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PubMed1994

Reversible inactivation of the lateral dorsal thalamus disrupts hippocampal place representation and impairs spatial learning.

Place-specific discharge of hippocampal cells was monitored while rats performed daily 15 trials of a spatial memory task. During the intertrial interval between trials 5 and 6, the lateral dorsal nucleus of the thalamus (LDN) was reversibly inactivated. Choice accuracy on the maze became impaired, and many hippocampal place fields became disrupted. These data support the proposition that the LDN passes onto hippocampus important (spatial) information that is used for accurate maze navigation.

Animals↗
PubMed1978

Mirex and behavior in the Long-Evans rat.

In two experiments, adult male Long-Evans rats were fed chow containing mirex (1.78 ppm and 17.8 ppm in Experiment 1, 17.8 ppm in Experiment 2) over a several week period and were tested on a variety of behavioral tasks. No differences in behavior were seen between control and experimental animals tested in an open-field apparatus, on VI 30-sec and DRL 20-sec operant paradigms, or on a discrimination-reversal task motivated by escape from footshock.

Animals↗
PubMed1990

Category discrimination by pigeons using five polymorphous features.

Eight pigeons were trained to discriminate between sets of color photographs of natural scenes. The scenes differed along five two-valued dimensions (site, weather, camera distance, camera orientation, and camera height), and all combinations of the feature values were used. One value of each dimension was designated as positive, and slides containing three or more positive feature values were members of the positive stimulus set. Thus, each feature had an equal, low, correlation with reinforcement, and all features had zero correlations with each other. Seven of the 8 pigeons learned this discrimination, and their responding came under the control of all five features. Within the positive and negative stimulus sets, response rates were higher to stimuli that contained more positive feature values. Once discrimination had been achieved, reversal training was given using a subset of the slides. In this subset, only a single feature was correlated with reinforcement. All pigeons learned this reversal successfully and generalized it to additional photographs with the same feature content. After reversal, the original reinforcement contingencies were reinstated, and training was continued using all the slides except those that had been used in reversal. Reversal generalized to these slides to some extent. Analysis of the response rates to individual slides showed that, compared with prereversal training, only the feature that had been subjected to reversal contingencies showed a reversed correlation with response rate. The remaining features showed the same correlation with response rate as they had before reversal training. Thus, reversal on some members of a category following category discrimination training led to generalization to stimuli within the category that were not involved in the reversal, but not to features that were not reversed. It is therefore inappropriate to refer to the pigeons as learning a concept.

Journal Article↗
PubMed2000

Action potential reflection and failure at axon branch points cause stepwise changes in EPSPs in a neuron essential for learning.

In leech mechanosensory neurons, action potentials reverse direction, or reflect, at central branch points. This process enhances synaptic transmission from individual axon branches by rapidly activating synapses twice, thereby producing facilitation. At the same branch points action potentials may fail to propagate, which can reduce transmission. It is now shown that presynaptic action potential reflection and failure under physiological conditions influence transmission to the same postsynaptic neuron, the S cell. The S cell is an interneuron essential for a form of nonassociative learning, sensitization of the whole body shortening reflex. The P to S synapse has components that appear monosynaptic (termed "direct") and polysynaptic, both with glutamatergic pharmacology. Reflection at P cell branch points on average doubled transmission to the S cell, whereas action potential failure, or conduction block, at the same branch points decreased it by one-half. Each of two different branch points affected transmission, indicating that the P to S connection is spatially distributed around these branch points. This was confirmed by examining the locations of individual contacts made by the P cell with the S cell and its electrically coupled partner C cells. These results show that presynaptic neuronal morphology produces a range of transmission states at a set of synapses onto a neuron necessary for a form of learning. Reflection and conduction block are activity-dependent and are basic properties of action potential propagation that have been seen in other systems, including axons and dendrites in the mammalian brain. Individual branch points and the distribution of synapses around those branch points can substantially influence neuronal transmission and plasticity.

Action Potentials↗
PubMed2003

Dissociating medial temporal and basal ganglia memory systems with a latent learning task.

