Acetylcholine and olfactory perceptual learning - PubMed (original) (raw)

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Acetylcholine and olfactory perceptual learning

Donald A Wilson et al. Learn Mem. 2004 Jan-Feb.

Abstract

Olfactory perceptual learning is a relatively long-term, learned increase in perceptual acuity, and has been described in both humans and animals. Data from recent electrophysiological studies have indicated that olfactory perceptual learning may be correlated with changes in odorant receptive fields of neurons in the olfactory bulb and piriform cortex. These changes include enhanced representation of the molecular features of familiar odors by mitral cells in the olfactory bulb, and synthetic coding of multiple coincident odorant features into odor objects by cortical neurons. In this paper, data are reviewed that show the critical role of acetylcholine (Ach) in olfactory system function and plasticity, and cholinergic modulation of olfactory perceptual learning at both the behavioral and cortical level.

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Figure 1

Odor discrimination is enhanced by experience and modulated by acetylcholine. (A) Following 50 sec of exposure to a novel binary mixture, olfactory bulb mitral cells show poor discrimination of the mixture from its components (strong cross-habituation), while cells in the anterior piriform cortex could show discrimination (only weak cross habituation). The enhanced cortical discrimination, however, requires sufficient past experience. Exposure to a novel mixture for only 10 sec is insufficient to allow good discrimination between the mixture and its components. These data are consistent with experience-dependent synthetic coding in the piriform cortex, with familiar mixtures treated as unique odor objects, distinct from their components (from Wilson 2003). (B) The experience-induced enhancement in cortical odor discrimination can be blocked by application of the muscarinic receptor antagonist scopolamine to the piriform cortical surface during exposure to the novel odorant. Similar results are observed after systemic 0.5 mg/kg scopolamine injections. In this example, cells are tested for discrimination of alkanes differing in carbon chain length (from Wilson 2001). (C) Prior exposure enhances discriminability of similar odorants (ethyl esters varying in carbon chain length) behaviorally, as assessed with odor-evoked cardiac orienting responses (cf. trained vs. untrained cross-habituation). Systemic scopolamine during the training phase prevents this perceptual learning (from Fletcher and Wilson 2002).

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