Auditory Processing in the Brainstem and AudioVisual Integration in Humans Studied with fMRI

Abstract

This thesis discusses the application of functional magnetic resonance imaging (fMRI) to the auditory system in the human brain. The main goal of this research is a better understanding of the auditory subcortical mechanisms. Chapter 2 describes recent fMRI/MRI studies on the human central auditory pathway, emphasizing anatomical, methodological, technical issues, and applications to the brainstem. Chapters 3 and 4 describe the effects of slice orientation on the inferior colliculi, superior olivary complex, and cochlear nucleus. Using fMRI we detect differences on the activation cluster for the inferior colliculi. Our results indicate that the imaging plane at 45 degrees to the brainstem has the lowest sensitivity to motion (reflected in the standard deviation and normalized standard deviation) and offers the highest spatial accuracy for the inferior colliculi and auditory cortex. The orthogonal slice orientation offers the highest effect size but with a reduced spatial specificity. Chapter 5 describes experiments on audiovisual integration in speech perception. These address the sensitivity of subjects for certain combination of audio-visual speech stimulus information Tomaskovic, 2006. The first chapter briefly introduces concepts that are used in the thesis: physical principles of MRI, fMRI and Blood Oxygen Level Dependant (BOLD) signal, auditory and visual processing, and a brief description of brain anatomy.