Neurobiology of learning and memory
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Neurobiol Learn Mem · Nov 2005
Integrated memory for objects, places, and temporal order: evidence for episodic-like memory in mice.
Human episodic memory refers to the recollection of an unique past experience in terms of what happened, and where and when it happened. Factoring out the issue of conscious recollection, episodic memory, even at the behavioral level, has been difficult to demonstrate in non-human mammals. Although, it was previously shown that rodents can associate what and when or what and where information given on unique trials, it proved to be difficult to demonstrate memory for what, where, and when simultaneously in mammals, without using extensive training procedures, which might induce semantic rather than episodic memory recall. ⋯ We found that mice spent more time exploring two "old familiar" objects relative to two "recent familiar" objects, reflecting memory for what and when and concomitantly directed more exploration at a spatially displaced "old familiar" object relative to a stationary "old familiar" object, reflecting memory for what and where. These results suggest that during a single test trial the mice were able to (a) recognize previously explored objects, (b) remember the location in which particular objects were previously encountered, and (c) to discriminate the relative recency in which different objects were presented. According to the currently discussed behavioral criteria for episodic-like memory in animals, our results suggest that mice are capable to form such higher order memories.
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Neurobiol Learn Mem · Mar 2005
Retrieval improvement is induced by water shortage through angiotensin II.
Angiotensin II (ANGII) has an evolutionary preserved role in determining adaptative responses to water-shortages. In addition, it has been shown to modulate diverse phases of memory. Still, it is not clear whether ANGII improves or spoils memory. ⋯ We conclude that ANGII released due to water shortage leads to enhanced memory retrieval. Thus, it seems that ANGII has an evolutionary preserved role as a multifunction coordinator that enables an adaptative response to water-shortage. The facilitation of memory consolidation and retrieval would be among those coordinated functions.
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Neurobiol Learn Mem · Jan 2005
Comparative StudyTraining-induced and electrically induced potentiation in the neocortex.
Long-term potentiation (LTP) shares many properties with memory and is currently the most popular laboratory model of memory. Although it has not been proven that memory is based on an LTP-like mechanism, there is evidence that learning a motor skill can induce LTP-like effects. This evidence was obtained in a slice-preparation experiment, which precluded within-animal comparisons before and after training. ⋯ Evoked potentials were found to be larger in motor cortex layer II/III in the trained, compared to the untrained, hemisphere in slice, acute, and chronic preparations. Consistent with previous research, the trained hemisphere was less amenable to subsequent LTP induction. Furthermore, the application of either LTP- or LTD-inducing stimulation during the training phase of the reaching task disrupted the acquisition of the skill, providing further evidence that memory may be based on an LTP mechanism.
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Neurobiol Learn Mem · Nov 2003
ReviewThe nucleus basalis and memory codes: auditory cortical plasticity and the induction of specific, associative behavioral memory.
Receptive field (RF) plasticity develops in the primary auditory cortex (ACx) when a tone conditioned stimulus (CS) becomes associated with an appetitive or aversive unconditioned stimulus (US). This prototypical stimulus-stimulus (S-S) association is accompanied by shifts of frequency tuning of neurons toward or to the frequency of the CS such that the area of best tuning of the CS frequency is increased in the tonotopic representation of the ACx. RF plasticity has all of the major characteristics of behavioral associative memory: it is highly specific, discriminative, rapidly induced, consolidates (becomes stronger and more specific over hours to days) and can be retained indefinitely (tested to two months). ⋯ The degree of acquired behavioral significance of sounds appears to be encoded by the number of neurons that become retuned in the ACx to that acoustic stimulus, the greater the importance, the greater the number of re-tuned cells. This memory code has recently been supported by direct neurobehavioral tests. In toto, these findings support the view that specific, learned auditory memory content is stored in the ACx, and further that this storage of information during learning and the instantiation of the memory code involves the engagement of the nucleus basalis and its release of acetylcholine into target structures, particularly the cerebral cortex.
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Drugs of abuse cause long-lasting changes in the brain that underlie the behavioral abnormalities associated with drug addiction. Similarly, experience can induce memory formation by causing stable changes in the brain. Over the past decade, the molecular and cellular pathways of drug addiction, on the one hand, and of learning and memory, on the other, have converged. ⋯ Complex circuits involving the hippocampus, cerebral cortex, ventral and dorsal striatum, and amygdala are implicated both in addiction and in learning and memory. The complexity of the plasticity that occurs in these circuits can be illustrated by CREB, which induces very different behavioral effects in these various brain regions. A better understanding of the molecular and cellular adaptations that occur in these neural circuits may lead to novel interventions to improve memory and combat addiction in humans.