Neurobiology of learning and memory
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Neurobiol Learn Mem · Nov 2006
Comparative StudyThe level of cholinergic nucleus basalis activation controls the specificity of auditory associative memory.
Learning involves not only the establishment of memory per se, but also the specific details of its contents. In classical conditioning, the former concerns whether an association was learned while the latter discloses what was learned. The neural bases of associativity have been studied extensively while neural mechanisms of memory specificity have been neglected. ⋯ The degree of memory specificity 24 h after training was positively correlated with the magnitude of CS-elicited increase in gamma activity within the EEG during training, but only in the moderate NBs group. Thus, a low level of acetylcholine released by the nucleus basalis during learning is sufficient to induce associativity whereas a higher level of release enables the storage of greater experiential detail. gamma waves, which are thought to reflect the coordinated activity of cortical cells, appear to index the encoding of CS detail. The findings demonstrate that the amount of detail in memory can be directly controlled by neural intervention.
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Neurobiol Learn Mem · Sep 2006
Comparative StudyIndividual differences in anxiety trait are related to spatial learning abilities and hippocampal expression of mineralocorticoid receptors.
Although high levels of anxiety might be expected to negatively influence learning and memory, it remains to be shown whether individual differences in anxiety may influence spatial learning and memory in outbred rat populations. We have studied this possibility in male Wistar rats whose levels of anxiety were first characterized as either high (HA) or low (LA) according to their behavior in the elevated plus maze or in the open field test. Subsequently, their performance in the Morris water maze was studied, a task dependent on hippocampal activity. ⋯ Indeed, the expression levels for these receptors were positively correlated with the amount of time spent by the animals in the open arms of the elevated plus maze. Moreover, we present evidence that the levels of anxiety quantified in the first stages of our study constitute a trait rather than a state. Taken together, this study has generated evidence of a close interaction between the anxiety trait, hippocampal MR expression and the learning abilities of individuals in stressful spatial orientation tasks.
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Neurobiol Learn Mem · Sep 2006
Comparative StudyWistar rats with high versus low rearing activity differ in radial maze performance.
Substantial work has shown that rats although identical in stock, sex, age, and housing conditions can differ considerably in terms of behavior and physiology. Such individual differences, which can be detected by specific behavioral screening tests, are rather stable, that is, they probably reflect a behavioral disposition or trait. Here, we asked whether and how such differences might affect performance in a task of spatial learning and memory, the radial maze. ⋯ In general, working memory errors were more frequent in the arm with the large bait size, but there were no indications that HRA and LRA rats responded differently dependent on reward size. Finally, LRA rats lost slightly more weight than HRA rats during the period of food deprivation. These results are discussed with respect to the role of cognitive and motivational mechanisms, which as subject-inherent factors can contribute substantially to inter-individual variability in the radial maze.
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Neurobiol Learn Mem · Jul 2006
Comparative StudyRapid induction of specific associative behavioral memory by stimulation of the nucleus basalis in the rat.
Hypothesized circuitry enabling behavioral memory formation can be tested by its direct activation in the absence of normal experience. Neuromodulation via the cortical release of acetylcholine by the nucleus basalis (NB) is hypothesized to be sufficient to induce specific, associative behavioral memory. Previously, we found that tone paired with stimulation of the nucleus basalis (NBs) for 3000 trials over 15 days induced such memory, supporting the hypothesis. ⋯ Post-training behavioral generalization gradients exhibited response peaks centered on the CS frequency for the Paired group alone. Tone evoked potentials from the ACx also developed CS-specific plasticity. The findings indicate that NB induction of specific behavioral associative memory, like normal memory, can develop rapidly and is accompanied by specific cortical plasticity, supporting the view that NB engagement during normal learning produces memory.
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Human episodic memory refers to the recollection of an unique past experience in terms of its details, its locale, and temporal occurrence. Episodic memory, even in principle, has been difficult to demonstrate in non-verbal mammals. Previously, we provided evidence that mice are able to form an integrated memory for "what," "where," and "when" aspects of single experiences by combining different versions of the novelty-preference paradigm, i.e., object recognition memory, the memory for locations in which objects were explored, and the temporal order memory for objects presented at distinct time points. ⋯ We found that rats spent more time exploring an "old familiar" object relative to a "recent familiar" object, suggesting that they recognized objects previously explored during separate trials and remembered their order of presentation. Concurrently, the rats responded differentially to spatial object displacement dependent on whether an "old familiar" or "recent familiar" object was shifted to a location, where it was not encountered previously. These results provide strong evidence that the rats established an integrated memory for "what," "where," and "when." We also found that acute stress impaired the animal's performance in the episodic-like memory task, which, however, could be partially reversed by the N-Methyl-D-aspartate-receptors agonist D-cycloserine.