Title : Alignment of Sound Localization Cues in the Nucleus of the Brachium of the 1 Inferior

23 24 Accurate sound localization is based on three acoustic cues (interaural time and intensity 25 difference, and spectral cues from directional filtering by the pinna). In natural listening 26 conditions, every spatial position of a sound source provides a unique combination of 27 these 3 cues in “natural alignment”. Although neurons in the central nucleus of the 28 inferior colliculus (ICC) are sensitive to multiple cues, they do not favor their natural 29 spatial alignment. We tested for sensitivity to cue alignment in the nucleus of the 30 brachium of the IC (BIN) in unanesthetized marmoset monkeys. The BIN receives its 31 predominant auditory input from ICC and projects to the topographic auditory space map 32 in the superior colliculus. Sound localization cues measured in each monkey were used to 33 synthesize broadband stimuli with aligned and misaligned cues; spike responses to these 34 stimuli were recorded in the BIN. We computed mutual information (MI) between the set 35 of spike rates and the stimuli containing either aligned or misaligned cues. The results 36 can be summarized as follows: 1) BIN neurons encode more information about auditory 37 space when cues are aligned compared to misaligned. 2) Significantly more units prefer 38 aligned cues in the BIN than in ICC. 3) An additive model based on summing the 39 responses to stimuli with the localization cues varying individually accurately predicts 40 the alignment preference with all cues varying. Overall, the results suggest that the BIN is 41 the first site in the ascending mammalian auditory system that is tuned to natural 42 combinations of sound localization cues. 43 44