Studies on the functional significance of efferent innervation in the auditory system: Afferent neuronal activity as influenced by contralaterally applied sound

Summary Recordings were made using stereotaxic techniques from single neurons of the cochlear nucleus of cats in very light barbiturate anesthesia (supplemented by local anesthesia). The responses of afferent neurons to ipsilateral acoustic stimulation were recorded and compared with the responses following binaural stimulation. The sound pressure levels in both ears were kept low enough to avoid interaural cross-talk. It was shown that contralateral stimulation reduced the response of an afferent neuron to ipsilateral stimulation. This inhibition was dependent, on the frequency of the sound presented to the contralateral ear. Adjacent frequencies inhibited more strongly than the characteristic frequency itself or more widely removed frequencies. The dependency of the inhibition on frequency took the form of a W-shaped curve. From this frequency dependent behavior it is concluded that this inhibition leads to an increase of pitch discrimination. This effect can only be explained as resulting from the efferent innervation.Preliminary report of this work was presented at the 34 th Meeting of the Deutsche Physiologische Gesellschaft (March 27–29, 1968, Mainz, Germany).