during learning. Activations related to the preparation and execution of behavioral reactions and the expectation of reward were maintained in many neurons but occurred in inappropriate trial types when behavioral errors were made. The activations became appropriate for individual trial types when the animals' behavior adapted to the new task contingencies. In particular, reward expectation-related activations occurred initially in both rewarded and unrewarded movement trials and became subsequently restricted to rewarded trials. These changes occurred in parallel with the visible adaptation of reward expectations by the animals. The second learning change consisted in decreases of task-related activations that were either restricted to the initial trials of new learning problems or persisted during the subsequent consolidation phase. They probably reflected reductions in the expectation and preparation of upcoming task events, including reward. The third learning change consisted in transient or sustained increases of activations. These might reflect the increased attention accompanying learning and serve to induce synaptic changes underlying the behavioral adaptations. Both decreases and increases often induced changes in the trial selective occurrence of activations. In conclusion, neurons in anterior striatum showed changes related to adaptations or reductions of expectations in new task situations and displayed activations that might serve to induce structural changes during learning.

Animals↗
PubMed1990

Memory for temporal order and conditional associative-learning in patients with Parkinson's disease.

The performance of Parkinson's patients was compared to that of normal controls on memory for temporal order and conditional associative-learning tasks, each of which is sensitive to frontal-lobe dysfunction. Memory for temporal order involved reconstructing the presentation order of each of a series of drawings, words and designs. Recognition of similar stimuli was also examined. Parkinson's patients exhibited poor memory for the relative temporal relations between stimuli, though no group differences were observed in the number of stimuli placed in the correct position. Recognition was intact in the Parkinson's patients, and an absence of correlation between performance on the recognition and temporal order tasks indicates that the poor memory for temporal order is not simply a function of degraded memory for the individual stimuli. The conditional associative-learning task required subjects to learn, either by trial-and-error or with immediate correction, numbers paired with drawings, designs or spatial locations. Parkinson's patients were impaired only when learning by trial-and-error was required. Results suggest that the strategic retrieval processes involved in both memory for temporal order and learning conditional associations by trial-and-error depend on the integrity of the fronto-striatal system, which is known to be affected in Parkinson's disease.

Aged↗
PubMed2001

A role for dopamine D1 receptors of the nucleus accumbens shell in conditioned taste aversion learning.

The involvement of dopamine (DA) in conditioned taste aversion (CTA) learning was studied with saccharin or sucrose as the conditioned stimulus (CS) and intraperitoneal lithium as the unconditioned stimulus (US). The dopamine D(1) antagonist R(+)-7-chloro-8-hydroxy-3-methyl-1-phenyl-2,3,4,5-tetrahydro-1H-3-benzazepine hydrochloride (SCH 23390) (12.5-50 microg/kg, s.c.), given 5 min after the CS, impaired the acquisition of CTA in a paradigm consisting of three or a single CS-lithium association. SCH 23390 failed to impair CTA acquisition given 45 min after, 30 min before, or right before the CS. (-)-trans-6,7,7a,8,9,13b-hexahydro-3-chloro-2-hydroxy-N-methyl-5a-benzo-(d)-naphtho-(2,1b) azepine (SCH 39166) (12.5-50.0 microg/kg, s.c), a SCH 23390 analog that does not bind to 5HT(2) receptors, also impaired CTA. No significant impairment of CTA was obtained after administration of the specific D(2)/D(3) antagonist raclopride (100 and 300 microg/kg, s.c.). The ability of SCH 23390 to impair CTA learning was confirmed by its ability to reduce the conditional aversive reactions to a gustatory CS (sweet chocolate) as estimated in a taste reactivity paradigm. SCH 39166 impaired CTA also when infused in the nucleus accumbens (NAc) shell 5 min after the CS. No impairment was obtained from the NAc core or from the bed nucleus stria terminalis. The results indicate that D(1) receptor blockade impairs CTA learning by disrupting the formation of a short-term memory trace of the gustatory CS and that endogenous dopamine acting on D(1) receptors in the NAc shell plays a role in short-term memory processes related to associative gustatory learning.

