J. OLDS AND M. E. OLDS I65 



(3) Correlation with Sclf-Stiiinihnioii. — In an effort to test for such a 

 correlation, forty-six animals with electrodes placed diversely throughout 

 the brain were tested first for interference and later for the self-stimulation 

 effect. The result was a most remarkable correlation. Of eighteen animals 

 completely confused by the electric stimulus, fifteen were self-stimulators. 

 Of seventeen animals unaffected, fourteen were non-self-stimulators 

 (Fig. 11). Of eleven animals moderately impaired by the stimulus, seven 

 were self-stimulators. All told, there were only three cases of definite 

 impairment that were non-sclf-stimulators; and there were four cases of 

 ambiguous impairment. 



A first answer is, therefore, that points yielding the most interference in 

 a learning experiment are the points which also cause self-stimulation. A 

 question arises, however, whether the points which cause interference 

 but no positive reinforcement occurred by chance, or whether they 

 follow some pattern. Mapping the points (Fig. 12), we see that there is a 

 design. Of the twenty-nine points yielding complete or ambiguous 

 impairment, we have satisfactory histological localization on twenty-six. 

 The points which yield both confusion and self-stimulation arc scattered 

 throughout the hypothalamic-palaeocortical system, but the points which 

 yield only confusion are clustered along the hippocampus proper (that is, 

 as distinct from the dentate gyrus), plus one in the anterior thalamus. 

 We may guess, then, that there are two kinds of confusion points: (1) the 

 self-stimulation points, and (2) a second kind located mainly in the 

 hippocampus proper. 



(4) Memory Test. — A further difference between these two kinds of 

 points appears when we test for confusing effects of the stimulus on on- 

 going performance, after criterion has been reached on a given day. We 

 have called this, perhaps wrongly, a memory test because we introduce 

 the jamming stimulus after learning has occurred, and we look to see if 

 the animal can still 'remember' the correct way. We might equally well 

 call it a performance test, inasmuch as the stimulus might interfere with 

 correct performance even if some hypothetical 'memory' were intact. 



At any rate, the test shows up a striking difference between two kinds 

 of placement. If electrodes are in placements which produce avid self- 

 stimulation, the stimulus causes a complete relapse to errors (and errors 

 continue indefinitely) when stimulation is introduced after learning. But 

 if electrodes are in the interference points where this is dissociated with 

 self-stimulation, the result is different. The animal may make a few errors 

 upon initial introciuction of the stimulus, but correct performance is 

 readily resumed (Fig. 13). 



