Neural Mechanisms of Encoding Binaural Localization Cues in the Auditory Brainstem

Abstract

When an animal hears a sound in its environment, there are several important tasks that the auditory system must try to accomplish. Two major jobs are to determine what it was that produced the sound and where it comes from. Understanding how the nervous system can accomplish these tasks is a major goal of modern auditory neurobiological research. In this book, we explore what is known about these questions at several different levels of the auditory system. The purpose of this chapter is to review the anatomical and physiological mechanisms in the auditory brainstem of mammals that encode where a sound originates. Specifically, this chapter examines the two binaural localization cues: interaural time disparities (ITDs) and interaural level disparities (ILDs) (For abbreviations, see Table 1). The neural mechanisms of sound localization are of particular interest since the location of a stimulus is not represented in the sensory epithelium, as it is in the visual or somatosensory systems, but must be computed by combining input from the two ears in the central auditory system. To a large degree, we understand how these cues are encoded by single cells at this level of the auditory system. Indeed, it appears that certain cells in the auditory brainstem are highly specialized to facilitate the encoding of these cues, and more is known about the central processing of sound localization cues than of any other auditory function (e.g., pitch perception, vowel discrimination).