R. HERNANDEZ-PEON AND H. BRUST-CARMONA 



411 



for 5 months without the least success: the animal revealed itselt completely 

 unable to perform the required task. In contrast, simpler associations were obtained 

 very quickly (with an almost normal score) : generalized movements then orienta- 

 tion towards the food tray at the signal. 



This might indicate, if still necessary, that, depending upon the complexity of 

 the training performance, the nervous structures to miplicate as a site for the link 

 mav be different. It is perhaps significant that, in our observation, the mesence- 

 plialic reticular formation was apparently intact and that at the same time the 

 ability for elementary conditioning, but not for a complex one, was preserved. 



CAT 14 



Fig. 4 

 Summary of lesions destroying the mesencephalic reticular system. (From Doty, R. W., 

 Beck, E. C. and Kooi, K. A., 1959. Effect of brain stem lesions on conditioned responses of 

 cats. Experiineiitiil Neurology, I, 360.) 



Segundo. Concerning lesion effects on conditioned responses, I would like to 

 add observations made by our group. Small lesions in mesencephalic reticular 

 formation or amygdaloid complex or large lesions in lateral nuclear complex of 

 thalamus (involving lateral and medial geniculate and V.P.) did not produce 

 marked perturbations in learned or learning abilities. A lesion that destroyed the 

 centre-median provoked less of a response learned previously. A comparable loss 

 was encountered after a large lesion of the head of the caudate nucleus in one cat 

 but, contrastingly, another cat with a similar lesion was not perturbed: hence the 

 caudate nucleus gave ambiguous results (as it did in the self-stimulating studies 

 mentioned by Dr Olds) (Roig, Segundo, Sommer-Smith and Galeano, I959; 

 Segundo, Roig and Sommer-Smith, 1959). 



When lesion effects upon conditioning are discussed, the learned effect should 

 be identified since it is conceivable that one same lesion mav affect different 



