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The history of the discovery of the visual cortex is reviewed and previous investigations on the corticofugal fibre connections from the visual cortex to the brain stem area presented. Efferent fibres from the visual striate cortex to the lateral geniculate body of the monkey have been investigated, following striate cortex ablation. Sections at five different points through the lateral geniculate body were stained with Del-Rio-Hortega’s double impregnation method and have been examined for fibre and "bouton terminaux" degeneration. Two other stains, Nauta and Gygax silver stain to further determine degenerating fibres, and Einarson's chrom alum stain to differentiate the structures within the sections, were used for this investigation. Experimental results showed that there was a consistent increase (with an exception of one section) in the number of boutons on the side corresponding to the lesion. This increase is statistically significant. The presence of a substantial volume of degenerating fibres and an abundance of heavily stained, almost solid type of "bouton terminaux" occurring on the side of the lesion has strongly suggested that there are actually a number of corticofugal or efferent fibres from the striate area to the lateral geniculate body. / Medicine, Faculty of / Graduate

In the present investigation the effect on brightness discrimination of ablations of various parts of the cerebral cortex of cats has been examined. The background for this project lay in the work of Kluver and Bucy (1939) who observed "psychic blindness” in monkeys with bilateral temporal ablations and that of Chow, Blum and Blum (1951) and Riopelle, Alper, Strong and Ades (1953) who found no such loss of simple visual properties from similar ablations in monkeys. Since it is not possible to subject the cat to the complex experimental tests of the monkey, and since a rigorous control of the stimulus situation was desired, the present investigation deals with brightness discrimination only. It was found that bilateral ablations of the cerebral cortex had a deleterious effect on brightness discrimination. The specific test did not differentiate among the effects of ablations of the frontal, temporal and parietal association areas although the total post-operative behavior of the animals easily indicated the specific site of the lesions. / Medicine, Faculty of / Graduate

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