74 DAVID G. MOULTON 



duration. The most active responses were generally obtained from 

 electrodes directed into the cribriform plate from the bulbar side, and, 

 as can be seen in Fig. 4, they ocurred whenever spike discharges in response 

 to odor appeared in the bulb. The stimulus-response curves for the two 

 types of activity cover similar intensity ranges and both responded to 

 4.39 log M amyl acetate (Figs. 10 and 11). 



filtered air 



/"^ 



eogenol lOm.sec |50pV 



Fig. 3. Activity recorded from electrodes directed into the cribriform plate 

 through which pass the primary olfactory neurones. When the undisturbed 

 animal is breathing filtered air there is a higher discharge than that seen in Fig. 2 



(top trace) 



Filtered air 



b pmmmmmmmmmmmmmmammmmmmmmmim 



Amy! acetate 



1 sec 



Fig. 4. Activity derived from the same site as were the records in Fig. 2 (but at 

 slower film speed), compared with bulbar spike potentials recorded simultan- 

 eously, (a) periphery, (b) bulb. 



In one animal a spectrum of slow and fast fiber activity was recorded 

 from electrodes chronically implanted under direct visual control into the 

 ethmoidal nerve as it enters the cribriform plate. Odor stimulation was 

 generally followed by a rapid increase of summated activity to a steady 

 state, more stable, and with a different pattern than that shown by the 

 bulbar spike discharges. In particular the marked after-discharges which 

 sometimes appear in the bulb were seldom reflected in the activity of this 

 nerve (Fig. 7). 



Wave Activity of the Bulb 



When an undisturbed rabbit was breathing filtered air, low amplitude 

 asynchronous waves sometimes showing frequencies in the range of 



