Tonotopic reorganization of developing auditory brainstem circuits

This review summarizes recent work in auditory brainstem nuclei to demonstrate that developing brain stem circuits are subject to experience-dependent synaptic refinement. This is in contrast to the traditional view, which interprets the early development of brain stem tonotopy as indicative of a 'hard-wired' mechanism. A fundamental organizing principle of auditory brain circuits is tonotopy, the orderly representation of the sound frequency to which neurons are most sensitive. Tonotopy arises from the coding of frequency along the cochlea and the topographic organization of auditory pathways. The mechanisms that underlie the establishment of tonotopy are poorly understood. In auditory brainstem pathways, topographic precision is present at very early stages in development, which may suggest that synaptic reorganization contributes little to the construction of precise tonotopic maps. Accumulating evidence from several brainstem nuclei, however, is now changing this view by demonstrating that developing auditory brainstem circuits undergo a marked degree of refinement on both a subcellular and circuit level.