390 BRAIN MECHANISMS AND LEARNING 



work I Will not need to elaborate it here. Dr Doty in an earlier meeting was 

 interested in the effect of mirror foci in the cerebral cortex, from the point of view 

 of cerebral cortex in the establishment of intracortical conditioned reflexes. I 

 wonder if he has now additional information ? 



Doty. The conditions of our experiments would not have permitted the obser- 

 vation of such a focus. 



Chow. I would like to add a word of caution about the histological pictures Dr 

 MorrcU shov/ed. The R.N. A. staining is a very tricky thing to study unless 

 another stain is used to corroborate this result. Another point is that in the last few 

 years Dr Ricsen, Dr Rush and I studied the problem from another angle, that is we 

 want to study the problem of disuse. We have reared cats, rats, monkeys and 

 chimpanzees in darkness and studied the visual, behavioural and retinal structural 

 effects. We have examined the retina of dark-reared animals with the conventional 

 stain and the R.N. A. stain. In rats, cats and monkeys reared in darkness the retina 

 appeared normal to the haematoxylin and eosin stain, but with the Azure B stain 

 there was a reduction in the content of the R.N. A. of the rod and cones, bipolar 

 and ganglion cells. In the chimpanzee we have observed in two cases, almost 

 complete degeneration of the ganglion cell layer. In these eyes we did not stain the 

 R.N. A. This is the first example we have had of possible structure changes in the 

 visual system in higher animals due to disuse. 



MoRRELL. We have not proved that the histological changes observed are due to 

 neuronal bombardment of these specific cells. Some of the negative observations 

 are consistent with those of Dr Chow in that the area opposite the primary histo- 

 logical lesion is paler and shows a loss of R.N. A. I do not think that the electrical 

 changes can be attributed to denervation sensitization since experiments on the 

 partially isolated cortex in which the coi;pus callosum was intact do not show the 

 characteristic electrical changes. The electrical as opposed to the histological 

 changes in the mirror focus are, I think, a result ot synaptic bombardment. 



Myers. I should like to suggest that the firing of some areas of cortex may be 

 more effective than of others for the elicitation of contralateral effects of the 

 nature under study b)' Dr Morrell. Since he and others have demonstrated the 

 importance of the corpus callosum for the development of the mirror focus it 

 would seem desirable that the areas chosen for the making of epileptogenic lesions 

 have the most dense interhemisphenc interconnections. Such a suggestion may be 

 of more than academic importance inasmuch as there exists profound differences 

 in density of corpus callosum projection from different areas over the cortical 

 surface. The visual receptive area and the primary projection areas in general, 

 including incidentally the somatomotor areas, have the least dense while the 

 adjoining or so-called associative cortex tends to have the most dense projection 

 through the corpus callosum. 



The Pacella Kopeloff^ and Jasper group have carried out a number ot early 

 studies of the mirror focus and, as I recall, investigated the mirror locus using 

 biochemical as well as electrographic techniques. I believe they found significant 

 changes in the chemistry of the mirror focus as compared to normal tissue. I 

 wonder if Dr Morrell recalls what these tmdings might have been in relation to the 

 present discussion. 



Morrell. Although most ot our lesions were placed in visual cortex a good 

 number of them were in somatosensory and in motor cortex. 



