Olfactory stimulation variables. Which model best predicts the olfactory nerve response?

Mozell et al. (1984. J. Gen. Physiol. 83:233-267) have examined the traditional manner in which olfactory stimulus-response relationships have been addressed. They developed a model that describes the olfactory nerve response as a function of three factors, viz., the number of odorant molecules (N), the stimulus duration (T), and the stimulus volume (V). In addition, two models derived from this three- variable model were also found to predict the response well. These were the [F, N] model involving flow rate (F = V/T) and, ranking closely behind, the [C, T] model involving concentration (C = N/V). A model involving the delivery rate (D = N/T) and volume was found to predict the response poorly. These models imply very different stimulus- response relationships. The present study was designed to assess the validity of this earlier approach by testing specific predictions drawn from each of the models. Because of the excellence of the [F, N] model, one would predict that the response will not change when F and N are held constant in spite of proportional increases in V and T. Similarly, one would predict from the [C, T] model that the response will be constant when C and T are held constant in spite of proportional increases in N and V. Because of the poor showing of the [D, V] model, one would predict changes in the response even when D and V are held constant while N and T are increased proportionately. It was observed that when F and N were held constant, the response was, in fact, constant. When D and V were held constant, the response increased dramatically. When C and T were held constant, there was a statistically significant, but small, change in the response. These results support the approach taken by Mozell et al. (op. cit.) and highlight the applicability of the [F, N] model to peripheral olfactory processing. The results are discussed in terms of their impact on the traditional manner in which olfactory stimulus-response relationships are conceived.