Intertectal crossing of optic axons after tectal fusion in neonatal rats.

Surgically-induced fusion of the superior colliculi along the midline was performed in newborn rats to provide a bridge for optic axons from one eye to cross the tectal midline. The results indicate that although tectal fusion is a necessary condition of optic axons to cross from one side of the midbrain to the other, it is not sufficient by itself to induce crossing unless the optic input from the opposite side is also removed. This finding is discussed in relation to tectal lesion studies and is compared with our previous observations of the corticotectal pathway.