ELECTRICAL ACTIVITY IN THE OLFACTORY SYSTEM 75 



75-90 cps, could be recorded from the bulb. Those gave way to flares of 

 high amplitude almost sinusoidal waves most commonly appearing with 

 each inspiration, when an odor was presented (Fig. 5). In each flare, two 

 or three components can often be distinguished : an initial burst in the 

 range 75-85 cps, the main train of high amplitude waves about 50-70 cps, 

 and a final phase of lower amplitude waves about 40-50 cps. While other 

 frequencies were also recorded from the bulb, (7, 10-14, 20-28 cps), the 

 50-70 cps rhythm is the most characteristic. Disconformity of wave and 

 spike discharges was frequent — isolated flares appearing when a decline, 

 or little or no change in the level of the spike discharges was apparent. A 

 discrepancy of this kind was also observed when the rabbit was under 

 light nembutal anaesthesia (Fig. 8). Conversely, the period of maximum 

 spike responses to an odorant may coincide with a temporary disappearance 

 of the wave flares. This evidence suggests that the wave and spike activity 

 is generated by different structures. 



I\ A /\ A 



0-2 mV 



01 sec 



Fig. 5. Two wave flares from the bulb. The main and terminal phase of each 

 flare often show different frequencies. Tiius in one animal deer music evoked a 

 main phase of about 60 cps and a terminal phase of 50-60 cps, while coyote 

 urine elicited a main phase of 70 cps, and a terminal flare of 40-45 cps. An 

 initial phase of 75-85 cps is less often distinguishable. 



Bulbar Spike Potentials 



A continuous irregular discharge of spikes is normally present in the 

 bulb when an undisturbed rabbit is breathing filtered air. What happens 

 when an odor is introduced depends, at least partly, on the type and 

 concentration of the odor, on the frequency with which the animal has 

 been previously exposed to it, and on placement — a common pattern 

 being that shown in Fig. 6. Here the spikes become grouped with each 

 inspiration, but in the interburst intervals there is a pause in the rate of 

 firing, which may carry activity to a level below that of the resting discharge. 



Such a pattern seldom summates eff'ectively against the fluctuating 

 baseline, even although counter records may indicate a marked increase 

 in the frequency of high amplitude spikes. Novel odorants (i.e. odorants 

 which had not previously been presented to the animal) evoked the most 

 prominent spike discharges (Fig. 7), but their eff*ectiveness generally declined 

 with repetition and no consistent relation between the amplitude of the 

 summated response and the baseline for any concentrations of the odorant 

 tested could be estabUshed. The time of appearance of the response 



