202 Information Storage and Neural Control 



return was effected through a saHne soaked pad held against the 

 palate by the mouth bar of the head holder. Fine needle electrodes 

 were inserted into the forelimb flexors to record the electromyo- 

 gram. The animals were restrained with the head fixed and the 

 limbs free. Figure 10 illustrates the electrical record from one ani- 

 mal at the beginning of the paired trials (Fig. 1 OA) when there was 

 no C;R and later (Fig. lOB) when the ClR was present allowing the 

 animal to avoid the shock. Polarization had not been applied at all. 



These animals were given twenty trials a day every day except 

 for occasional interruptions which may be seen as breaks in the 

 graphs. After achieving the 70-75 per cent criterion polarization 

 was applied (either anodal or cathodal to either motor or visual 

 cortex) throughout the training session on a given day. "Polariza- 

 tion days" and "non-polarization days'' as well as type and site of 

 polarization were distributed randomly within the above criterion 

 limits. As an additional control for possible sensory effects of the 

 constant current, training sessions were carried out during polariza- 

 tion of the ear. 



Figure 11 shows a graph of the learning curve in a typical 

 animal. Per cent correct responses in each day's block of twenty 

 trials is indicated by the points on the graph. The black dots 

 represent days on which no polarization was given. The two inter- 

 ruptions in the graph signify that training sessions were omitted for 

 one or more days. The legend indicates the site of cathodal polari- 

 zation in the six sessions in which it was applied in this animal. 



Cathodal polarization of the ear and of the motor cortex resulted 

 in no apparent change in the "expected" per cent response. 

 Bilateral cathodal polarization of the visual area produced a 

 striking deficit in performance for the entire training session 

 during which the current was applied. Strangely enough the 

 decreased performance was also apparent the following day when 

 training was carried out without polarization. Note, furthermore, 

 that a break in the sequence of daily training sessions of one or 

 more days was almost invariably followed by a prominent deterior- 

 ation in performance (Figs. 11, 12, 13, 14). The latter was charac- 

 teristic of all of these animals under the experimental conditions 

 outlined. The only exception is illustrated in Figure 12A where 

 the first lapse in training of one day was not followed by deterior- 



