the interaction of imposed and inherent olfactory mucosal activity patterns and their composite representation in a mammalian species using voltagesensitive dyes from amphibian data two mechanisms that could underlie the encoding of odorants by the mucosal activity patterns they engender are as follows 1 receptors with similar odorant selectivities could be aggregated spatially on the mucosa inherent patterns 2 in analogy to gas chromatography as odorants are drawn along the surface of the mucosa the strongly sorbed ones could be deposited preferentially upstream whereas the weakly sorbed ones could be distributed more evenly imposed patterns do both of these possible coding mechanisms operate in mammals and if so how do they interact in giving composite patterns imposed inherent fluorescence changes in di4anepps applied to rat mucosas were monitored by a 10 x 10 pixel photodiode array to observe the inherent patterns three odorants of varying sorbabilities first were puffed uniformly onto the entire mucosa mounted in a delrin chamber to bring out the imposed patterns the chamber was then sealed to replicate anatomically the rats nasal cavity and these same odorants were drawn at three flow rates along the mucosal flow path the results demonstrated for the first time the existence of imposed patterns in a mammal the strongly sorbed odorants unlike the weakly sorbed one showed marked imposed patterns within physiological limits increasing the flow rate decreased the magnitude of the imposed patterns one might consider strategies that the olfactory process could use either to negate or to take advantage of the chromatographic effect because the lability of the composite patterns with changing stimulus conditions raises questions about their role in odorant encoding