254 BRAIN MECHANISMS AND LEARNING 



localized dcsynchronization characteristic of Stage III. The latter cannot be clearly 

 seen in this figure because the gain has been greatly reduced in order to avoid 

 blocking of the amplifiers in a tape recorder ted through the EEG machine by the 

 high voltage transients. 



INITIAL PRESENTATION 



Vis. Cortex %*«^*^ **^JPr • 



ucs 



cs 



Vent. Ant. . , . 



UCS 



cs 



Mes. Ret. 



UCS 



cs 



Hippocampus 



CS 



Fig. 3 

 Simultaneous microelectrode records from the cortex and subcortical regions in a cat during 

 clectroccrebral conditioning. Onset of the conditioned stimulus (tone 500 cycles per second) 

 is indicated by the first widening of the signal channel. Onset of the unconditioned stimulus 

 (intermittent light 10 per second) is indicated by the second widening of the signal channel. 

 This convention applies to all the microelectrode figures. The derivations also apply to the 

 same figures and they are all tracings from the same animal. 



In the light of Dr Grastyan's comment that the slow rhythms in the hippocampus 

 may be caused to reappear by a change in the stimulus situation after they have 

 disappeared, I might add that we have observed a similar phenomenon with 

 respect to the slow waves wliich constitute the Stage II response. If, during Stage 



