Information Storage in Nerve Cells 201 



Now it may be legitimate to question the pertinence of these 

 examples of cellular memory or the potential gradients with which 

 they are associated to anything resembling" a functional memory 

 in the behaving animal or man. Nevertheless, these considerations 

 have led to a direct test of the hypothesis that manipulation of 

 the cortical steady potential might alter a learned response. 

 Particular attention was paid to the sign and orientation of the 

 electrical field and to behavioral evidence bearing upon a dis- 

 tinction between learning and memory. 



Twelve mature male rabbits weighing between two and three 

 kilograms were used. Prior to training, the animals were operated 

 upon under nembutal anesthesia with sterile precautions for im- 

 plantation of six stainless steel epidural electrodes. In addition, 

 nylon plugs were inserted bilaterally over motor (both fore limb 

 areas) and visual cortex. 



Beginning no earlier than one week after surgery, the animals 

 were trained to perform a conditioned avoidance response which 

 involved lifting of the right forelimb. The unconditional stimulus 

 (UCS) was an electric shock (sixty per second square waves) of a 

 voltage just sufficient to cause unconditional limb withdrawal on 

 all stimulus applications. Stimuli were delivered through needle 

 electrodes in the foot pad. The conditional stimulus (CS) was a 

 flickering light at eight to ten flashes per second from a Grass 

 stroboscope placed ten inches in front of the animal at eye level. 

 Stimuli were presented by hand and the UCS was omitted if the 

 animal responded by flexion of the appropriate limb within 1.5 

 seconds after flicker was turned on. The animals were trained to 

 a level of 70-75 per cent correct responses in twenty trials before 

 polarization was begun. The low level of performance was chosen 

 intentionally in the hope that we might be able to observe enhance- 

 ment of conditioning as well as depression secondary to polarization. 



Capillary pore electrodes (saline bridge and silver-silver chloride) 

 were placed in the nylon plugs for polarization. A constant current 

 stimulator having a high source resistance was used. Current was 

 continuously monitored and maintained at about 10 microamps per 

 square millimeter. Pore diameter in the visual cortex was 5 milli- 

 meters, thus covering more than half of the visual cortex on each 

 side. Pore diameter in motor cortex was 2 millimeters. Current 



