Auditory Mechanisms of the Lower Brainstem

Abstract

Brainstem centers of the mammalian auditory system have been under intensive investigation over the past few years. Anatomical, electrophysiological, and bio­ chemical techniques have all been brought to bear on the complex mechanisms by which these centers process acoustic information. In this article, we review work on two closely related cell groups in the auditory pathway, the cochlear nuclei and the superior olivary complex of the medulla and pons, which form major links in the synaptic chain between auditory nerve fibers, on the one hand, and higher auditory centers on the other. The cochlear nuclear complex is the first synaptic station in the auditory pathway. It is within this region that all information encoded in primary auditory nerve fibers is received and recoded. Neurons of the superior olivary complex are principal targets for cells located throughout the cochlear nuclei and are among the first cells to receive and process binaural input. Reciprocal connections between these two structures establishes a basis for functional feedback loops, while a pathway from the superior olivary complex to the cochlear hair cells provides a route for possible central control of primary afferent input. Thus, under­ standing the mechanisms by which information is processed within these brainstem areas is critical to understanding the function of the entire auditory system. We have selected material that we believe represents the current state of understanding in this rapidly moving field of mammalian sensory physiology. There are other reviews of some of this work and related studies (Hawkins 1964, Eldredge & Miller 1971, Erulkar 1972, MS'lller 1972, Harrison & Howe 1974a,b, Evans 1975, Goldberg 1975, Webster & Aitkin 1975).