ELECTRICAL ACTIVITY IN THE OLFACTORY SYSTEM 83 



show responses to odor, which, when summated, are virtually indistin- 

 guishable from peripheral activity. In this condition relatively consistent 

 responses to odor occur and a quantitative analysis of both peripheral 

 and bulbar spike discharges becomes possible. 



Before considering the possible causes of this effect it is convenient to 

 distinguish two levels of resting discharge : a primary level of low ampli- 

 tude stable activity seen in deeply anaesthetized animals, and a secondary 

 level of higher amplitude irregular spike discharges which appear in 

 unanaesthetized or lightly anaesthetized animals. Examination of Fig. 8 

 suggests that the secondary level of resting discharge is absent or reduced 

 on the side of the lesion, leaving mainly a low amplitude, stable activity 

 comparable to the primary resting discharge. On the opposite side, 

 however, the fluctuating secondary activity still appears to be present, 

 although some reduction may have occurred. Thus, although the spikes 

 elicited by odor are of similar amplitude in both bulbs, those on the side 

 of the lesion stand out more clearly than those on the opposite side, which 

 are embedded in the secondary resting discharge. 



Such evidence suggests that activity in the eff'erent fiber systems may 

 normally activate the secondary resting discharge, possibly adjusting it to 

 a level appropriate to the biological significance of the afferent inflow to 

 the bulb. However, the possibility that some enhancement of the induced 

 spikes may also occur cannot be ruled out on the basis of available evidence. 



Similarly there is insufficient evidence to allow any generahzations about 

 the relative effectiveness of different odorants in stimulating various points 

 in the bulb or the periphery in this preparation, but the existence of 

 temporal and spatial patterning of responses to different odors, previously 

 demonstrated by Adrian (1956) and Mozell and Pfaffman (1954), is 

 apparent. 



SUMMARY 



The electrical responses of the olfactory bulbs and peripheral olfactory 

 system to odor stimulation were explored in rabbits with chronically 

 implanted electrodes. There were marked disconformities between the 

 behavior of the spike and wave activity of the bulb, and for a given stimulus 

 the spike response did not summate effectively or consistently against the 

 fluctuating high amplitude resting discharge present in the unanaesthetized 

 animal. The variability was greatly reduced by a unilateral lesion in 

 the anterior olfactory areas through which pass the efferent fibers to the 

 bulb. In such a preparation bulbar spike responses on the side of the 

 lesion especially stood out against a stable low amplitude resting discharge, 

 and they summated effectively and consistently. Repeated presentations 

 of the same olfactory stimulus led to no diminution (habituation) of 



