FRANK MORRELL 389 



valid at least for the primary lesion, that the dark cells arc simply partially 

 chromatolyscd neurones. Yet the same sort of cells are seen in the mirror 

 focus, an area which has been untouched by the experimental procedure, 

 the cortex remaining unexposed until the brain itself was removed. 

 Neither can one account for these findings on the basis of retrograde 

 degeneration for such histochcmical changes are not seen contralateral to 

 a simple cortical excision. 



The observation that changes in ribonucleic acid occur in cell popula- 

 tions subjected to continuous synaptic bombardment is not in itself 

 surprising. Hyden and co-workers, using much more elegant techniques 

 (Hyden, 1943; Brattgard and Hyden, 1952) have already demonstrated 

 increases in cellular RNA with various kinds of stimulation (Hambergcr 

 and Hyden, 1949). They have also demonstrated that such changes occur 

 transneuronally (Hamberger and Hyden, 1949a). The intriguing question 

 raised in the present investigation is not the relation of RNA to nerve 

 activity or inactivity, but rather the relationship of RNA to the coding of 

 that information necessary to effectuate permanent alteration of cellular 

 excitability. 



For the moment it seems reasonable to present the working hypothesis 

 that the cells of the mirror focus undergo a structural alteration and that 

 changes in distribution of RNA, perhaps linked with protein or phos- 

 pholipids, form the chemical correlates of this alteration. Snice the cells 

 and cell systems of the mirror focus have been shown to have some of the 

 attributes of learning and of memory, it is perhaps not too far fetched to 

 consider that the complex of ribonucleic acid and protein represents an 

 essential element in the molecular basis of memory. 



ACKNOWLEDGMENT 



I should like to express appreciation to Doctors Kenneth Osterberg and 

 K. L. Chow for help with the histochemical material. 



GROUP DISCUSSION 



Magoun. I wonder it Dr Morrcll plans to profit in his cytochcniical studies from 

 a simpler situation, where the sensitization of denervation can be detected in 

 greater isolation than in the cortex, such as in a post-ganglionic relay in the 

 peripheral autonomic system which Cannon and his associates studied for so many 

 years. Study of the sensitization of a mirror focus in epileptic genesis in the cerebral 

 cortex is one of which Dr French and others have been investigating at Los Angeles. 

 Dr Morrell's results are similar to theirs and since he has made reference to their 



