J. OLDS AND M. E. OLDS 1 83 



tendency to repetitive behaviour. The pattern of repetitive firing in the 

 units of this same system is the residual process which is modulated by 

 instrumental-conditioning techniques. 



As to whether the same changing pattern of residual processes might 

 serve as a model for associative conditioning, we will suspend judgment. 



GROUP DISCUSSION 



Gerard. In what manner are your experiments different in principle — ob- 

 viously they are more elegant in degree — than ones using any other kind of 

 effector response? Any response obviously must involve the discharge of some unit 

 somewhere in the brain. 



Olds. Two answers. In the case of the cortical unit and even in the case of the 

 anterior rhincncephalic unit that I showed, my impression is that there is no 

 difference m principle at all. My feeling is, in both these cases, that the animal 

 decided that doing something was getting him reinforced and so he did it. In the 

 case, however, of the fimbria and dentate gyrus units and in the case of some of the 

 liippocampals, I had a feeling that here is the mechanism, so to speak, so that you 

 would say 'this is the stuff decisions are made out oC. That here we were playing 

 with sornething that just automatically had its response rate augmented if we 

 stimulated the hypothalamus right after it has discharged. 



Gerard. Did you say that stimulation of the fornix in the rat, under your condi- 

 tions, interferes with learning f 



Olds. No. The answer is that in the hippocampus proper wc interfered. But in 

 the fimbria and often in the fornix our stimulation usualK* produced seizures before 

 we could get any experimental tests. 



Gerard" I raised the point only because of the recent report of an unfortunate 

 operation on man, in which the fornix was cut bilaterally. Recent memory was 

 completely abolished. 



Olds. I have a hunch that response Icarnnig and recent memory are somehow 

 very closely related. And that if we said response learning and recent memory 

 involve palaeocortical and hypothalamic systems we might be on to something, and 

 the more structured memory might be, it seems to me, in the neocortex and the 

 classical thalamic system. 



Grastyan. Bv stimulation of the hippocampus we got similar observations in 

 somewhat different experiments. On the background of already established condi- 

 tioned reflexes we obtained always an inhibition. The interpretation of these 

 observations was, however, always very problematic. It is well knowii that the 

 hippocampus is one of the structures that has the lowest threshold for eliciting after- 

 discharges. I see that you disregard the experiments in which you elicited after- 

 discharges. I am still not absolutely convmced, however, that by stimulating the 

 liippocampus you did not get any after-discharge in the hippocampus itself 

 Sometimes when recording in various parts of the hippocampus we got after 

 discharges when we did not see any sign of after-discharge in other structures. I am 

 not convmced that these effects represented a physiological inhibition. I have to 

 admit at the same time that we had some observations m wliich we did not elicit 

 any after-discharge in the hippocampus and we still obtained inlnbition. I would be 