Animals↗
PubMed2004

Effect of low doses of delta9-tetrahydrocannabinol and cannabidiol on the extinction of cocaine-induced and amphetamine-induced conditioned place preference learning in rats.

RATIONALE: Using the place-preference conditioning paradigm, we evaluated the potential of the two most prominent cannabinoids found in marijuana, the psychoactive component delta9-tetrahydrocannabinol (delta9-THC) and the nonpsychoactive component cannabidiol (CBD), to potentiate extinction of a cocaine-induced and an amphetamine-induced conditioned place preference in rats. METHODS: To determine the effects of pretreatment with delta9-THC or CBD on extinction, a cocaine-induced and amphetamine-induced place preference was first established. Rats were then given an extinction trial, during which they were confined to the treatment-paired floor for 15 min. Thirty minutes prior to the extinction trial, they were injected with a low dose of delta9-THC (0.5 mg/kg), CBD (5 mg/kg) or vehicle. The potential of the CB1 receptor antagonist, SR141716, to reverse the effects of delta9-THC or CBD was also evaluated. To determine the hedonic effects of CBD, one distinctive floor was paired with CBD (5 mg/kg) and another with saline. Finally, to determine the effect of delta9-THC.or CBD on the establishment and/or the expression of a place preference during four cycles of conditioning trials, rats were injected with delta9-THC (0.25-1 mg/kg), CBD (5 mg/kg) or vehicle 25 min prior to receiving an injection of amphetamine followed by placement on the treatment floor; on alternate days, they received injections of vehicle followed by saline and placement on the nontreatment floor. The rats then received two test trials; on one trial they were pretreated with the cannabinoid and on the other trial with vehicle. RESULTS: delta9-THC and CBD potentiated the extinction of both cocaine-induced and amphetamine-induced conditioned place preference learning, and this effect was not reversed by SR141716. The cannabinoids did not affect learning or retrieval, and CBD was not hedonic on its own. CONCLUSIONS: These results are the first to show that both delta9-THC, which acts on both CB 1 and CB2 receptors, and CBD, which does not bind to CB1 or CB2 receptors, potentiate the extinction of conditioned incentive learning.

Amphetamine↗
PubMed2000

Verbal learning strategies in patients with multiple sclerosis.

Word list learning was studied in patients with a definite diagnosis of Multiple Sclerosis and in Normal Control subjects by means of the selective reminding procedure of Buschke and Fuld in two learning conditions: (1) using unrelated items and (2) paired-associate items. The Multiple Sclerosis patients displayed poor learning in both conditions. To identify the functional locus of their deficit, stochastic Markov chain analyses were performed, which allowed individual measurements of encoding, automatic and intentional retrieval abilities. On both tasks, encoding on the first trial and automatic retrieval on the subsequent trials were impaired in Multiple Sclerosis patients, whereas intentional retrieval, both with and without reminding by the examiner, appeared to be preserved. As all of the impaired abilities require a normal speed of information processing, the salient learning deficit of the Multiple Sclerosis patients could be tentatively traced back to the slowing down of their mental activity.

Adult↗
PubMed1999

Levels-of-processing effects in subject-performed tasks.

In memory for subject-performed tasks (SPTs), subjects encode a list of simple action phrases (e.g., thumb through a book, knock at the door) by performing these actions during learning. In three experiments, we investigated the size of the levels-of-processing effects in SPTs as compared with those in standard verbal learning tasks (VTs). Subjects under SPT and VT conditions learned lists of action phrases in a surface or a conceptual orienting task. Under both encoding conditions, the subjects recalled fewer items with surface orienting tasks than with conceptual orienting tasks, but the levels-of-processing effects were strongly reduced in the SPT condition. In the SPT condition, items that were encoded in a surface orienting task were still substantially recalled. The items were recalled almost as well as the conceptually encoded items in the VT condition. The distinct reduction of the levels-of-processing effect is caused by the fact that, in SPT encoding even with a verbal surface orienting task, subjects process conceptual information in order to perform the denoted action. We attribute the small conceptual advantage, which remains with SPT despite the conceptual processing for performing, to the fact that items are not as well integrated into memory as they are when conceptual processing is focused on the action component, rather than on the semantic contexts. This lower integration reduces the accessibility of items in the verbal surface task, even with SPT encoding.

