A mammalian inferior colliculus model for sound source separation using interaural time differences

The inferior colliculus (IC) hosts many neurons tuned to interaural time differences (ITDs) at low frequencies. ITD tuning, however, is already observed and generated in the superior olivary complex. Here, we argue that combining ITD sensitive inputs from medial superior olive (MSO) and low-frequency lateral superior olive (LSO) requires a temporally well adjusted delay of commissural fibers from LSO to IC, given the fast synaptic kinetics of IC neurons. We present a normative model of the midbrain auditory circuitry that finds an optimal commissural delay of 0.3 cycles and optimal synaptic strengths by maximizing the firing rate of IC neurons for a given ITD. The model suggests that, by varying the relative synaptic weight of MSO and LSO input, individual neurons are optimized to transmit information for any sound source in complex auditory scenes. ITD tuning of IC neurons results as a side effect and follows the statistics known from experimental recordings.