Bilateral cortico-tectal projection from the visual cortex in the cat

Abstract

THERE is anatomical and electrophysiological evidence for a heavy and well organised fibre projection from the visual cortex on the superior colliculus of the midbrain in several species^1–4. In the cat, areas 17, 18 and 19 of the visual cortex each project to the colliculus and the arrangement is such that a point in the cortex related to a particular part of the retina sends fibres to that part of the colliculus receiving fibres directly from the same part of the retina. The available evidence is for a cortico-tectal projection to the ipsi-lateral superior colliculus only. In several brains of cats with lesions involving the visual cortex of one hemisphere, fibre degeneration has now also been found in the superior colliculus of the opposite side. This observation provides an explanation for several findings made in electrophysiological studies of the representation of the visual field in the superior colliculus which have been difficult to interpret, and it should help in the interpretation of functional studies on the visual connections of the cerebral hemisphere.