UC Irvine

THE OLIVOCOCHLEAR BUNDLE (OCB) is known to modify afferent auditory input at the cochlea. Electrical stimulation of the bundle in the floor of the IVth ventricle causes a suppression of neural response to clicks recorded at the cochlea (lo), and a paradoxical enhancement of microphonics (8). Fex (8) and, more recently, Wiederhold (23) have shown that both spontaneous and tone-evoked activities of single units in the VIIIth nerve are similarly suppressed during such OCB stim- / J while the carotid arteries were ligated, a trephine ulation. The purpose of the present study was to investigate the effects of OCB stimulation on spontaneous and tone-evoked activities of single units in cochlear nucleus, the first central auditory station receiving cochlear input. Rasmussen’s finding that OCB collaterals terminate in cochlear nucleus (1 S), raises the possibility that this efferent system may have a central regulatory role as well. Our results indicate that OCB stimulation can modify cochlear nucleus units in a variety of ways. Al though suppression of spontaneous activity was frequently observed, there were many units in which OCB stimulation affected an increase in spontaneous discharge rates. Furthermore, the effects of OCB stimulation on tone-evoked responses were found to vary with tone intensity in complex ways.