Odour discrimination by olfactory bulb neurons: statistical analysis of electrophysiological responses and comparison with odour discrimination by receptor cells

Electrophysiological responses of olfactory bulb neurons to different odorants have been presented and discussed with reference to homologous properties of olfactory receptor cells. This paper deals with further mathematical processings of part (experiment A) of these original data and proposes a comparison with a similar study performed in receptor cells, using the same odorants presented at the same concentrations. In the olfactory bulb the pattern of similarities and differences among odorants was found to be almost the same whether the mathematical processings were applied to the odor-evoked discharge frequencies or to excitatory responses considered separately. By contrast, separate processing of inhibitory responses led to a different organization of odorant similarities, indicating that inhibitory responses were less discriminating than excitatory responses. This was discussed in relation to the synaptic organization of the olfactory bulb. The comparison of these findings with those previously obtained in receptor cells showed indisputable resemblances between the patterns of discrimination among odorants at both levels of the olfactory pathways, especially in the grouping of some odorants in pairs and in the overall organization of the olfactory space as determined by factor analysis. The findings also suggested that odorant discrimination was slightly improved in the olfactory bulb but no sign of a novel, specific odour categorization could be found.