Somatotopic organization of SI corticotectal projections in rats.

The somatotopic organization of somatosensory (SI) cortical projections to the deep layers of the superior colliculus (SC) in rats was examined using neurophysiological micromapping methods. Electrical stimulation of SI produced SC unit responses at the same depths as did peripheral tactile stimulation, in SC laminae IV and VI; mapping of corticotectal projections was performed only in lamina IV. Antidromic activation of the pathway revealed that corticotectal cell bodies are located in SI layer V. Corticotectal projections were found to interconnect only those SI and collicular areas which have similar tactile receptive fields.