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Understanding odor information segregation in the olfactory bulb by means of mitral and tufted cells.

Polese D, Martinelli E, Marco S, Di Natale C, Gutierrez-Galvez A - PLoS ONE (2014)

Bottom Line: This capacity to ignore concentration information does not preclude the olfactory system from estimating concentration itself.The results of the experiments were visualized using principal components analysis and analyzed with hierarchical clustering to unveil the structure of the high-dimensional output space.An important conclusion is also that the morphological difference between the principal neurons is not key to achieve odor information segregation.

View Article: PubMed Central - PubMed

Affiliation: Istituto per la Microelettronica e Microsistemi, Consiglio Nazionale delle Ricerche, Roma, Italy.

ABSTRACT
Odor identification is one of the main tasks of the olfactory system. It is performed almost independently from the concentration of the odor providing a robust recognition. This capacity to ignore concentration information does not preclude the olfactory system from estimating concentration itself. Significant experimental evidence has indicated that the olfactory system is able to infer simultaneously odor identity and intensity. However, it is still unclear at what level or levels of the olfactory pathway this segregation of information occurs. In this work, we study whether this odor information segregation is performed at the input stage of the olfactory bulb: the glomerular layer. To this end, we built a detailed neural model of the glomerular layer based on its known anatomical connections and conducted two simulated odor experiments. In the first experiment, the model was exposed to an odor stimulus dataset composed of six different odorants, each one dosed at six different concentrations. In the second experiment, we conducted an odor morphing experiment where a sequence of binary mixtures going from one odor to another through intermediate mixtures was presented to the model. The results of the experiments were visualized using principal components analysis and analyzed with hierarchical clustering to unveil the structure of the high-dimensional output space. Additionally, Fisher's discriminant ratio and Pearson's correlation coefficient were used to quantify odor identity and odor concentration information respectively. Our results showed that the architecture of the glomerular layer was able to mediate the segregation of odor information obtaining output spiking sequences of the principal neurons, namely the mitral and external tufted cells, strongly correlated with odor identity and concentration, respectively. An important conclusion is also that the morphological difference between the principal neurons is not key to achieve odor information segregation.

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Hierarchical clustering of ET cells output in the odor morphing experiment.The hierarchical clustering of ET output patterns show a clear separation between high concentration odors (red lines) and low concentration odors (blue lines). Mixture odors lie within the high concentration cluster but not far from low concentrations. This is consistent with a proper disposition of concentrations since mixtures are formed by two components of concentration factors of 1 multiplied by mixing factor that sum up to 1 in all cases.
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pone-0109716-g007: Hierarchical clustering of ET cells output in the odor morphing experiment.The hierarchical clustering of ET output patterns show a clear separation between high concentration odors (red lines) and low concentration odors (blue lines). Mixture odors lie within the high concentration cluster but not far from low concentrations. This is consistent with a proper disposition of concentrations since mixtures are formed by two components of concentration factors of 1 multiplied by mixing factor that sum up to 1 in all cases.

Mentions: Figures 6 and 7 show the hierarchical clustering obtained for MC outputs and ET outputs respectively. The results show that MCs and ET cells naturally managed to group the data in clusters according to their odor identity and concentration. Specifically, the dendrogram of Figure 6 illustrates how MCs grouped the six pure odorants into six clearly identifiable clusters. Additionally, the binary mixtures are partitioned into the clusters corresponding to the two component odors, demonstrating once again that the MC outputs are highly correlated with the odor identity. Also note that mixtures are not grouped as new odors, but rather as the more abundant odor component in the mixture. This outcome of our study is consistent with the psychophysical experimental results obtained by Uchida et al. [3]. Finally, the morphing series allows us to determine that the MC output to odor mixtures evolve slowly from odor C to odor E. This is clearly observed in Figure 8 where the PCA scores of MC outputs show the transition of the mixtures from the cluster of one odor to the other cluster. This behavior reproduces the experimental results obtained by Khan et al. [32] in rats. Additionally, other groups have performed morphing experiments with either similar [34] or slightly different results [35]. Figure 7, on the other hand, shows that tufted cells separate data into groups according to the odor concentration independently of the odor classes. This behavior is more noticeable when considering the morphing data; in this case, the total concentration of the mixture is kept constant whereas the odor identity progressively changes from odor C to odor E, once again, the ET cells manage to classify the whole set of the morphing data into the same concentration cluster.


