PULSE-RATE DEPENDENT INTEGRATION OF ITD AND ILD CUES IN THE MOUSE AUDITORY MIDBRAIN

Mice are gaining importance as an animal model in auditory research given their suitability for genetic techniques, but how suitable they are for studying binaural hearing remains uncertain. Here, we investigated the integration of interaural time (ITD) and level (ILD) differences in the mouse inferior colliculus (IC) with acoustic pulse (click) trains of varying rates. Multiunit activity was recorded using 64-channel silicon electrodes. At 100 pulses per second (pps), most units with frequency selectivity are tuned to both ITD and ILD, predominantly exhibiting monotonic increasing tuning shape that favor the contralateral stimulus. At 900 pps, ILD tuning remained robust with similar monotonic tuning, whereas ITD tuning significantly decreased, with more neurons showing peaked tuning centered near 0 ITD. Nearly all units were excited by contralateral and inhibited by ipsilateral stimulus (E/I) or monaurally excited by the contralateral side (E/O). A small subset of neurons showed shifts in their tuning peaks when both cues were varying, indicating an ITD/ILD cue interaction. ITD sensitivity declined for pulse rates above 500 pps and and phase-locking above 300 pps. Like other previous studies, we therefore found widespread and robust ILD sensitivity, but in addition, at low pulse rates, we also observed a fair amount of ITD sensitivity as well as synergistic interactions between ITD and ILD cues in a subset of neurons.