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Induced waves in the olfactory bulb of the unrestrained cat Moore, Elizabeth Virginia

Abstract

There are some discrepancies in the literature regarding the response of the "induced waves" of the olfactory bulb to odorous stimuli. This work was designed to resolve the controversy by relating the different types of response to alertness of the animal and to concentration of the odour. The envelope of 40 Hz activity from the olfactory bulbs of unanaesthetised cats was recorded on a polygraph, and found to vary with respiration. The animal's nose projected into a stream of clean air to which odorant could be added at different fixed rates for about a minute at intervals. The amplitude of induced wave activity during the stimulus was compared to that shortly before it. Odour concentrations were varied within a 5 x 10⁶ -fold range and the logarithm taken. The alertness of the cat was estimated on a 5-point scale. The data for the middle alertness category were eliminated and those of the two extreme groups subjected to statistical analysis by multiple regression. The percentage change in integrated induced wave activity during stimulus as compared to that during control in a drowsy cat was found to be independent of stimulus concentration and could be in either direction but usually increased. In an aroused cat regression to a third order polynomial was statistically significant (p < 0.02) and accounted for 0.34 of the variability. This result appears surprisingly good in view of the enormous spontaneous variation in the signal and the unreliability of the stimulus, both as to its exact concentration and in the resemblance of its presentation parameters to a square wave. It would be worth while to repeat this study with more animals, more odours and a. better olfactometer design. The shape of the regression was predicted as follows. At low concentrations an alert cat would show an olfactory response in the form of a depression of induced waves. At intermediate concentrations an alarm response would sometimes increase alertness, augmenting the induced waves. At high concentrations the trigeminal-to-autonomic noxious vapour response would intervene, mechanically reducing access of air to olfactory receptors and/ or respiration. A drowsy cat on the other hand might be subject to alerting by any suprathreshold concentration, or could ignore the stimulus with or without perceiving it. Effects of non-olfactory stimuli and spontaneous variations were in fact far more obvious than most of the "olfactory responses".

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