Plasticity of tonotopic maps in auditory midbrain following partial cochlear damage in the developing chinchilla

There is substantial reorganization of the midbrain (inferior colliculus) t onotopic map following neonatally induced partial cochlear lesions in the c hinchilla. The most obvious feature of this remapping is a large "iso-frequ ency" region in the ventral sector of the central nucleus of inferior colli culus (ICC). Neurons in this region exhibit similar threshold and tuning pr operties, with a common characteristic frequency which corresponds to the h igh-frequency audiometric cutoff. This overrepresented frequency range also corresponds to the high-frequency border of the cochlear lesion. Alteratio ns to the tonotopic map corresponding to lower frequencies, in more dorsal regions of ICC, depend on the extent and degree of the cochlear lesion. Whe n there is minimal damage to apical (low-frequency) cochlear areas, the dor sal ICC has relatively normal frequency representations. With more extensiv e apical cochlear lesions there is a corresponding disruption of ICC tonoto pic representation of the low frequencies. We conclude that the tonotopic m ap within the TCC can become (re)organized postnatally according to the abn ormal pattern of neural activity from the auditory periphery. Similar reorg anization can be expected to occur in human infants with a partial cochlear hearing loss from birth.