A crossed corticotectal projection from the lateral suprasylvian area in the cat.

Crossed cortical projections to the superior colliculus of the cat were demonstrated by unilateral superior colliculus injections of horseradish peroxidase (HRP) and by cortical injections of radioactive amino acids. This crossed corticotectal projection originates in the lateral bank of the middle suprasylvian sulcus and in both banks of the posterior suprasylvian sulcus. The site of termination of the contralateral corticotectal projection is restricted to the anterior margin of the superior colliculus (SC) while the ipsilateral projection spreads over the whole SC. The contralateral terminal areas are restricted to the superficial tectal layers. The projection fibers reach the contralateral superior colliculus by crossing the collicular commissure. The existence of such a connection may help to explain certain electrophysiological observations.