Understanding odor information segregation in the olfactory bulb by means of mitral and tufted cells.

Polese D, Martinelli E, Marco S, Di Natale C, Gutierrez-Galvez A - PLoS ONE (2014)

Hierarchical clustering of ET cells output in the odor morphing experiment.The hierarchical clustering of ET output patterns show a clear separation between high concentration odors (red lines) and low concentration odors (blue lines). Mixture odors lie within the high concentration cluster but not far from low concentrations. This is consistent with a proper disposition of concentrations since mixtures are formed by two components of concentration factors of 1 multiplied by mixing factor that sum up to 1 in all cases.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4214673&req=5

pone-0109716-g007: Hierarchical clustering of ET cells output in the odor morphing experiment.The hierarchical clustering of ET output patterns show a clear separation between high concentration odors (red lines) and low concentration odors (blue lines). Mixture odors lie within the high concentration cluster but not far from low concentrations. This is consistent with a proper disposition of concentrations since mixtures are formed by two components of concentration factors of 1 multiplied by mixing factor that sum up to 1 in all cases.
Mentions: Figures 6 and 7 show the hierarchical clustering obtained for MC outputs and ET outputs respectively. The results show that MCs and ET cells naturally managed to group the data in clusters according to their odor identity and concentration. Specifically, the dendrogram of Figure 6 illustrates how MCs grouped the six pure odorants into six clearly identifiable clusters. Additionally, the binary mixtures are partitioned into the clusters corresponding to the two component odors, demonstrating once again that the MC outputs are highly correlated with the odor identity. Also note that mixtures are not grouped as new odors, but rather as the more abundant odor component in the mixture. This outcome of our study is consistent with the psychophysical experimental results obtained by Uchida et al. [3]. Finally, the morphing series allows us to determine that the MC output to odor mixtures evolve slowly from odor C to odor E. This is clearly observed in Figure 8 where the PCA scores of MC outputs show the transition of the mixtures from the cluster of one odor to the other cluster. This behavior reproduces the experimental results obtained by Khan et al. [32] in rats. Additionally, other groups have performed morphing experiments with either similar [34] or slightly different results [35]. Figure 7, on the other hand, shows that tufted cells separate data into groups according to the odor concentration independently of the odor classes. This behavior is more noticeable when considering the morphing data; in this case, the total concentration of the mixture is kept constant whereas the odor identity progressively changes from odor C to odor E, once again, the ET cells manage to classify the whole set of the morphing data into the same concentration cluster.

Bottom Line: This capacity to ignore concentration information does not preclude the olfactory system from estimating concentration itself.The results of the experiments were visualized using principal components analysis and analyzed with hierarchical clustering to unveil the structure of the high-dimensional output space.An important conclusion is also that the morphological difference between the principal neurons is not key to achieve odor information segregation.

View Article: PubMed Central - PubMed

Affiliation: Istituto per la Microelettronica e Microsistemi, Consiglio Nazionale delle Ricerche, Roma, Italy.

ABSTRACT
Odor identification is one of the main tasks of the olfactory system. It is performed almost independently from the concentration of the odor providing a robust recognition. This capacity to ignore concentration information does not preclude the olfactory system from estimating concentration itself. Significant experimental evidence has indicated that the olfactory system is able to infer simultaneously odor identity and intensity. However, it is still unclear at what level or levels of the olfactory pathway this segregation of information occurs. In this work, we study whether this odor information segregation is performed at the input stage of the olfactory bulb: the glomerular layer. To this end, we built a detailed neural model of the glomerular layer based on its known anatomical connections and conducted two simulated odor experiments. In the first experiment, the model was exposed to an odor stimulus dataset composed of six different odorants, each one dosed at six different concentrations. In the second experiment, we conducted an odor morphing experiment where a sequence of binary mixtures going from one odor to another through intermediate mixtures was presented to the model. The results of the experiments were visualized using principal components analysis and analyzed with hierarchical clustering to unveil the structure of the high-dimensional output space. Additionally, Fisher's discriminant ratio and Pearson's correlation coefficient were used to quantify odor identity and odor concentration information respectively. Our results showed that the architecture of the glomerular layer was able to mediate the segregation of odor information obtaining output spiking sequences of the principal neurons, namely the mitral and external tufted cells, strongly correlated with odor identity and concentration, respectively. An important conclusion is also that the morphological difference between the principal neurons is not key to achieve odor information segregation.

Show MeSH
Related in: MedlinePlus