Model calculations of time dependent responses to binaural stimuli in the dorsal nucleus of the lateral lemniscus.

In a previous paper (Reed and Blum, 1999), we examined the connectional hypotheses put forward by Markovitz and Pollak (1994) to explain the steady-state behavior of cells in the dorsal nucleus of the lateral lemniscus (DNLL). We found that the steady-state outputs of the four major binaural types of cells found in the DNLL (EI, EI/F, EE/I, and EE/FI) could be accounted for by known connectional patterns using only one or two cells per nucleus and quite simple hypotheses on cell behavior. In this study, we examine the time course of DNLL outputs in response to constant, ongoing, monaural or binaural sounds of various intensities. The model auditory nerve fibers ramp up linearly (usually in 2 ms) to full firing and the anteroventral cochlear nucleus cells have primary-like discharge patterns. Fixed time delays of 1 ms at each synapse are included; other time delays are employed when necessary to understand and reproduce specific features of the experimental data. We find that the connectional patterns utilized in our previous study can account for the rich variety of temporal response patterns found experimentally in the DNLL. Our main findings are: (1) all of the four major binaural types of cells can arise from modifications of the basic connectional pattern that produces EI cells; (2) both excitation and inhibition from the ipsilateral lateral superior olive (LSO) are required to understand DNLL responses; (3) pauser behavior can arise either from time delayed inhibition from a DNLL interneuron or by projection from the LSO; (4) two different mechanisms can account for the ipsilaterally evoked onset response; (5) to explain completely the temporal discharge pattern and binaural interactions of EE/FI cells, a projection from the contralateral DNLL via the commissure of Probst is necessary.