i6o 



BRAIN MECHANISMS AND LEARNING 



tests were given at each of five electric current levels, lo, 20, 30, 40 and 

 50 iJanip. r.m.s. It is believed that the so-namp. stimulus sets up a supra- 

 threshold electric field in the brain of about i-inm. diani. (Olds, i9.vS). 

 The stimulation was divided into ^-second trains separated by ih 

 seconds of no stimulation because it was found that such a discontinuous 



CONTROL 



SERIES 



CINGULATE CORTEX 



Fk;. 7 

 Daily response curves. Slope of black line indicates rate of correct responding; slope of dotted 

 line indicates rate of incorrect responding. Cumulative response totals are plotted along 

 ordinate, minutes along abscissa. When dotted curve flattens, errors have been eliminated and 

 only correct responding continues. Left curve in each pair indicates a day when left lever is 

 correct; right curve indicates a day when right lever is correct. Large numbers above each 

 pair indicate electric current setting in microamperes of the interference stimulus. In this scries 

 with cortical stimulation, the stimulus does not interfere materially with animal's ability to 

 learn. 



train caused few seizures and caused greater stimulus effects in other 

 respects. 



Some animals were also given a series of special tests which will be 

 described in more detail later. These were (i) a selt-stimulation test tor 

 positive reinforcing effects; (2) a memory-performance test for confusion 

 after criterion is reached each day; (3) a reinforcement-confusion test to 

 find whether confusion persists when electric stimulation is programmed 



