Information Storage in Nerve Cells 211 



that of Katz and Halstead in 1950 (30). Most recently in a series 

 of lectures and articles Hyden (26, 27) has forcefully argued for 

 implication of RNA in the molecular mechanism of memory. 

 Although the concrete evidence is sparse, some is now available. 

 Kreps (32, 56) in the Soviet Union, is reported to have demon- 

 strated an alteration in RNA synthesis in regions of the nervous 

 system related to the conditioned stimulus after establishment of 

 the conditioned response. In cats, John, Wenzel and Tschirgi (29) 

 noted that intraventricular injection of ribonuclease was followed 

 l^y deterioration of pattern discrimination lasting" about four days. 

 Avoidance CRs in the same animal were unaffected. Unfortunately 

 no control data were presented with regard to local or general 

 changes in brain RNA content or turnover. Therefore, since other 

 substances such as calcium or potassium ion also reversibly impair 

 CR performance, it is not certain that the disturbance was related 

 to an alteration of the RNA substrate rather than to another more 

 nonspecific action of ribonuclease. 



Our own explorations in this area were derived from an inci- 

 dental observation made in the course of investigation of an 

 entirely separate problem. We had been studying some physio- 

 logical properties of the chronic focal epileptogenic lesion produced 

 in animals by local freezing of a small area of the cortical surface 

 (36). Following this procedure, the gradual establishment of an 

 epileptogenic lesion may be verified by recording the paroxysmal 

 electrical activity which appears in the cortical tissue immediately 

 adjacent to the frozen zone. We were interested in studying the 

 ontogenesis of an epileptic lesion from a chemical as well as an 

 electrical point of view, and among a number of findings was the 

 observation that nerve cells in the area of epileptic discharge 

 stained densely with methyl green pyronin (39). Methyl green 

 pyronin is one of the substances generally used for the histochemical 

 demonstration of RNA. 



It was not particularly surprising to find increased concentra- 

 tions of RNA in cells discharging at abnormally high rates. Hyden 

 and co-workers (4, 5, 20, 21, 22, 23, 25) using much more elegant 

 technicjues had already demonstrated increases in cellular RNA 

 consequent to prolonged stimulation. Recently lizuka et al. (28), 

 in Japan, have confirmed our own observations specifically with 



