Our long term goal is to understand the neural codes and computations that underlie hearing. All acoustic information is presented to the brain with the synapses formed by auditory nerve fibers in the cochlear nucleus. Here, the data contained in the nerve are distributed amongst a variety of cell types that each represent some feature of the acoustic environment. Cochlear nucleus neurons and their neural codes form the foundation of central auditory pathways that are ultimately responsible for our ability to locate and identify a sound: perceptions that collectively we refer to as hearing. How and where the neural computations that underlie these perceptions occur will depend on the axonal pathways engendered by distinct classes of cochlear nucleus neurons, and their synaptic organizations in the structures that they target. In this proposal, we plan to study the axonal pathways borne by one large group of cochlear nucleus neurons referred to as multipolar neurons. We propose that multipolar neurons in the ventral division of the cochlear nucleus play a key role in the initial stages of acoustic information processing. They are full participants in the intrinsic circuitry of the cochlear nucleus and their axons target every brain stem nucleus in the auditory pathway. Multipolar neurons are a heterogeneous population, suggesting that they are comprised of several distinct subclasses of cells. We propose to use retrograde pathway tracing methods to identify the targets of different populations of multipolar neurons, and electrophysiological recording techniques to match the axonal pathway of each type with its physiological response properties. These data will provide new knowledge with respect to the functional roles served by a large group of cochlear nucleus cells, as well as provide insights into the nature of the neural computations performed in central auditory nuclei.
