Topographical representation of the visual field on the cerebral cortex of the rat

Abstract

The purpose of this study was to establish electro- physiologically the projection of the visual field on the cerebral cortex of the rat, to relate this to what is known about vision in the rat, and to compare it with the cortical projection established for other mammals.The projection of the visual field on the cerebral cortex of the rat has been studi:ted using electro- physiological methods, and the techniques used for anaesthesia, preparation, stimulation and recording have been described.The borders of the visual area of the cerebral cortex have been defined except laterally, and its position on the cortex has been compared with that described by other writers.The visual area has been sub -divided into a primary visual area - visual I, visual II and provisionally, visual III, on a topographical basis, as has been done for the cat. Visual I and visual II each contain a topographically well organised projection of the whole visual field, that of visual II being a smaller mirror image of that in visual I. A map has been drawn of the visual field projection to visual I, but not of the projection to visual II. The anterior part of visual III seems to be devoted to a relatively small part of the visual field, a part found also to have a large representation in visual I, and a relation is postulated :between this area and an efferent projection to the superior colliculus.The map of the projection of the visual field on visual I shows magnification of two areas, and this has been correlated with previous retinal ganglion cell counts.An attempt has been made to. compare the visual system of the rat with that of primates and cats whose visual space is divided vertically at the mid-line, each half of the visual field projecting to the contralateral cerebral hemisphere, but there is not sufficient experimental evidence to establish the degree of similarity or difference between them in this respect.It is likely that the rat has a considerable amount of binocular vision, and that it possesses eye movements of both convergence and axial rotation.