Voids in the gerbil cochlear nucleus: Is there an anatomical substrate for intensity coding?

The presence of voids in the gerbil cochlear nucleus has been reported by Morest et al. [IUPS Satellite Symposium on Hearing Abstract, p. 80 (1986)] and related to some aspects of auditory experience by McGinn and Faddis [Hear. Res. 31, 235–244]. The number, volume density, and void size were investigated in animals of various ages from 18–485 days. These variables were found to increase as a function of age with a maximum volume density of about 1% [Statler et al., ARO Abstracts, p. 209 (1988)]. The spatial distribution of the number of voids in the cochlear nucleus was computed as a function of the incoming neural activity produced by ambient noise over the life of the animal. In a three-dimensional reconstruction, the voids form a contiguous area in the granular layer and posteroventral cochlear nucleus. The anteroventral cochlear nucleus and dorsal cochlear nucleus are spared. The number of voids was found to be a monotonically increasing, negatively accelerated function of the total neural activity. The difference between the void distribution and tonotopic organization of the cochlear nucleus leads to the interesting possibility that the spatial distribution of voids corresponds to the low-intensity portion of the tonotopic regions of the cochlear nucleus and the void distribution reflects an anatomical substrate for intensity coding.