Olivocohlear bundle stimulation: effect on spontaneous and tone-evoked activities of single units in cat cochlear nucleus.

Abstract

The effects of stimulating the OCB [olivocochlear bundle] at its point of decussation in the floor of the IVth ventricle on both spontaneous and tone-evoked activities was studied in 121 single units in cochlear nucleus of unanesthetized, decerebrate cats. Spontaneous discharge rates were unaffected in 51% of the units, decreased in 31%, and increased in 18%. The effects on spontaneous activity persisted beyond the period of OCB stimulation and were often followed by rebound aftereffects. OCB stimulation did not affect tone-evoked responses in 18% of the units, decreased response rate in 37% of the units, and increased response rate in 23%. In the remaining 22% of the units OCB stimulation had complex effects on tone-evoked responses, causing a decrease in activity evoked by tones near threshold intensity and an increase in activity to tones of higher intensity. The occurrence of these different effects could be correlated with the units'' intensity function (monotonic or nonmonotonic), presence of an inhibitory surround, and the changes in spontaneous activity induced by OCB stimulation. There was little correlation of OCB effects with the location of the unit in cochlear nucleus complex or with the unit''s best frequency. OCB stimulation was still effective in modifying spontaneous activity in cochlear nucleus units after destruction of the cochlea ipsilateral to the recording site. This finding suggests that OCB has a direct effect on cochlear nucleus.