Mapping the Human Subcortical Auditory System With MRI

Abstract

The subcortical auditory system comprises multiple neural structures that perform important functions in speech communication, music perception, and general auditory processing. However, investigating the deep, small subcortical auditory structures in humans is challenging with current non-invasive methods such as magnetic resonance imaging, or MRI. One major difficulty is in identifying the subcortical auditory structures in vivo. To address this challenge, collaborators and I created atlases of the human subcortical auditory system using gold-standard histology, post mortem anatomical MRI, and state-of-the-art in vivo functional MRI. We registered each of these atlases to a common MRI reference space to facilitate future research in these regions. Then, with diffusion-weighted MRI tractography both post mortem and in vivo, we estimated the structural connections between these subcortical auditory structures, providing us with a 3-dimensional auditory connectivity map. I next tested the applicability of our reference space atlases by estimating functional and diffusion-weighted connectivity in the freely available Human Connectome Project 7-Tesla MRI data set. I found that resting state functional connectivity was greater between the subcortical auditory regions than to nearby control regions. Likewise, diffusion tractography supported expected connectivity estimates between the subcortical auditory structures. These analyses suggest that our histology, post mortem MRI, and in vivo functional MRI atlases successfully identify the subcortical auditory structures in novel in vivo participants. Finally, we sought to describe the physical characteristics of the subcortical auditory system with quantitative MRI. Using a multi-parametric mapping protocol, we quantified MRI relaxation and proton density values in the auditory structures of five individuals over two sessions each, contributing novel information about the makeup of these regions. In total, my work has used state-of-the-art techniques to identify the human subcortical auditory structures, applied our knowledge to new data, and quantitatively described the magnetic response properties of the subcortical auditory system. By releasing our data and tools publicly, we hope to foster further research into the role of the subcortical auditory structures in human hearing and communication.