Physiological and anatomical mechanisms of temporal sharpening in the auditory brainstem

Hearing depends on eardrum vibrations, which typically follow a complicated pattern that is the sum of many vibration patterns of different sound sources and their echos. A fascinating but illunderstood feature of hearing is that it can disentangle and interpret this summed pattern so that we perceive the original sound sources rather than a blur. For example, we hear the different instruments in the sound of an orchestra despite the strong overlap of their sounds in frequency and in time: our brain is able to parse frequency components and to “reconstruct” the original sound sources. The same process allows us to understand a single speaker amongst many other speakers in a crowded environment. This process of “scene analysis” starts with frequency filtering in the inner ear, but also heavily relies on time processing in the nervous system. For example, different frequencies originating from a single sound source tend to start and end at the same time, and tend to be synchronously modulated in amplitude or frequency, while frequencies generated by another source start and end and are modulated at other times. We study a type of neuron in the brainstem that integrates neural signals from different points in the inner ear. We examine how this integration generates new neural properties and sensitivities which support scene analysis. We also develop and use a tracing technique to examine how this integration depends on anatomical connections