The medial temporal (MT) lobes and basal ganglia have both been implicated as brain substrates of associative learning. Here, we show a dissociation between medial temporal and basal ganglia damage using a latent learning task, in which prior exposure to cues, uncorrelated with each other, slows subsequent learning of an association between them. Consistent with prior work, we found a robust exposure effect in healthy controls, with exposed controls learning more slowly than non-exposed controls. This effect was abolished in medial temporal amnesia: both exposed and non-exposed amnesic patients learned at the same speed. A group of patients with basal ganglia damage due to Parkinson's disease showed a reversal of the effect: exposed subjects learned faster than non-exposed subjects. Our findings point to distinct and dissociable contributions of medial temporal lobe and basal ganglia structures to learning and memory.

Adult↗
PubMed1980

Discrimination learning of an instrumental response in individual Drosophila melanogaster.

By using a unique methodology and a versatile series of choice points in two distinct apparatuses, individual Drosophila were shown to possess the ability to learn. This behavior can be controlled by a discriminative stimulus (substrate texture). Following a correct response in the presence of the discriminative stimulus at a horizontal choice point, fruit flies bred for negative geotaxis were given the opportunity to ascend a vertical alley leading to another choice point. When cues were consistent, reliable learning occurred. When cues were inconsistent, learning did not occur. Cue reversal produced the classic temporary increase in "incorrect" responses. The success of this paradigm is due, in large part, to the reduction of noxious and competing stimuli.

Animals↗
PubMed1993

Passive viewing of the Necker cube during massed and distributed practice.

Of 24 students from a psychology class in high school 12 were randomly assigned to a Massed Practice group (4 boys, 8 girls each) and 12 to a Distributed Practice group. They viewed a Necker cube for a 3-min. trial on three occasions separated by a week. The Massed Practice group had no rests while the Distributed Practice group rested 1 min. after each 1 min. of viewing. There were no significant differences for total reversals between Massed and Distributed groups on any trial. There were no significant differences between boys and girls on Trials 1 and 2, but on Trial 3 boys reported significantly more reversals than girls. Within each group there was a significant increase in the number of reversals from Trial 1 to Trial 3, indicating learning effects. Rigidity scores did not correlate significantly with the total Necker cube reversals for Trials 1, 2, or 3. The massed and distributed practice effects were not present although learning was noted. Longer rests may be needed for practice effects within trials; long rests of 7 days between trials may account for lack of differences.

Adolescent↗
PubMed1989

Autoshaping in micrencephalic rats.

An autoshaping procedure in which the illumination of a lever was predictive of food reinforcement was used to compare learning in rats with micrencephaly induced by irradiation on the 16th day of gestation and in sham-irradiated controls. Both groups showed equivalent levels of lever-directed activity, and the micrencephalic animals differentiated as well as the control animals between the predictive lever and a nonpredictive lever. The micrencephalic animals were able to redistribute their lever-directed activity when the significance of the levers was reversed and did so more readily than the control animals. Results support the claim that association learning survives either traumatic or developmental neocortical damage and have implications for remedial procedures following both head injury and developmental cerebral pathology in humans.

Animals↗
PubMed2004

Improvement of mouse memory by Myristica fragrans seeds.

Memory is one of the most complex functions of the brain and involves multiple neural pathways and neurotransmitter systems. The present study was undertaken to investigate the effect of Myristica fragrans (MF) seeds on learning and memory in mice. The n-hexane extract of MF was administered orally in three doses (5, 10, and 20 mg/kg p.o.) for 3 successive days to different groups of young and aged mice. The learning and memory parameters were assessed using elevated plus-maze and passive-avoidance apparatus. The effect of MF extract on scopolamine (0.4 mg/kg i.p.)- and diazepam (1 mg/kg i.p.)-induced impairment in learning and memory was also studied. MF extract at the lowest dose of 5 mg/kg p.o. administered for 3 successive days significantly improved learning and memory of young and aged mice. This extract also reversed scopolamine- and diazepam-induced impairment in learning and memory of young mice. MF extract enhanced learning and retention capacities of both young and aged mice. The exact mechanism of the memory-improving effect of MF extract was not explored in the present study. But, the observed memory-enhancing effect may be attributed to a variety of properties (individually or in combination) the plant is reported to possess, such as antioxidant, anti-inflammatory, or perhaps procholinergic activity.

