210 Information Storage and Neural Control 



term information storage. Despite these brief and uncertain insights, 

 it is most tantaUzing to realize that even at the single unit level 

 of analysis the nature of the neural code has still strangely escaped 

 detection. Thus in Figure 5D the segment of record preceding 

 the application of the single test flash revealed no trace of the 

 information which the subsequent stimulus demonstrated had 

 been retained in that particular cell. This negative evidence argues 

 against the notion that the short-term memory trace is preserved 

 by means of nerve impulses continuously circulating in more or 

 less closed neuronal chains. The recording systems employed 

 should have been adequate to discern such activity had it been 

 present. Perhaps the relevant electrical signs are more likely to 

 be found in tlie slow local oscillations of synaptic potential or 

 other sources of slowly varying voltage. Such oscillation would 

 have been missed by the short time-constant recording system. 

 It is also possible, of course, that the encoding process took place 

 in cells penultimate to the one monitored. 



I should now like to leave the question of electrical mechanisms 

 for information storage in the nervous system and turn to some 

 other approaches which have recently gained prominence. 



While it seems reasonable to postulate an electrical basis for 

 the labile short-term storage mechanism, it is certainly difficult 

 to assume that the relatively permanent memory trace which 

 remains undisturbed by the drastic perturbations of cerebral 

 function produced by convulsions, electro-shock, concussion, or 

 anesthesia so deep as to cause electrical silence, can be based 

 upon continuously circulating nerve impulses (6, 41). Most 

 workers, therefore, have tended to think more in terms of morplio- 

 logical or chemical alterations. The essential thesis argues that 

 recurrent impulse impingement or synaptic bombardment results 

 in a durable morphological or chemical change which renders 

 tliat particular junction or cell more easily susceptible to subse- 

 quent activation via the same pathway. 



Recently hypotheses implicating ribonucleic acid (RNA) in the 

 molecular organization responsible for long-term information 

 storage have been proposed quite independently by a number of 

 workers (14, 26, 27, 29, 30, 32, 39, 43). To my knowledge the first 

 statement of this general hypothesis in the English literature was 



