258 BRAIN MECHANISMS AND LEARNING 



from several inicroclcctrodcs and will bear with us in these early faltering steps. 

 The results must be viewed as only first order approximations since adequate 

 statistical analysis awaits the accumulation of more data with the use of multiple 

 microelectrodes concurrently sampling the same cellular population. 



As soon as conditioning trials were begun, it was obvious that there was wide 



STAGE III 



Vis. Cortex 



'"******"^^''wfTP(WiflM||PI|Pf|^^ 



ucs 



cs 



Vent. Ant. -h.,^.. .... ^U.., . ..,,^,v'^^f^>^^V>w. wt|f^f^^ 



UCS 



CS 



Mes. Ret. 



Fig. 7 



Pattern of response during Stage III of the conditioning procedure. (See text for further 



explanation.) Cahbration: 250 msec. 



variation in the pattern of unit discharge to both conditioned and unconditioned 

 stimuli. This was true even of different but adjacent units in the same ganglionic 

 grouping within any given stage of the conditioning procedure. For this reason 

 the results to be demonstrated can be considered valid only in a rough statistical 

 sense. For example, we define 'increased firing' as meaning that more than 50 per 



