MARGINAL SHELL OF THE ANTEROVENTRAL COCHLEAR NUCLEUS - SINGLE-UNIT RESPONSE PROPERTIES IN THE UNANESTHETIZED DECEREBRATE CAT

Marginal shell of the anteroventral cochlear nucleus: single-unit resp onse properties in the unanesthetized decerebrate cat. J. Neurophysiol . 77: 2083-2097, 1997. The marginal shell of the anteroventral cochlea r nucleus (AVCN) is anatomically different from its central core. We i nvestigated 38 single units in the shells of 10 cats and contrasted th em with 62 single units in the cores of 15 cats. The sites of all shel l units were localized with the use of reconstructed electrode tracks. The shell units were divided into acoustically well-driven (68%) and weakly/not-driven (32%) subgroups. The shell units mostly exhibited lo w spontaneous rates (SRs). Among the well-driven shell units, a large majority (68%) exhibited wide dynamic ranges (greater than or equal to 50 dB) to tones, noise, or both, with some ranges as wide as 89 dB. I n contrast, a large majority (80b) of the core units exhibited narrow dynamic ranges (<50 dB) to tones and noise. The poststimulus time hist ograms (PSTHs) of the well-driven shell units included pause-build (29 %), onset (24%), and unusual (33%) types, whereas those of the core un its included mainly primarylike (47%) and chopper (29%) types. The exc itatory-inhibitory areas (EIAs) of the well-driven shell units include d types I/III (47%), III (22%), IV (13%), and II (9%), whereas those o f the core units included mainly types III (52%) and I/III (32%). On t he basis of Fisher's exact tests, we conclude that the shell and core neural groups of the AVCN are significantly different regarding all of the following physiological characteristics: SR, maximum driven rate, threshold and dynamic range to tones and noise, frequency response ar ea, PSTH type, latency, and EIA type. Wide dynamic ranges of the well- driven shell units suggest that they may play a role in encoding absol ute intensity of acoustic stimulus.