Animals↗
PubMed2004

Memory-strengthening activity of Glycyrrhiza glabra in exteroceptive and interoceptive behavioral models.

In the traditional system of medicine, the roots and rhizomes of Glycyrrhiza glabra have been employed clinically for centuries for their anti-inflammatory, anti-ulcer, expectorant, antimicrobial, and anxiolytic activities. The present study was undertaken to investigate the effects of G. glabra, popularly known as liquorice (Mulathi), on learning and memory. The elevated plus-maze and passive avoidance paradigm were employed to evaluate learning and memory parameters. Three doses (75, 150, and 300 mg/kg p.o.) of aqueous extract of G. glabra were administered for 7 successive days in separate groups of mice. The dose of 150 mg/kg of the aqueous extract of liquorice significantly improved learning and memory of mice. Furthermore, this dose reversed the amnesia induced by diazepam (1 mg/kg i.p.), scopolamine (0.4 mg/kg i.p.), and ethanol (1 g/kg i.p.). Anti-inflammatory and antioxidant properties of liquorice may be contributing favorably to the memory enhancement effect. Since scopolamine-induced amnesia was reversed by liquorice, it is possible that the beneficial effect on learning and memory may be because of facilitation of cholinergic transmission in brain. However, further studies are necessitated to identify the exact mechanism of action. In the present investigation, G. glabra has shown promise as a memory enhancer in both exteroceptive and interoceptive behavioral models of memory.

Administration, Oral↗
PubMed1996

Influence of antidepressant drugs on learning and memory paradigms in mice.

Effect of antidepressant drugs (amitriptyline, imipramine and fluoxetine) on cognitive functions, impaired by the muscarinic antagonist scopolamine were investigated in mice. The changes in learning and memory tasks were studied using transfer latency on elevated plus maze and employing number of descents in passive avoidance paradigms. Amitriptyline and imipramine showed significant memory impairment. They also potentiated scopolamine-induced memory deficit in a significant way. Amitriptyline and imipramine impair cognitive function possibly due to their anticholinergic properties. Fluoxetine, a newer antidepressant, however showed no effect on learning and memory. It significantly reversed the scopolamine-induced memory impairment in both the tests. Fluoxetine with no anticholinergic property may prove to be a better drug in endogenous depression in elderly patients.

Aged↗
PubMed1986

The lesion of serotonergic neurons does not prevent antidepressant-induced reversal of escape failures produced by inescapable shocks in rats.

The present study was aimed at testing the hypothesis (based mainly on biochemical evidence) of the implication of brain serotonergic neurons in the induction of learned helplessness (escape deficit) and its reversal by antidepressants in rats. After desipramine (25 mg/kg IP)-pretreatment rats were either sham-operated or infused with 5,7-dihydroxytryptamine (5,7-DHT, 3 micrograms of free base in 0.4 microliter saline containing 0.02% ascorbic acid) into the midbrain raphe area. Three weeks later, experimental animals were exposed to 60 randomized inescapable shocks (0.8 mA; 15 sec duration), control rats being not shocked, and 48 hr later, they were subjected to daily shuttle-box sessions (30 trials/day; ITI = 30 sec) on 3 consecutive days in order to assess escape deficits. After inescapable shock pretreatment separate groups of rats were given twice daily injections of clomipramine (total daily dose: 32 mg/kg), desipramine (24 mg/kg), imipramine (32 mg/kg), nialamide (32 mg/kg) or saline. After behavioral testing, animals were sacrificed, and tryptophan hydroxylase activity was assayed in the cerebral cortex, the hippocampus and the striatum. We found that damage to serotonergic neurons associated with a 70% loss of tryptophan hydroxylase activity altered neither escape deficits produced by prior exposure to inescapable shock, nor the ability of either antidepressant studied to reverse escape failures in the shuttle-box paradigm. These findings cast some doubts on the hypothesized crucial role of serotonergic neurons in helpless behavior and its reversal by antidepressants.

Animals↗