622 GENERAL DISCUSSION 



Dorothea Starbuck Miller (University of Chicago): The fallout background 

 level was rising progressively to a peak in early 1959 and then dropped off. Within 

 three groups of mice, we got three different reactions that were rather revealing. 

 The Fi group is intermediate in susceptibility and there was an astonishingly 

 close parallel. On the first trial, which is the most delicate indicator, as the fallout 

 level went up, the incidence of fatal seizures also went up. At the highest level 

 we scrubbed the mouse quarters thoroughly, removing all the accumulation of dust, 

 and this certainly reduced the local fallout level. 



O. J. Andy (University of Mississipfn, Jackson, Mississippi): The implication 

 of Dr. Monnier's fine paper and the other studies on behavior was that the limbic 

 system was primarily involved in the low dosage irradiations. My question to Dr. 

 Monnier involves an interpretation of his results with regard to the cortex being 

 primarily involved in little higher dosages, and second higher dosages depressing 

 the animal and making it passive. Simultaneously, the hippocampus showed in- 

 creased activity above what it was at the lower dosage, I believe. I think, there 

 was not a depressed cortex, that with higher dosage you could still get the same 

 type of response from the animal with such hippocampal activity. In other words, 

 you may have varying behavior or changes from hippocampal stimulation, the 

 first type displayed, which may result in activation, and the limbic system will 

 cause these tremors in the animals, as Dr. Brown described in burros. If you go 

 above, it is possible to get a discharge in the system, during which time the 

 animal becomes passive and appears depressed. Do you think that the hippo- 

 campus could be primarily involved in this instance, and that the cortex and the 

 thalamus might not be as importantly depressed as you made us believe? 



Joseph Sharp (University of Utah): I would like to know if you used different 

 stimulating parameters in the mesencephalic reticulum to get your EEG changes. 

 The reason I ask this is that in our laboratory we have shown that in using central 

 stimulation for conditioned learning experiments, frequency is important. When 

 we monitor the course of learning on the EEG, we create all kinds of havoc when 

 we vary frequency of stimulation to the mesencephalic reticulum. 



M. Monnier (Basel, Switzerland): It is always encouraging to have converging 

 research results as in the case with Dr. Haley's and Dr. Gangloff's observations. 

 Dr. Caster asked two questions: The first one concerns the correlation of our 

 electroencephalograph findings with biochemical changes. I cannot contribute 

 personally to this question, but I learned yesterday that increased enzymatic 

 changes were found in the hippocampus. This would correspond beautifully with 

 the hyperactivity of the hippocampus in our experiments. Another impressing 

 correlation was the increased fluorescence shown yesterday in the hypothalamus. 

 This corresponds again with the threshold alterations we found in the posterior- 

 ventral hypothalamus. Concerning the second question about audiogenic seizures, 

 these seizures may be correlated with the increased reactivity of all thalamocortical 

 projection systems and of the reticular arousal observed after weak irradiation in 

 our experiments. If you apply stronger doses, the contrary will occur, because the 

 thalamocortical projections arc interrupted at cortical levels. I would expect that 

 higher doses suppress the audiogenic seizures. Dr. Andy raised the question that 

 passivity observed in our animals could not be related to hippocampal discharges 

 into the medial thalamus. Such a mechanism is certainly worth considering. Strong 



