Bilateral integration of the auditory scene

ABSTRACT The auditory system is posed with answering a challenging question: Does sound arriving at each ear originate from a single source or multiple sources? To accomplish this perceptual feat, central auditory neural circuits must accurately assess the spectral and temporal profile of bilateral sound signals to bind and integrate related acoustic objects. Failure of this bilateral integrative process can account for many of the perceptual and behavioral impairments that accompany auditory disorders, such as tinnitus, presbycusis and central auditory processing disorders, which most of the population will experience over the lifespan. Surprisingly, the neural mechanisms that enable this bilateral integration of acoustic information remain largely unknown, but likely depend on an intricate balance of excitatory and inhibitory connections that link the two halves of the auditory brain. Although commissural pathways have been well studied in auditory brainstem centers, much less is known about the functional organization of commissural circuitry in higher centers of the auditory brain. Thus, the long- term goals of our research are to understand the functional organization of the commissural pathways in the processing of bilateral auditory information. Our primary objective here is to test a largely overlooked, yet substantial, commissural auditory projection system, i.e. the pathway from the inferior colliculus to the contralateral medial geniculate body. Our central hypothesis is that the medial geniculate body integrates functionally and topographically aligned inputs from both the ipsilateral and contralateral inferior colliculi at a cell- type specific level. Further, we hypothesize that the disruption of such bilateral tectothalamic convergence results in deficits to the spectral and temporal processing of acoustic information in the medial geniculate body, which contributes to disorders of the central auditory system. We will test our hypotheses by assessing: 1) the functional neuroanatomy and 2) the neurophysiological impact of these contralateral tectothalamic pathways on auditory processing, by employing modern, cell-type specific neuroanatomical and neurophysiological approaches. As such, these studies are innovative since they address the unknown and unexplored functional organization of the contralateral auditory tectothalamic pathways. Finally, the proposed experiments are significant since they are expected to reveal mechanistic features of auditory processing that will have a positive impact for neural diagnostics and treatments for central auditory impairments.