The neocortical projection to the inferior colliculus in the albino rat.

The purpose of the present study was to define the field of termination of the neocortical projection to the inferior colliculus in rat. The study was based on fiber degeneration following large lesions of the cerebral cortex, and anterograde transport of wheat germ agglutinin horseradish peroxidase ejected iontophoretically into more restricted neocortical loci. Neocortical fibers were found to supply the dorsal and external cortices of the inferior colliculus. The central nucleus, in contrast, did not receive such fibers. The results speak in favor of three separate projections, one partly bilateral to the deeper part of the dorsal collicular cortex, a second ipsilateral to the superficial part of this subdivision, and a third ipsilateral to the external collicular cortex.