244 BRAIN MECHANISMS AND LEARNING 



The observations to be reviewed were made on cats with chronically 

 implanted electrodes during the elaboration of conditioned alimentary 

 and avoidance responses. By means of a careful analysis of the motion 

 pictures taken synchronously with the electrical recordings, it was 

 established that the orientation reflex was invariably accompanied by a 

 series of characteristic slow potentials (4-7 c/s) in the hippocampus and in 

 some points of the reticular formation. Attention to this reaction as a 

 peculiar kind of archicortical arousal was directed by Green and Arduini 

 (1954). According to our observations, this theta activity was an excellent 

 indicator of the orientation reflex, since it invariably and synchronously 

 appeared with the orientation, irrespective of whether it manifested itself 

 spontaneously or was elicited by a conditioned stimulus. 



So far these observations do not represent any contradiction of the 

 classic conception. Later, however, a careful analysis of the electrical 

 recordings disclosed a challenging fact. It turned out that unfamiliar 

 stimuli, even at their first application, elicited neither the hippocampal 

 slow potentials nor behavioural orientation in the great majority of the 

 cases. The unfamiliar stimuli elicited in these cases a desynchronization in 

 the hippocampus quite similar to that in the neocortex. The characteristic 

 slow potentials did not appear until after several presentations of the 

 stimulus to be conditioned, and were also accompanied by typical 

 orienting and searching movements. 



From these consistent observations we were compelled to conclude that 

 the orientation reflex cannot be an unconditioned phenomenon but must 

 be an extremely rapidly developing conditioned manifestation. This 

 surprising conclusion seems to be supported by the long known fact that 

 the orientation reflex can be easily extinguished, like conditioned but 

 unlike unconditioned reflexes. 



On the basis of these considerations we have to conclude that for the 

 elicitation of the orientation reflex, the stimulus has to be famihar in a 

 certain measure. I should like to emphasize the attribute of the 'certain 

 measure' since the significance of the conditioned stimulus at the time of 

 appearance of the orientation reflex is still uncertain in the animal. It has 

 some motivational effects, but it does not evoke the proper conditioned 

 reflex yet, or only with a very long latency. In other words the animal 

 performs orientation movements for the very reason that he 'does not 

 know' the exact meaning of the stimulus. (What is it reflex.) 



In perfect agreement with this, it has been observed that at the stage of 

 stabilization of the conditioned reflex, when the conditioned movements 

 become automatic, both the hippocampal slow waves and the orientation 



