Analysis of temporal discharge characteristics of dorsal cochlear nucleus neurons of unanesthetized decerebrate cats.

1. We examined the mean and standard deviation (SD) of interspike intervals (ISI) and the coefficient of variation (CV, the ratio of SD of ISI to mean ISI) of ISIs versus time to study discharge regularity of units in the dorsal cochlear nucleus (DCN) of decerebrate unanesthetized cats. The units were characterized by the use of both poststimulus time histograms (PSTH) and excitatory-inhibitory area (EI-area) schemes. We present results of a systematic examination of all of 87 DCN pause-build units recorded in this study. In addition, we present examples of chopper subtypes of the DCN. 2. A major finding of this study is that a majority of the pause-build units in the present sample exhibited regular discharges in response to short (50 ms) tone bursts at characteristic frequency (CF), as revealed by CVs less than 0.5. A predominant portion of pause-build units (80% of 44 units with sufficient number of spikes for CV analysis) exhibited mean CVs less than 0.5 in the 20- to 39.9-ms time window in response to 50-ms tone burst at CF at 60 dB SPL re 20 microPa; 39% of the 44 units exhibited highly regular discharges (mean CV less than 0.35). During the onset (2-14.9 ms) time window, 77% (of 53 units with sufficient number of spikes for CV analysis) of the units had mean CVs less than 0.5, and 55% were less than 0.35. 3. In our sample of 87 DCN pause-build units, 59% had spontaneous rates (SR) greater than 15 spikes/s. The pause-build units of the present sample were distributed across four different EI-area types: III (51%), I/III (25%), II (15%), or IV (9%). In the 20- to 39.9-ms time window, the pause-build units with mean CVs less than 0.35 were exclusively of types III and I/III. All of the above EI-area types were represented in the lowest CV group for the 2- to 14.9-ms window. 4. The mean ISIs of DCN pause-build units typically showed a decrease during the first 20-25 ms of the response to 50-ms CF tone bursts, and stable mean ISIs in the latter half, when off-discharges were absent. In the presence of off-discharges, the mean ISIs decreased further in the last 5-10 ms of the response.(ABSTRACT TRUNCATED AT 400 WORDS)