Neural mechanisms for spatial processing in marmoset auditory cortex

Johns Hopkins University, Baltimore MD

Investigators

Abstract

? DESCRIPTION (provided by applicant): Sound localization is a crucial ability for survival and navigation in the environment. In the mammalian brain, the auditory cortex (AC) is shown to be necessary for localization behavior and plasticity. There has long been the notion that sound identity and location information may be processed in separate pathways in AC, similar to the dorsal and ventral pathways in the visual system. Divergence of these pathways is said to begin from the connections projecting from AC core to belt. The 'what' pathway is thought to be located rostrally in lateral belt since response to vocalizations is stronger in this region, wheres the 'what' pathway extends caudally as neurons show sharp spatial tuning. The caudolateral (CL) area in belt has shown the most refined spatial tuning compared to the core AC and the rostral belt areas. In fact, a gradient for spatial selectivity has been reported along the rostrocaudal axis, being most selective caudally and least selective rostrally. However, there are major knowledge gaps regarding functionality of CL as a specialized center for sound location processing. First, it is not known to what extent CL refines spatial selectivity, since past works have focused on azimuth tuning in front of animals. If CL is indeed functionally specialized for sound localization, we would expect elevation tuning to be processed similarly to azimuth for regions all across auditory space. In Aim 1, I will test if selectivity in elevation also increases rostrocaudally in lateral belt. In awake marmosets, I will compare spatial tuing in CL and anteriorlateral belt area (AL) using virtual acoustic space stimuli to test if spatial selectivity s more refined in CL neurons across auditory space, including areas above, below and behind the animal. Second, it is not clear what mechanisms confer the difference in spatial selectivity between CL and AL. In Aim 2, I will use intracellular recording in awake marmosets to test if there is already a difference in spatial tuning in the inputs to AL and CL neurons, or if there is difference in intrinsic integration mechanisms along the rostrocaudal axis within the lateral belt. These aims will bring us closer to understanding the role of auditory cortex in sound localization. The questions addressed by this study are pertinent to sound localization mechanisms in a non-human primate and are compatible with the mission of the National Institute on Deafness and Other Communication Disorders (NIDCD) to study hearing in normal and diseased conditions.