The corticopontine projection from the visual cortex of the cat: An autoradiographic investigation

Abstract

AbstractThe cortico‐pontine projections from striate (kV), parastriate (paV) and peristriate (peV) areas of the neocortex of the cat have been investigated using an anterograde axoplasmic tracing method. Injections of tritiated amino‐acids have been made at cortical locations whose visual field positions were determined in some experiments electrophysiologically. It has been found that the density of the projection varies depending on the location of the injections within each area. In addition differences in the density of the pontine projection have been found between the three visual areas. Both in kV and paV no pontine projection was detected from cortex representing the area centralis. An increase of the projection from cortex with paracentral to peripheral visual field representations was found in kV for the lower hemifield (the upper hemifield has not been investigated) and in paV for the entire hemifield. In addition it has been found that a denser projection arises from the representation of the lower visual field in paV and peV than from the representation of the lower visual field in paV and peV than from the representation of the upper visual field.The cortico‐pontine projection has been found to increase from kV (V1) through paV (V2) to peV. Since the injections in peV were not restricted to the region of the third visual representation (V3), they do not allow a definite conclusion to what extent the increased projection from peV can be attributed to V3.The terminations from the three visual areas are largely restricted to the rostral third of the pontine basilar gray. The labelled terminals were not restricted to any one of the nuclei of this region which have been delimited by Brodal and Jansen ('46). The terminals formed patches of variable size near the ventral aspect of the cerebral peduncles. A clear retinotopic distribution of these patches could not be demonstrated.