THE DEPENDENCY OF THE OLFACTORY NERVE DISCHARGE UPON SNIFF VOLUME, SNIFF DURATION AND NUMBER OF MOLECULES WITHIN A SNIFF (FROG, BULLFROG)

The summated multiunit olfactory nerve discharge was recorded in response to precisely defined artificial sniffs of n-octane and the purpose of investigating the effects of simulation variables upon the magnitude of the olfactory response in the bullfrog (Rana catesbeiana). It was found that when the flow rate of the sniff (F) and the number of odorant molecules within the sniff (N) were held constant, the size of the response did not change in spite of altering the volume of the sniff (V) and the duration of the sniff (T) 8-fold. When delivery rate (D) and V were held constant, while N and T increased 8-fold, the Log(,2) response increased dramatically as a linear function of log(,2) N or T. When concentration (C) and T were held constant, the log(,2) response also increased in an approximately linear function of log(,2) N or V, but with a smaller slope. Nearly identical results were observed when the recording site was moved from the medial to the lateral aspect of the olfactory nerve. A raised perisniff flow of humidified air was found to alter the relative effects of the sniff variables very little. On the other hand, a perisniff flow of humidified air which was decreased to zero had a greater impact on the relative effects of the stimulation variables than any other perisniff flow condition. The zero perisniff flow rate also produced responses which were twice as large as in the other conditions. The results are discussed in terms of their support for a multiplicative 3-variable model relating the primary variables (N, V and T) to the magnitude of the olfactory response. In addition, the ability of the derived variables (C, D and F) and yet unnamed derived variables to account for the combined effects of primary variables is also addressed. The results are discussed in their relationship to psychophysical temporal summation.