In this series of studies sophisticated track tracing experiments at a light and electron microscopic level will be used to examine development/plasticity during the first two months after onset of hearing in the ferret. Proposed studies will focus on altered laterality of afferent projections from and to brainstem auditory nuclei. These studies will examine if exuberant proliferation with subsequent refinement of lateral superior olivary nucleus projections and/or refinement of synaptic circuitry occurs in the IC. This first series of studies will serve as a baseline for studies of monaural deprivation. Deprivation studies will help determine the possible role of competition between pathways excited by each ear in developmental plasticity. Both monaural and binaural deprivation using ear plugging will be used to alter the auditory experience during the first two months after onset of hearing in the ferret. Results should lead to a better understanding of the influence of experience on the development of these binaural sensory pathways.