The Generation of Binocular Maps in the Hamster Superior Colliculus: Normal and Neonatally Enucleated Animals

Abstract

In the mammalian retinotectal projection, the existence of direct binocular projections exhibiting congruent binocular receptive fields requires that the nasotemporal axis of the retina displays mapping rules of opposite polarity for the crossed and uncrossed projections. The aberrant ipsilateral retinotectal projection arising after neonatal removal of one eye has been mapped in the hamster to investigate possible strategies for determining the normal differences in mapping polarity. The ipsilateral retinotectal projection in enucleates displays a dual representation which is mirror-symmetric about the representation of the temporal retinal margin. In rostral tectum, temporal retina maps with a polarity appropriate for an uncrossed projection whereas in caudal tectum both temporal and nasal retina are mapped, with a polarity appropriate for a crossed projection. Although two mapping polarities are present in a single projection, neighbour relations are preserved insofar as adjacent points on the tectum receive input from adjacent points on the retina. Possible implications of this mapping will be discussed.