Organization of retinocollicular pathways in the cat

A direct pathway from the temporal retina to the contralateral superior colliculus has been demonstrated using anterograde degeneration methods. This observation of a crossed pathway to the most rostral pole of the colliculus confirms electrophysiological evidence that within each colliculus the whole eye, rather than just its hemiretina is represented. Autoradiographic tracing methods have been used to study the total tectal projection of each retina. Following intreocular injections of 3H proline, there is dense label in most of the superficial gray of the contralateral colliculus, but in this region there are several small areas of only relatively sparse label. In contrast, the superficial gray of the ipsilateral colliculus contains islands or patches of transported label. These patches are present throughout an extensive region of the colliculus and suggest that the ipsilateral retinocollicular pathway in the cat may be more substantial than earlier reports have indicated. There is no ipsilateral label within the most caudal parts of the colliculus which receives afferents from the monocular crescent of the rostral pole is free of ipsilateral input, and we suggest that this corresponds to the region receiving the crossed input from the temporal retina.