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
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