Abstract
1. The electrical responses obtained at various levels of the olfactory pathway when the nose of the himé salmon, a landlocked Pacific salmon, Oncorhynchus nerka, was infused with an odorous solution, were analyzed in terms of the frequency components by means of active band-pass filters.
2. The responses of the olfactory nerve appeared over a wide frequency range (20-315 Hz, the major frequency component being 40-125 Hz). It was composed of two kinds of frequency components, i.e., the 20-125 Hz components, which did not adapt during the stimulation, and the 125-315 Hz components, which adapted rapidly.
3. The responses in various regions of the olfactory bulb appearing in a narrower and lower frequency range (3.15-20 Hz, the major frequency component being 5-8 Hz) were compared with those from the olfactory nerve. They consisted of two kinds of frequency components, i.e., the 3.15-5 Hz components, which did not adapt during the stimulation, and the 5-20 Hz components, which adapted rapidly.
4. The responses in various regions of the olfactory lobe were almost identical with those of the olfactory bulb.
5. The activities in the 5-12.5 Hz frequency components were also seen in the responses obtained from both the olfactory lobe and the olfactory bulb on the contralateral side.
6. It is suggested that an asynchronous firing of the olfactory nerve fibers is largely converted to a synchronous one at the levels of the olfactory bulb.
7. The signal propagation through the olfactory pathway and the controlling mechanism of olfactory adaptation are discussed.
