524 BRAIN MECHANISMS AND LEARNING 



electrical activity that presumably reflects a profound disorganization of the 

 neurones under the electrodes. Besides this Bures employs another method, the 

 spreading depression technique, which yields an electrical record from the affected 

 brain region that is entirely flat rather than abnormally active. Appropriate use of 

 tliese physiological methods along with the anatomical ideas for disorganizing 

 cortex Dr Chow referred to should give valuable additional information on the 

 brain function in acquisition and retention of learned responses. 



Chow. I have talked about this with Dr Van Harreveld and he told me that in 

 the monkey you cannot produce spreading depression very regularly. 



EccLES. I think Dr Chow is too hard on hmiselt in interpreting this seeming 

 inconsistency between the learning process and the EEC results. What I should like 

 to think happens in the learning process is a simplification in the neural pathways. 

 Originally a great deal of neural activity is concerned, a lot of it of no value to the 

 learning but it is wandering through large areas, giving vou this large depression 

 of the EEC 



Chow. This is very possible. 



MouELL. From the standpoint of electrophysiology the behavioural learning 

 curve must surely be considered a very coarse kind of measure. Even if these 

 variously recorded electrical events are related to learning in some fundamental 

 manner, I would not expect them to follow the same time-course as the learning 

 curve. 



RosvOLD. We have evidence that can substantiate Dr Chow's point that the 

 connections are cortico-cortical. 



Will the monkey learn anything at all during the period of after-discharge ? Dr 

 Chow demonstrated clearly that he could not learn the visual discrimination 

 problem. I am wondering whether the Animal can learn anything at all. 



What was your stimulation technique because we were not able to disturb 

 the retention ot the visual discrimination problem — by strong stimulation in the 

 temporal lobes. 



Chow. I am using bipolar electrodes to stimulate the temporal cortex, and not 

 recording with EEC I only test them when the EEG shows after-discharge 

 bilaterally. They are wire electrodes insulated except at the lip with 3 or 4 mm. 

 separation between electrode tips. The stimulus is 3 ms. square waves 50 cycles per 

 second, for 5 seconds. 



With respect to whether this effect is specific to the task or not i have not looked 

 into the problem. That is a question of functional localization, which is not the 

 purpose of this study. 



BusER. I still believe in electrophysiology as an index of neuronal activity and 

 neuronal activity is the basis of learning. Maybe the test ^•ou are using is not a 

 good one or the process taking place is not uni-directional. Is it more complex than 

 the total behavioural phenomenon you are observing? Did you happen to record 

 evoked potentials to optic stimulation in the temporal region of the monkey, an 

 observation which could be correlated with your results from ablation techniques? 



Chow. I did not make any recording of evoked potentials in the temporal or 

 visual areas of the monkey. 



As to your first question, I think one should pose meaningful questions to be 

 answered by the EEG technique. Just implanting electrodes and recording the 

 EEG to see what happens is not very satisfying. 



