Effects of chronic cochlear de-efferentation on auditory-nerve response

The olivocochlear bundle was sectioned at the floor of the fourth ventricle in a series of cats. From three to thirty weeks post-operatively, recordings were made from single auditory-nerve fibers. Tuning curves, spontaneous discharge rates, and rate-level functions for tones at the characteristic frequency were measured and compared to normal data. Light- and electron-microscopic analysis of the cochleas suggested the lesions were complete, for both classes of cochlear efferents, in three cases. Electrophysiological data from these cases showed normal thresholds, tuning curves and rate-level functions; however, the distributions of spontaneous activity suggested significant decreases in average rates in the de-efferented cases.