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 todifferent odorants have been presented and discussed with referenceto homologous properties of olfactory receptor cells. This paperdeals with further mathematical processings of part (experimentA) of these original data and proposes a comparison with a similarstudy performed in receptor cells, using the same odorants presentedat the same concentrations. In the olfactory bulb the patternof similarities and differences among odorants was found tobe almost the same whether the mathematical processings wereapplied to the odor-evoked discharge frequencies or to excitatoryresponses considered separately. By contrast, separate processingof inhibitory responses led to a different organization of odorantsimilarities, indicating that inhibitory responses were lessdiscriminating than excitatory responses. This was discussedin relation to the synaptic organization of the olfactory bulb.The comparison of these findings with those previously obtainedin receptor cells showed indisputable resemblances between thepatterns of discrimination among odorants at both levels ofthe olfactory pathways, especially in the grouping of some odorantsin pairs and in the overall organization of the olfactory spaceas determined by factor analysis. The findings also suggestedthat odorant discrimination was slightly improved in the olfactorybulb but no sign of a novel, specific odour categorization couldbe found.