Progressive alterations in cochlear nucleus, inferior colliculus, and medial geniculate responses during acoustic habituation

Abstract

Multiple unit activity in auditory relay nuclei was studied during repeated tone or white noise presentations in cats immobilized by a neuromuscular blocking agent. Cochlear nucleus, inferior colliculus, and medial geniculate body showed characteristic patterns of integrated multiple unit responses with increasingly prominent amounts of inhibition evident at the more central sites. Progressive changes in response to constant repeated acoustic stimulation occurred at all levels of the auditory system. The cochlear nucleus showed a significant and repeatable attenuation of multiple unit acoustic responses in 71% of the habituation sequences, 10% showed a progressive increase in activity during stimulation, and 19% no significant change. A significant progressive decline in responsiveness was shown in 42% of the total collicular runs, 16% showed an increase in the original response, and 42% no change. Generally, similar findings were shown at the medial geniculate body. The responses were independent of alterations in activity during the prestimulus period and were uninfluenced by the middle ear musculature in the paralyzed preparations. Significant progressive changes of multiple unit responses occurred during auditory habituation at the most peripheral auditory relay, the cochlear nucleus, as well as in the more central inferior colliculus and medial geniculate body.