This project has as its major aim the delineation of the manner in which axons conveying information regarding vision and somesthesis are deployed during the development of the superior colliculus. Electrophysiological (single cell recording) experiments have shown that when the afferents from the eye are removed at birth, cells responsive to tactile stimulation can be recorded from parts of the colliculus (the superficial layers) where only visual neurons are normally found. Anatomical studies have demonstrated further that neonatal enucleation results in a dorsal expansion of the collicular territory innervated by axons from the spinal cord, somatosensory cortex and dorsal column nuclei. Experiments are presently being undertaken to determine whether this reorganization is the result of sprouting on the part of these somatosensory projections to the colliculus or a failure to retract by projections which normally innervate the superficial tectal laminae for a limited period during development.