1 92 Information Storage and Neural Control 



conditioned DC shift was also restricted to the previously stimu- 

 lated hemisphere although the tone was presented to both ears 

 equally in open field conditions. 



In addition to such direct conditioning of a cerebral electrical 

 event, the increasing availability of DC amplifiers made it possible 

 for Rusinov (49) and, more recently, Rowland (47) to identify 

 steady potential shifts occurring regularly in the course of classical 

 behavioral training. Rusinov (48) also discovered a most intriguing 

 behavioral eff'ect when low-level surface positive polarizing cur- 

 rents were applied to a part of the motor cortex. The current levels 

 employed were sub-threshold with respect to direct production 

 of limb movement. But during the period of current flow (and 

 for some minutes afterward) any ambient sound, light or touch 

 would produce the limb movement to be expected from adequate 

 (supra-threshold) stimulation of the motor area to which the 

 current was applied. Rusinov felt that the anodal polarization 

 produced a "dominant focus" of excitation which facilitated the 

 development of a temporary connection between, for example, 

 the auditory and motor systems. 



We have been able to confirm the Rusinov experiment in our 

 own laboratory and, in addition, have made some observations 

 on the activity of single nerve cells in such polarized regions (40). 

 Single cells in motor cortex did not respond to acoustic stimulation 

 before polarization (Fig. 3A). During the passage of anodal cur- 

 rent (10 microamps) cells of several different types (Figs. 3B, C 

 and D) were easily triggered by the same acoustic signal. Since 

 we were interested in mechanisms for information storage we per- 

 formed the experiment in a slightly diff'erent way, a way which 

 allowed observation of a selective sensitivity with respect to signals 

 differing in their history of exposure to polarizing current. A group 

 of stimuli was chosen and all members of the group were presented 

 repeatedly to the animal until habituation (as judged by lack of 

 behavioral or EEG response) was complete. A polarizing electrode 

 together with a fine microelectrodewas placed on the motor cortex 

 and the current was turned on. One member of the previously 

 habituated stimulus group was selected (in this case a 200 cycle 

 per second tone) and was presented to the animal about thirty 

 times in the course of forty-five minutes. A burst of unit activity 



