Neuron and stimulus typologies in the rat gustatory system.

Although gustatory neurons may be categorized in terms of one or a few characteristics (e.g. 'best stimulus'), such typologies are essentialistic and inconsistent with modern taxonomic methods. If olythetic taxonomic criteria are used and the variability among neuronal responses is closely analyzed, neuronal 'types' are found to disappear, at least within the acid-salt range. This applies to both the primary nerve level (chorda tympani nerve) and secondary level (nucleus tractus solitarius) of the taste system in the rat. In the same context, taste stimuli may fall into different groups if several very similar stimuli are used (e.g. sodium and lithium salts). This is not surprising, and may depend on the choice of stimulus arrays rather than a differentiation of a few stimulus types by the taste system. Finally, it should be noted that the arguments regarding neuron and stimulus typologies presented here for the taste system are also valid for other sensory systems, although the conclusions may be different.