ABSENCE OF PLASTICITY OF THE FREQUENCY MAP IN DORSAL COCHLEAR NUCLEUSOF ADULT CATS AFTER UNILATERAL PARTIAL COCHLEAR LESIONS

In adult animals, lesions to parts of the auditory receptor organ, the cochlea, can produce plasticity of the topographic (cochleotopic) fre quency map in primary auditory cortex and a restricted or patchy plast icity in the auditory midbrain. This effect is similar to the plastici ty of topographic maps of the sensory surface seen in visual and somat osensory cortices after restricted damage to the appropriate receptor surface in these sensory systems. There is dispute about the extent to which subcortical effects contribute to cortical plasticity. Here, we have examined whether topographic map plasticity similar to that seen in the auditory cortex and the midbrain is observed in the adult audi tory brainstem. When partial cochlear lesions were produced in the sam e manner as those that were produced in the cortex and midbrain studie s, we found no plasticity of the frequency map in the dorsal cochlear nucleus (DCN). Small regions of the DCN that were deprived of their no rmal, most sensitive frequency (characteristic frequency; CF) input by the cochlear lesion appeared to have acquired new CFs at frequencies at or near the edge of the cochlear lesion. However, examination of th resholds at the new CFs established that the changes simply reflected the residue of prelesion input to those sites: The patterns of CF thre sholds were very well predicted by simple calculations of the patterns that were expected from such residual input. The results of this stud y suggest that the DCN does not exhibit the type of plasticity that ha s been found in the auditory cortex and midbrain; therefore, it does n ot account for the changes in responsiveness observed in the higher le vel structures under similar experimental conditions. J. Comp. Neurol. 399:35-46, 1998. (C) 1998 Wiley-Liss, Inc.