E. GRASTYAN 255 



HI, when the repetitive response had completely disappeared, an extraneous noise 

 is introduced into the experimental room, a prompt reappearance of the condi- 

 tioned repetitive response to the acoustic signal may be observed on the very next 

 conditioning trial (Fig. 2). Indeed the noise itself may elicit some vestige of these 

 slow rhvthms (Fig. 2b). Our repetitive response is derived from cortical rather than 

 hippocampal regions, but it may have a significance similar to that envisaged by 



HABITUATION 



Vis. Ceirtex 



CS 



Vent. Ant. ^(^'^'^\^^^.^^^,^J^'f^^^ 



CS 



Mes. Ret. '^'•■•K^jiM^'^ nT- ^-^- ^-NvV-ArNAv-*^'^-f""^ "t^ ■ 



CS 



Hippocampus 



CS 



Fig. 4 

 Pattern of response after habituation. (See text for further explanation.) 



Dr Grastyan. The relationship of these stages to behavioural learning is not fully 

 understood although there is some evidence that the Stage II repetitive response is 

 not adequate for behavioural transfer (Chow, Dement and John, 1957) while 

 Stage III or localized desynchronization ma}- be correlated with a motor response 

 (Morrell and Jasper, 1956; Gastaut cr al, 1957). 



The initial microelectrode investigation involved a survey of unit discharge in 

 various subcortical nuclei compared with stages in the evolution of the conditioned 



