Correlated studies of the ear and brainstem in deaf and hearing white cats have demonstrated early and progressive changes both peripherally and centrally, including organ of Corti degeneration, loss of spiral ganglion cells and auditory nerve fibers and decrease of neuronal size in the medial superior olivary nucleus (MSO). Loss of synaptic appositions on MSO neuronal perikarya is already pronounced in the youngest deaf animal, a time before the spiral ganglion cell population has decreased significantly. Thus, spiral ganglion cell populations alone cannot be used as a reliable indicator of the integrity of the central auditory pathways.