FRANK MORRELL 391 



Myers. Again, it seems that these three cortical areas have least to offer in terms 

 ot contralateral firing. 



MoRRELL. One of the reasons why most ot our lesions have been made in sensory 

 areas is that epileptogenic lesions of the motor cortex often produce clinical seizures. 

 These mav result in death of the animal or may require anticonvulsant treatment, 

 and this of course complicates the experiment. 



Myers. Have you had the opportunity to study species variation in regard to the 

 development of contralateral toci of independent tiring? 



MoRRELL. I have not had time to delineate species variation in the development of 

 secondary foci. However, we have done these experiments in rabbits, cats and 

 monkeys and have been able to demonstrate ditferences in the time required for 

 the establishment of mirror toci in each of these animals. In the cat and monkey it 

 is much longer than m the rabbit. Penfield has made the statement that if a lesion 

 has been present for approximately 2 years (monkey) ablation ot the primary site 

 docs not lead to disappearance of the mirror focus. 



Myers. Was Penfield's data related to cortical areas other than the temporal tip. 



MoRRELL. In motor cortex. 



Naquet. You said that the isolated cortex in the normal animal has a higher 

 threshold than in your preparation. 



MoRRELL. In preparations with well-developed secondary toci there is, oi course, 

 no normal side. The threshold to electrical stimulation oi the non-epileptic isolated 

 cortex is higher than that in the adjacent surrounding cortex. 



Naquet. I agree but I feel that we cannot compare what happens in the isolated 

 cortex when you stimulate electrically to what happens spontaneousK'. I think we 

 mav ask Dr Garcia-Austt what he thinks about it. 



MoRRELL. There have, as you arc all aware, been great disputes as to whether 

 spontaneous rh\thms are present in completely neuronally isolated cortical 

 tissue. It is obviously impossible, even with serial sections, to be sure that no 

 threads of tissue remain connecting the cortical slab to the surrounding brain. 

 Nevertheless, in our experience, if good isolation is achieved there is no clearly 

 demonstrable spontaneous parox\'smal epileptiform activity in the isolated region. 



Fessard. Sensitization of isolated slabs of cortex to acetyl-choline is a fact that 

 has been carefully studied recently in monkeys by Dr Frank Echlin. His paper will 

 come out soon in the EEG Journal. Have you heard of this work? It impressed me 

 much when I visited Dr Echlin recently in New York. 



Morrell. We have not placed acetyl-choline directlv on isolated cortical regions. 

 With electrical stimulation the non-epileptic isolated slab has a higher threshold 

 than normal cortex. 



LissAK. Regarding Dr Fessard's question, some 10 years ago with my colleagues 

 Dr Endroczi and Dr Hasznos we did some experiments on isolated cortex. We 

 found an increased sensitivity to acet}l-choline and we determined the choline 

 esterase activity too and wc found that it was decreased not only in the isolated 

 cortex but also to some degree in the contralateral mirror part of the cortex. 



Garcia-Austt. I would like to ask some questions. Wc also have been working 

 with isolated cortical slabs. We think that the slabs have a greater capacity to 

 respond with a seizure to stimulation and also to spontaneous seizure discharge. 

 As to the threshold — we have not studied it as measured by the threshold voltage 

 to give a seizure — but we found that post-discharge, if measured half an hour 



