R. HERNANDEZ-PEON AND H. BRUST-CARMONA 



409 



conditioned respiratory responses 95 per cent of the time. During 1325 post- 

 operative retraining trials in twenty-six sessions over a period of 37 days there was 

 not even a suggestion of a conditioned response (e.g. Fig. 3). 



On the other hand, in another animal an enormous lesion totalHng 113 mm.^ 

 destroying most of the central mesencephalon (Fig. 4) and producing a profound 

 catalepsy for the 21 days of survival did not preclude the appearance of conditioned 

 reflexes. One could not claim the level of conditioned responsiveness was high in 

 this cat, but neither had it been very good pre-operatively (see Doty, Beck and 



_RPC_ 



CAT 15, I6AUG56 



CSI — ■ — — 1 



'^<''\v;^~,-.'vv--^'^'- j:-^^*^ 



EKG 



t'Sl .-. . ' I Sec I jjV. 



Fig. 2 

 EEG taken on the thirty-sixth post-operative day, of cat having lesions shown in Fig. D-6. 

 (ij) lack of response to presentation of CS alone after twenty-six CS-US pairings on this day 

 which brought the total to 1253 pairings since surgery. (/>) the forty-eighth pairing of the 

 same day showing transition to low voltage, fast activity in marginal gyrus to the US but not 

 the CS. (From Doty, R. W., Beck, E. C. and Kooi, K. A., 1959. Effect of brain stem lesions 

 on conditioned responses of cats. E.xpcriiiieiitiil NciiroUii;}', I, 360.) 



Kooi, 1959) and it seems probable that a prolongation of life would have seen a 

 more impressive recovery. The best performance was six flexion CRs m a session 

 of forty-five trials and respiratory CRs were then present 25 per cent of the time. 

 Equally interesting, in view of the importance of the mesencephalic reticular 

 system is electrocortical 'arousal' reactions, in the return of low voltage, fast 

 patterns for long periods in the EEG of this animal and the presence of an 'arousal' 

 reaction accompanying conditioned responses (Fig. D-io). 



Thus, we cannot support the idea that the mesencephalic reticular formation is 

 of any extraordinary importance in this type of conditioning. I am certain that 

 differences in period of survival and other details can account tor this apparent 

 contradiction between the experiments of Dr Hernandez-Peon and ourselves. 



