Modelling convergent input onto interaural-delay-sensitive inferior colliculus neurones

Convergent input from cells in the medial superior olive (MSO) and lateral superior olive (LSO) onto a single inferior colliculus (IC) cell explains m any findings that are not compatible with a simple coincidence detector mec hanism. Here this explanation is tested using a physiologically accurate co mputer model of the binaural pathway in which the input to the IC cell is e ither from two MSO cells or a MSO and a LSO cell. Auditory nerve (AN) spike trains are formed by a stochastic hair cell model following a basilar memb rane simulation using a gammatone filter. In subsequent cells input spikes cause post-synaptic potentials (PSPs) which are summed causing the cell to fire when the stun crosses a threshold. The individual cells are matched to the physiology by varying the number of inputs, the magnitude and duration of the PSPs and the firing threshold. Non-linear best-phase-versus-frequen cy functions arise if the two IC inputs have different best frequencies and different characteristic delays. One input can be selectively suppressed b y turning on an additional tone at the worst phase of that input. Non-zero characteristic phases arise if the characteristic frequencies of the AN fib res feeding into a single superior olive cell are mismatched. (C) 2000 Else vier Science B.V. All rights reserved.