A tectocortical visual pathway in the rat

Abstract

Injections of tritiated leucine into the superior colliculus of the rat were used to study the efferents of the colliculus. The superficial layers of the colliculus project to the lateral posterior nucleus, the lateral geniculate nucleus and the pretectum. Two distinct subdivisions of the lateral posterior nucleus were found, a caudomedial region which receives a bilateral projection from the superior colliculus and an anterolateral region which receives a unilateral projection from the superior colliculus. Injections of horseradish peroxidase into the lateral prestriate visual cortex showed that the lateral posterior nucleus sends a dense projection to this area. There was no evidence that the caudomedial and anterolateral parts of the lateral posterior nucleus project to different regions of the lateral prestriate cortex. The tectothalamocortical pathway in the rat provides a major route outside the geniculostriate projection by which visual information from the retina can reach the cortex.