J. OLDS AND M. E. OLDS 185 



larly in planned behaviour, I had very much a similar notion after this work 

 because we interfered completely with stimulation in hippocampus and I felt that 

 the hand-in-glove arrangement between hippocampus and dentate cannot be for 

 nothing, hi the single unit studies we tound the most remarkable mechanism-like 

 effects in the outflow from the dentate itself where we could give two or three 

 stimulations in a reinforcing position, that is following the response, and then 

 multiple firing would suddenly ensue. 



Magoun. Stimulating ascending pathways to the rabbit's hippocampus evokes 

 an undulating slow-wave discharge whose frequency is around 5 to 7 a second. 

 Unit recordings from the hippocampus, by Dr John Green, often show firing in 

 some relationship to this ryhthm. Did you elicit such a rhythm from stimulating 

 reinforcing sites? if so, could you correlate unit tiring with the slow waves? 



Olds. We do not have fair data to answer that. Because wherever we got an 

 elicited effect we went on very rapidly to another unit. Quite often units would 

 respond on slow waves, this being rather hard to see when you have a lot of filters, 

 but still it was rather obviously there and it made the unit an unlikely one for 

 further recording. We did not spend much time with units that were associated 

 clearly with slow waves. Thus in a sense we have worked out of our population 

 a lot of material which you would like to have and we will certainly go back and 

 look at it later. 



Segundo. It seems opportune to mention observations performed upon human 

 subjects that illustrate contrasting features of archi- and palaeo-cortices. Firstly, 

 excitation effects of hippocampus or fornix that included somnolence or even slight 

 blurring of consciousness, a result has that not been encountered in extensive explora- 

 tion of the human neocortical mantle (Pentield, and Rasmussen, 1950; Segundo, 

 Arana, Migliaro, Villar, Garcia-Guelfi, and Garcia-Austt, 1955). Secondly, the 

 report by Griinthal of dementia produced by hippocampal atrophy (Griinthal, 

 1947); neocortical lesions of comparable size do not provoke dementia. This 

 material stresses the manner in which interference with hippocampal mechanisms 

 affects behaviour, thus supporting Dr Olds's observations. 



KoNORSKi. Did you try to use as reinforcing agent self-punishing points instead 

 of self-rewarding ones? It is interesting to see whether in this case the units, whose 

 activity you observe, will behave in the same way as in your experiments or, on 

 the contrary whether they will stop firing, when their activity is negatively 

 reinforced. 



Olds. The positively reinforcing points interfered with learning. Then we have 

 anecdotes on the negative reinforcing points which show they do not interfere with 

 learning in any similar fashion. But we do not have full evidence, just anecdotes, 

 which make us sure that we will find that the negative reinforcing points do not 

 interfere with learning. 



As for slowins; the units, I believe asain on the basis of anecdotes, the answer 

 will be yes. In the early days of tliis experiment we had animals that were tested 

 for self-stimulation but we did not find whether they were also escaping and I have 

 had an animal that I worked on for a period of almost 24 hours and every unit that 

 I ever tried to reinforce was slowed. Since then I think that when we do study the 

 negative reinforcement we should find that it will work. 



BusER. I wish to mention here some observations made on rabbits, by Dr 

 Cazard and myself, on the effect of repetitive stimulation of the dorsal 



