654 BRAIN MECHANISMS AND LEARNING 



conditioned reflexes play a very great role in higher nervous activity because they 

 constitute a background for the phasic conditioned reflex activity and provide for 

 it a functionally steady basis. In other words, I imagine the relations betw^een these 

 two types of conditioned reflexes similar to those well-known relations which 

 exist between tonic and phasic unconditioned reflexes and which were so excel- 

 lently investigated by Sherrington, Magnus and others. 



Hernandez-Peon. I agree completely with the view expressed by Dr Konorski 

 who points out very clearly that all the levels of the central nervous system parti- 

 cipate in learning and, of course, each level participates in different tvpcs of 

 learning. I should like also to add to this general discussion that in the absence, 

 however, of certain parts of the brain some other part may take over the function 

 of the absent part. This phenomenon has been known for a long time and has been 

 called 'neural equivalence'. Therefore, in designing experiments for testing the 

 function of a given part of the brain we must consider scparatclv the immediate 

 and the late effects of the lesion. 



Segundo. The hypothesis can be advanced th.it a degree of freedom exists 

 which enables different individuals or even the same individual under different 

 circumstances to learn one specific task utilizing different regions or systems in the 

 brain. No direct proof of this is as yet available but such a possibility would agree 

 with the following observations, (i) Interference (by destruction or excitation) with 

 a given neural structure may affect learned behaviour in different or even contradic- 

 tory manners. At the level of the caudate nucleus for instance, lesions abolished a 

 conditioned response in certain preparations but did not affect it in others (Galeano, 

 Roig, Segundo and Sommcr-Smith, in preparation) and stimulation effects were 

 conflicting (Olds, this volume). Tliis could indicate that, in different preparations, 

 the same structure participated differently in production of the same reaction, (ii) In 

 many instances, cerebral mutilation has provoked loss of a learned ability that was 

 re-established by subsequent training. Participation of the destroyed structure 

 obviously was necessary initialK' but, since re-learning was possible, the same 

 necessary role must have been assumed by a different nucleus. 



Thorpe. I agree with what Dr Segundo has just said. It seems that an animal can 

 learn the same thing simultaneously in two or more different structures in the 

 central nervous svstem. In this connection, the case of the animals reared under 

 imperfect conditions and so not of normal health, is of special interest. Sometimes 

 such animals cannot pertorm certain activities normalh^ regarded as 'instinctive' 

 without practice or experience, but can nevertheless learn them very rapidly. It 

 may be that the process which results in the completion of the innate behaviour 

 pattern by learning takes place in the same locus, but I think it is very likely that it 

 takes place in a different locus and that would perhaps be a similar instance to that 

 Dr Segundo had in mind: the same pattern being acquired by two different 

 nervous structures. 



Myers. An oft-mentioned argument should perhaps be added here to supple- 

 ment Dr Segundo's and Dr Thorpe's discussion. Behavioural test situations given 



