Development of Mammalian Primary Sound Localization Circuits

In order to localize sounds in space, mammals make use of small differences in the timing and intensity of sound between the two ears. These binaural cues are first processed by neural circuits in the auditory brainstem. The intrinsic neuronal properties, precise tonotopic organization, and specialized synaptic structure and function characteristic of these pathways are necessary for their role in sound localization. While some of these characteristics are present from the outset, others mature over a critical period of early development and depend on neural activity. Here we describe key steps in the development of mammalian primary sound localization circuits, discuss the activity dependence of each step, and highlight open questions that require further investigation.