Fiber optic mapping of the Xenopus visual system: shift in the retinotectal projection during development.

Two new techniques for assaying the retina to tectum connections in the lower vertebrate visual system are presented. These techniques allow defined regions of the retina to be stimulated, thus circumventing some of the difficulties of the more conventional retinotectal mapping techniques. Applying these techniques to the Xenopus visual system demonstrates that the retina-to-tectum projection shifts during development. The central part of the retinotectal projection moves medially and caudally about 150 microns (10% of the size of the tectum) in two weeks. The presence of such plasticity in a normal developing animal indicates that the plasticity previously observed in experimentally altered animals probably reflects a normal developmental process.