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      Profound Context-Dependent Plasticity of Mitral Cell Responses in Olfactory Bulb

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      PLoS Biology

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          There is no author summary for this article yet. Authors can add summaries to their articles on ScienceOpen to make them more accessible to a non-specialist audience.

          Abstract

          On the basis of its primary circuit it has been postulated that the olfactory bulb (OB) is analogous to the retina in mammals. In retina, repeated exposure to the same visual stimulus results in a neural representation that remains relatively stable over time, even as the meaning of that stimulus to the animal changes. Stability of stimulus representation at early stages of processing allows for unbiased interpretation of incoming stimuli by higher order cortical centers. The alternative is that early stimulus representation is shaped by previously derived meaning, which could allow more efficient sampling of odor space providing a simplified yet biased interpretation of incoming stimuli. This study helps place the olfactory system on this continuum of subjective versus objective early sensory representation. Here we show that odor responses of the output cells of the OB, mitral cells, change transiently during a go–no-go odor discrimination task. The response changes occur in a manner that increases the ability of the circuit to convey information necessary to discriminate among closely related odors. Remarkably, a switch between which of the two odors is rewarded causes mitral cells to switch the polarity of their divergent responses. Taken together these results redefine the function of the OB as a transiently modifiable (active) filter, shaping early odor representations in behaviorally meaningful ways.

          Author Summary

          The way in which the brain represents and processes sensory information remains a fundamental question. One model posits that stable neural representation of a stimulus during early stages of stimulus processing allows for unbiased interpretation of incoming stimuli by higher order cortical centers. Alternately, early stimulus representation could be shaped by previous experience, thus providing a biased yet relevant interpretation of incoming stimuli. This study examines the activity of output cells, mitral cells, from the first stage of odor information processing in the olfactory bulb during an odor discrimination task. We found that odor responses changed during the task in a manner that increased the ability of the circuit to convey information necessary to discriminate among closely related odors. A switch between which of the two odors were rewarded caused mitral cells to switch the polarity of their divergent responses in behaviorally relevant ways. These results show that early neural representations of odor can be shaped by previously derived meaning, providing a simplified yet biased interpretation of the odor environment to higher cortical structures.

          Abstract

          Early neural representation of odor can be shaped by previously derived meaning, providing a simplified yet biased interpretation of the odor environment to higher cortical structures.

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          Most cited references 75

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          Unsupervised spike detection and sorting with wavelets and superparamagnetic clustering.

          This study introduces a new method for detecting and sorting spikes from multiunit recordings. The method combines the wavelet transform, which localizes distinctive spike features, with superparamagnetic clustering, which allows automatic classification of the data without assumptions such as low variance or gaussian distributions. Moreover, an improved method for setting amplitude thresholds for spike detection is proposed. We describe several criteria for implementation that render the algorithm unsupervised and fast. The algorithm is compared to other conventional methods using several simulated data sets whose characteristics closely resemble those of in vivo recordings. For these data sets, we found that the proposed algorithm outperformed conventional methods.
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            Combinatorial receptor codes for odors.

            The discriminatory capacity of the mammalian olfactory system is such that thousands of volatile chemicals are perceived as having distinct odors. Here we used a combination of calcium imaging and single-cell RT-PCR to identify odorant receptors (ORs) for odorants with related structures but varied odors. We found that one OR recognizes multiple odorants and that one odorant is recognized by multiple ORs, but that different odorants are recognized by different combinations of ORs. Thus, the olfactory system uses a combinatorial receptor coding scheme to encode odor identities. Our studies also indicate that slight alterations in an odorant, or a change in its concentration, can change its "code," potentially explaining how such changes can alter perceived odor quality.
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              A novel multigene family may encode odorant receptors: a molecular basis for odor recognition.

              The mammalian olfactory system can recognize and discriminate a large number of different odorant molecules. The detection of chemically distinct odorants presumably results from the association of odorous ligands with specific receptors on olfactory sensory neurons. To address the problem of olfactory perception at a molecular level, we have cloned and characterized 18 different members of an extremely large multigene family that encodes seven transmembrane domain proteins whose expression is restricted to the olfactory epithelium. The members of this novel gene family are likely to encode a diverse family of odorant receptors.
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                Author and article information

                Contributors
                Role: Academic Editor
                Journal
                PLoS Biol
                pbio
                plbi
                plosbiol
                PLoS Biology
                Public Library of Science (San Francisco, USA )
                1544-9173
                1545-7885
                October 2008
                28 October 2008
                : 6
                : 10
                Affiliations
                Department of Cell and Developmental Biology, Neuroscience Program and Rocky Mountain Taste and Smell Center, University of Colorado Denver Anschutz Medical Campus, Aurora, Colorado, United States of America
                University of Maryland, United States of America
                Author notes
                * To whom correspondence should be addressed. E-mail: diego.restrepo@ 123456uchsc.edu
                Article
                08-PLBI-RA-1962R2 plbi-06-10-11
                10.1371/journal.pbio.0060258
                2573932
                18959481
                Copyright: © 2008 Doucette and Restrepo. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
                Page count
                Pages: 20
                Categories
                Research Article
                Neuroscience
                Custom metadata
                Doucette W, Restrepo D (2008) Profound context-dependent plasticity of mitral cell responses in olfactory bulb. PLoS Biol 6(10): e258. doi: 10.1371/journal.pbio.0060258

                Life sciences

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