Date of Award

Spring 1-1-2019

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

First Advisor

Anu Sharma

Second Advisor

Kathryn Arehart

Third Advisor

Jerry Rudy

Fourth Advisor

Albert Kim

Fifth Advisor

Melinda Anderson

Abstract

Age-related hearing loss is a leading chronic health condition among adults and has been associated with neurocognitive decline, including dementia. While the causal link between hearing loss and cognitive decline is poorly understood, auditory deprivation may tax the brain, inducing compensatory re-allocation of cortical and cognitive resources. In the long-term, structural and functional brain changes associated with hearing loss may deplete cognitive reserve, precipitating neurocognitive degeneration.

Visual cortical cross-modal re-organization is a form of compensatory neuroplasticity observed in hearing loss, but the mechanisms underlying such brain changes remains unclear. Hearing loss is associated with increased neuronal excitability and decreased inhibition in the auditory cortex, possibly unmasking latent non-auditory connections (resulting in cross-modal plasticity) and altering top-down modulation of attention and cognitive processes. However, it remains unclear how alterations in cortical neuroplasticity relate to cognitive outcomes. Further, clinical treatment effects with hearing aids on visual cortical neuroplasticity in age-related hearing loss has not been investigated. In Study 1, we examined the association between visual cortical neuroplasticity and speech perception and cognitive function in untreated, mild-moderate age-related hearing loss, relative to normal hearing listeners. In Study 2, we evaluated whether hearing aid treatment provided neurocognitive benefit.

Consistent with previous investigations, untreated hearing loss was associated with visual cross-modal re-organization. Greater visual cross-modal re-organization was associated with severity of hearing loss, poorer auditory speech perception abilities, and poorer cognitive function, but not enhanced dependence on visual (lip-reading) cues. Hearing aid treatment reversed cross-modal recruitment of auditory cortex for visual processing over the course of 6 months, coinciding with gains in auditory speech perception abilities and improvements in cognitive performance. Further, pre-treatment visual cross-modal re-organization predicted 6-month post-treatment auditory speech perception outcomes, providing evidence that the functional status of the auditory cortex may limit post-treatment success with hearing aids.

Results of this study provide evidence that hearing aid use may reverse deprivation-induced changes in cortical resource allocation in the auditory cortex and enhance cognitive function in early-stage hearing loss. Further, this study highlights the utility of neurocognitive assessment tools in the audiology clinic for guiding early identification, treatment, and rehabilitation of hearing loss.

Comments

Additional adviser: Christine Brennan

Share

COinS