Role of connectivity between hippocampus and auditory cortex in adverse listening conditions

This project investigates the role of the hippocampus (HC) in adverse listening conditions in human subjects using high resolution 7 Tesla functional magnetic resonance imaging (fMRI). Although HC has traditionally been studied predominantly as a visuospatial processor, evidence is emerging that it plays an important role also in auditory processes that support speech and communication, including comprehension of degraded speech. However, a comprehensive model of how the interplay between the HC and auditory cortex relate to auditory cognition is still lacking. One potential way to address this question is to use 7T fMRI, which allows for recording functional brain activity at sub-millimeter spatial resolution. 7T fMRI thus allows us to investigate not only small structures, such as the HC, but also the activity of different layers of cortex. This is a significant benefit, and recent high-resolution fMRI studies have shown that the layer-specific activity profiles can inform about hierarchical feedforward and feedback influences between brain regions. In this NIDCD Early Career Research (ECR) Award (R21) proposal, we will identify hierarchical processes related to comprehending degraded speech by characterizing cortical layer-specific connectivity between the HC and the auditory cortex. Our hypothesis is that the HC provides feedback to the auditory cortex during listening of degraded speech, and that the feedback increases with contextual information. We test this hypothesis by using different levels of degraded speech with contextual information as stimuli, and quantify the connectivity between HC and auditory cortex as a function of amount of expected feedback to the auditory cortex. We will also correlate the strength of this connectivity with behavioral audiological measures. We expect that this project will yield novel information of the hierarchical relationship between the HC and the auditory cortex in healthy human subjects. Furthermore, it has been suggested that the impaired connection between HC and auditory cortex could be related to the pathology of age-related hearing loss and Alzheimer’s disease (AD). Thus, understanding the role of the HC in auditory processing could have important public health implications by providing information of possible mechanisms involved in the progress of age-related hearing loss and AD. The longer-term goal of this proposal is to obtain preliminary data and results towards a subsequent R01 application, which will include participants with age- related hearing loss and/or mild cognitive impairment at high risk for AD.