Somatotopic and columnar organization in the corticotectal projection of the rat somatic sensory cortex.

Single injections of tritiated amino acids into the first somatic sensory area (SI) of the rat neocortex result in axoplasmically transported labeling of the stratum griseum intermidiale and stratum griseum profundum of the ipsilateral superior colliculus. The terminal labeling in these layers takes the form of multiple, column-like patches. The SI projection is somatotopically organized with the face and head representations projecting to an extensive anterolateral part of the colliculus and the limb representations projecting to a restricted posterolateral part. Injections of horseradish peroxidase into the superior colliculus result in retrograde labelling of corticotectal cells in the superficial part of layer VB of SI and of the second somatic sensory area (SII).