E. GRASTYAN 253 



influence other neuronal systems. Our use of niicroelectrodes implanted in 

 cortical and subcortical regions was designed to evaluate relationships in unit 

 discharge characteristics of these structures during the course of a developing 

 conditioned response. 



In previous studies (Morrell and Jasper, 1955; MorrcU, 1957) we have described 

 the historical development of electrocerebral conditioning to combinations of 

 sound and intermittent light as consisting of three stages. The first evidence of 

 conditioning is manitested by a generalized desynchronization produced by the 

 conditioned stimulus in all cortical derivations. Next there is a brief transitory stage 

 when the conditioned stimulus evokes a repetitive response which is at or close to 

 the frequency of the imposed stroboscopic light it that frequency is within the 



Robbit M3 5-1-58 





B 



'"^^'^--^-V 



T Noise 



Fig. 2 



Recurrence of repetitive response in Stage III after adventitious noise. Note that the noise 



itself may elicit rhythmic discharge (B). Cahbration: 200 microvolts and i second. 



range of 3-12 per second. The third stage is characterized by localized desyn- 

 chronization in visual derivations elicited h\ the acoustic conditioned stimulus. 

 Since this discussion was not foreseen, I have not brought adequate illustrations 

 of all of these stages for demonstration. However, some features may be illustrated 

 by examples from a study on cortical conditioning carried out with Dr Barlow 

 and Dr Brazier of the Massachusetts General Hospital and the Massachusetts 

 Institute of Technology. Fig. i provides two bits of pertinent information. If 

 attention is directed to the tracing labelled trial 19, one may see a good example 

 of the repetitive response to an acoustic stimulus. This is the pattern characteristic 

 of Stage II of: the conditioning procedure. In the tracing labelled trial 42 all trace 

 of the conditioned repetitive response has disappeared, to be replaced by the 