Adult↗
PubMed1986

Stimulus definition in conditional discriminations.

With a customary arrangement of three horizontally aligned stimulus/response keys, two rhesus monkeys learned conditional hue and line discriminations--an "identity-matching" procedure. First, sample stimuli were presented on the center key, and comparison stimuli were presented on the two side keys. Next, the sample was allowed to appear on any one of the three keys, with the comparisons on the remaining two. The change from fixed to variable sample and comparison locations caused the horizontal and vertical lines to lose control over the animals' responses; the conditional hue discrimination remained intact. Accurate description of controlling stimuli in a matching-to-sample procedure may therefore require that their spatial location be specified.

Animals↗
PubMed1999

Classical conditioning during nitrous oxide treatment: influence of varying the interstimulus interval.

Classical conditioning of the rabbit nictitating membrane response (NMR) was accomplished by presenting a 75-ms tone conditioned stimulus (CS) at intervals of 0, 100, 200, 400, and 800 ms before the presentation of a 100-ms shock unconditioned stimulus. Following every four paired trials (tone followed by shock), the occurrence of conditioned responses (CRs) was tested on every fifth trial in which only tone was presented (test trials). Three doses of nitrous oxide in oxygen (0, 33, and 67%) were used during conditioning. Nitrous oxide produced dose-dependent decrements of learning. Conditioned responding was related to the interstimulus interval (ISI) by a concave-down function. The higher dose of nitrous oxide caused more decrements of learning at several ISIs compared to the other two doses, changing the shape of the curve. Trace conditioning, which was examined in the present study, was more impaired under the influence of nitrous oxide than conditioning in a previous study, which used the standard delay paradigm. Thus, the drug impairs explicit memory more than implicit memory.

Acoustic Stimulation↗
PubMed1986

Learned helplessness as conditioned inattention to the target stimulus.

Learned helplessness theory explains the impaired performance that follows exposure to uncontrollable outcomes by assuming learned expectation of response-outcome independence that is transferred between tasks. Recent evidence has shown that introducing a second neutral stimulus, contingent on the offset of the uncontrollable stimulus, removes the subsequent interference. This finding has been claimed to support the view that the interference is a result of conditioned inattention rather than of the expectation of response-outcome independence. These conflicting explanations were examined in a series of four experiments that varied induction procedures (passive exposure or inescapability) and stimulus quality (aversive or nonaversive). All four experiments found the predicted interference, but only one, in which passive exposure was combined with an aversive stimulus, obtained results supporting the conditioned inattention hypothesis. We conclude that learned helplessness probably involves more than a single mechanism and that the passive exposure procedure may not be appropriate for demonstrating genuine helplessness deficits.

Adult↗
PubMed1984

Incidental psychomotor learning: the effects of number of movements, practice, and rehearsal.

Three experiments were conducted to investigate the effects of the number of movements, practice, and rehearsal on incidental and intentional psychomotor learning. incidental learners received no formal instructions to learn the central task to which they were exposed in a choice reaction-time task. The movements to the targets in this task comprised a movement sequence. Intentional learners also performed the choice reaction-time task but were additionally instructed to remember the order of the movements. Intentional learning was superior to incidental learning, unless rehearsal was disrupted; all three independent variables demonstrated similar functional effects under both learning conditions. It was concluded that incidental and intentional learning are not distinct types of learning; and that "intent to learn" per se is a significant factor in psychomotor learning only when it elicits beneficial cognitive processes such as rehearsal.

Journal Article↗
PubMed1987

A neuronal network model of associative memory and a brain theory.

There are facts suggesting that the changes of excitability of neurons and conductance of synapses are responsible for learning and memory. In accordance with the idea, the author proposed a neuronal network model of associative memory, which can learn conditioned reflexes repeatedly together with its adaptive properties, without much interference with the previously existing memories. Further, a modified model can memorize dynamic images and establish motor patterns. An analysis of the structure of the model is presented, and some conclusions about this sort of model are drawn. A theory of memory and learning suggesting that the brain works by means of a mechanism similar to that of the model is proposed, as well as the explanations for some behavioral and clinical findings from the viewpoint of the model.

Animals↗