E. GRASTYAN 25I 



Unfortunately we have very little and incomplete information about 

 the importance of the diffuse thalamic projection system in the elaboration 

 of the startle response and orientation reflex. Recently Eidelberg (1959) 

 made an important observation that a lesion of the centrum medianuni 

 irreversibly eliminates the possibility of eliciting the hippocampal rhyth- 

 mic slow^ potentials. According to this observation the role of the thalamus 

 is crucial in the control of hippocampal function. Unfortunately, no direct 

 observations arc available concerning the effects of this lesion on the 

 startle response and orientation reflex. 



The greatest difficulty is found at the present time in understanding the 

 mechanism responsible for the transition of the startle response to the 

 orientation reflex and the orientation reflex to the proper conditioned 

 reflex. When we consider that the most dramatic electrical changes during 

 this period of time can be observed in the hippocampus, it seems vcrv 

 probable that the solution to these questions is more or less identical with 

 the understanding of the generation of the hippocampal slow potentials. 



In reviewing the above facts my first intention was to demonstrate the 

 highly complex nature of the manifestations preceding the establishment 

 of the most simple conditioned reflex. I am convinced that for the 

 approach to the neural mechanisms of conditioning, an inescapable 

 requirement would appear to be the breakdown of the learning process 

 into its most elementary components, as was necessary in research on the 

 spinal cord. That is the only way in which we may secure a more exact 

 correlation between electrical and behavioural phenomena. 



GROUP DISCUSSION 



MoRRELL. Dr Fcssard has asked nic to begin the discussion ot Dr Grastyaia's 

 report and to present some ot the material partially reported at the Moscow 

 symposium and which has not \et appeared in print. Some of this material agrees 

 beautituUy with that now before us and may serve to underscore the lack of 

 behavioural correlation with some clcctrographic criteria of conditioning and 

 perhaps indicate in some measure why this is so. In addition I think we can illustrate 

 some features ot hippocampal participation in the conditioning process. 



As Dr Grastyan has so well pointed out, it has been dirticult to assign specific 

 excitatory or inhibitorv connotations (with reference to cell discharge) to the 

 electrical activity recorded with large electrodes from various ganglionic regions. 

 This is perhaps one ot the more important reasons for the great ambiguity in 

 relating the previously discovered electrical signs o( conditioning to any aspect of 

 behavioural learning. Causallv related interactions between various levels of the 

 central nervous system as well as the degree of participation of these elements in 

 the total integrated response are probablv better expressed as changes in a rate of 

 unit discharge than in terms of the slow oscillations reflecting dendritic polariza- 

 tions. Because the latter may be non-propagated, they are perhaps less likely to 



