Odorant-specific spatial patterns in mucosal activity predict perceptual differences among odorants

1. Using operant techniques, rats were trained to differentially report (i.e., identify) the odorants propanol, carvone, citral, propyl acetate, and ethylacetoacetate. After acquisition training, the animals were tested using a 5 x 5 confusion matrix design. The results of the behavioral tests were used to measure the degree of perceptual dissimilarity between any pair of odorants. These dissimilarity measures were then subjected to multidimensional scaling analysis to establish a two-dimensional perceptual odor space for each rat. 2. At the completion of behavioral testing, the fluorescence changes in the dye di-4-ANEPPS were monitored on the rat's nasal septum and medial surface of the turbinates in response to the same odorants. For each mucosal surface a 6.0 x 6.0 mm area was sampled at 100 contiguous sites with a 10 x 10 photodiode array. 3. Formal statistical analysis indicated a highly significant predictive relationship between the relative position of an odorant's mucosal loci of maximal activity or "hot spot" and the relative position of the same odorant in a psychophysically determined perceptual odor space (F = 15.6, P < 0.001). 4. The results of this study suggest for the first time that odorant-induced mucosal activity patterns serve as the substrate for the perception of odorant quality.