Brain stem mechanisms for sound localization: Monaural and binaural pathways to the inferior colliculus

The current view that the medial and lateral superior olives have binaural functions related to localization of sound in space grew, in part, from observations on the ascending connections to these nuclei. The anteroventral cochlear nucleus is the origin of the major projections to these nuclei, which in turn, project as a “binaural pathway” to the inferior colliculus. Because the anteroventral cochlear nucleus is also the source of a “monaural pathway” to the contralateral inferior colliculus, the question arises as to whether or not these two pathways overlap at the inferior colliculus. Our anatomical evidence shows that these two pathways converge in the lateral part of the central nucleus of the inferior colliculus of the tree shrew. Observations on these pathways in other mammals suggest that this convergence is a general feature in mammalian auditory pathways. Behavioral evidence suggests that both binaural and monaural pathways are important for localization of sound in space. [Supported by grants from NIH and NSF.]