The Organization of the Input to Olivocochlear Neurons

University Of Louisville Research Foundation Inc, Louisville KY

Investigators

Abstract

The central auditory system consists of a chain of cell groups, nuclei, that carry and process auditory neural signals from the cochlea, the peripheral sensory organ where sound wave is first converted to neural signals, to the cortex, the highest center, forming the ascending neural pathways. There are also descending pathways in the auditory system along the ascending pathways. The terminal part of the descending pathway is the olivocochlear system, so called because it arises from part of the lower brainstem auditory center, the superior olivary complex, and sends direct feedback neuronal projections to hair cells of the cochlea. Although not well understood, the general consensus regarding its function, based on physiological and behavioral studies, is the enhancement of signal detection in noisy environment and the protection of the auditory system from noise-induced damage, both of which have significant survival value in mammals. While location of the origin of the olivocochlear system is clear, inputs to this system and their organization are still not well known. Physiological and some anatomical studies have allowed speculation that neurons in this system may monitor ascending auditory signals while being controlled by descending inputs from higher centers. This project is designed to clarify the organization of inputs, both from the distant and local sources, to olivocochlear system at the single cell level, using anatomical methods in which a combination of single cell labeling and neural tract-tracing techniques is employed. It is aimed to demonstrate clearly precise input connections, including possible convergence of ascending and descending pathways on the olivocochlear system. The outcome of this work will be significant to understanding the functional role of this feedback system, especially what auditory inputs this system receives, thus processes and passes on to the periphery. Furthermore, the technique established in this project can be used to study other parts of the complex auditory center.