1 86 BRAIN MECHANISMS AND LEARNING 



hippocampus on ncocortical evoked potentials. It appeared that a short tetanization 

 of the hippocampus (subhminal for producing any hypersynchronic or paroxystic 

 phenomenon), was toUowed by a net increase (lasting up to 30 minutes) of the 

 amplitude of cortical sensory responses (primary as well as motor irradiated 

 evoked potentials). These effects were obtained on acute (chloralose or curarized 

 unanacsthcthized) as well as chronic preparations. 



Olds. I believe that that sounds extremely pertinent. Ot course under anaesthesia 

 the evoked potentials are also augmented, is that truef 



BuSER. Yes, under anaesthesia and also in caudate rabbits. 



Olds. So it does look as if the same function could be involved in both of our 

 situations. 



RosvOLD. I was wondering whetlier there is any difference in your results 

 between the caudate and the hippocampus or whether you think they are very 

 similar. 



Olds. There is a difference. Of course, because of the internal capsule it is very 

 difficult to know when you are stimulating caudate and not internal capsule too. 

 We found that all our caudate stimulators produced associated movements of one 

 sort or another. Very often in the case of the ambiguous caudate results we were 

 quite sure that the animal was trying to do one thing and being forced to do 

 another by the stimulus. We found that also inevitably with caudate stimulation 

 the running ceased, that is, the animal simply would not run at all. It looked more 

 like total disruption. I might even be tempted to say that even long-term memory 

 was disrupted in these cases. 



RosvoLD. Do you suppose that the stimulation of the hippocampus jams the 

 function of the hippocampus or excited it? 



Olds. I think it is interfering. I find- it hard to think of a stimulation in a 

 learning experiment of doing something to organize a pattern, though stimulation 

 of certain places of the reticular formation has been shown to augment certain 

 kinds of perceptual tasks, but I regard this as an exception. 



Myers. What proportion of your attempts to condition rhinencephalic neurones 

 has resulted in failure; 



Olds. We have never had a failure of the sort we have had with cortical units 

 with rhinencephalic units. We have had a failure of the experiment either because 

 we reinforced too soon ; its activity remained high and we could not use it further, 

 because we could not find whether we had elicited it or not. Similarly we have had 

 cases where we thought we had something to work with but after trying to 

 reinforce silence, the response did not come back. But this cannot be said to be a 

 failure to reinforce. With cortical units, we have had the unit going for periods of 

 5, 10, 15 minutes, reinforcing regularly and failed to augment its firing rate. This 

 has happened many times with ncocortical units but never with palaeocortical 

 units so far. 



Myers. Have you seen evidence that the conditioning of one unit has any 

 influence on the conditioning of other units in the neighbourhood. 



Olds. Yes. This is a definite thing. Quite surprising and I don't know quite how 

 to put sufficient constructions on the situation to explain it. We found some situa- 

 tions where we had one unit in an area, and reinforced it. Eventually it went into 

 continuous firing. Its amplitude decreased and it finally disappeared and it sub- 

 sequently was replaced and we reinforced the other one, and those two then 



