Electrophysiological and anatomical evidence for a direct projection from the nucleus of the basal optic root to the nucleus rotundus in pigeons

A direct projection of the nucleus of the basal optic root (nBOR) onto the nucleus rotundus (Rt) in the pigeon would link the accessory optic system t o the ascending tectofugal pathway and could thus combine self- and object- motion processes. In this study, injections of retrograde tracers into the Rt revealed some cells in central nBOR to project onto the ipsilateral Rt. Contrary, injections into the diencephalic component of the ascending thala mofugal pathway resulted in massive labeling of neurons in dorsal nBOR. Sin gle unit recordings showed that visual nBOR units could be activated by ant idromic stimulation through the Rt. Successful collision tests applied to n BOR cells revealed that the connection between nBOR and Rt is direct. These data provide strong evidence for a direct and differential projection of n BOR subcomponents onto the thalamic relays of the two ascending visual path ways. (C) 2001 Elsevier Science Ireland Ltd. All rights reserved.