WAVELET ANALYSIS OF OLFACTORY NERVE RESPONSE TO STIMULUS

Multiunit electrophysiological activity recorded by gross electrodes f rom the olfactory nerve was analyzed by wavelet decomposition, a relat ively new method of signal processing. The analysis was run on data fr om the unstimulated olfactory system as well as on data evoked in resp onse to six different odorant stimuli. Like Fourier analysis, wavelet analysis provides a spectral decomposition of the signal. Unlike Fouri er, wavelet analysis also locates the dominant spectral features in ti me. The output of a wavelet analysis can be further processed to enhan ce selected features. The increased amplitude of the nerve response ev oked by stimulation was the most obvious feature, but efforts to learn from it were unproductive. The temporal pattern of receptor cell acti vity was much more yielding. The analysis resolved the nerve activity into three classes of events based on duration. On wavelet maps these classes of events separate out into three shifting and overlapping but distinct bands, one of which was interpreted as being associated with individual receptor cell firings and the other two as short and somew hat longer duration bursts of activity that was attributed to the sync hronized firing of a group of receptor cells. This interpretation is s upported by experiments in which waveforms simulating action potential s and bursts of action potentials are added to recorded data. Stimulat ion of the olfactory system with odorant molecules evokes a significan t increase in the number of short duration bursts, and an amplitude in crease that can be related to the number of receptor cells responding. Changes in the patterns of wavelet events can be associated with sync hrony of cell firing, reset times for bursts of firing, and possibly o ther physiological dynamics. A number of differences in activity patte rns with different odorants were observed, but without sufficient repe atability to allow reliable discrimination among them. While this stud y is clearly preliminary in that regard, it shows the potential of the wavelet method for contributing to the understanding of olfaction. (C ) 1995 Academic Press Limited