Ramadhani, Anissa Lintang
(2025)
Using neuroimaging to investigate central auditory changes following hearing loss and tinnitus.
PhD thesis, University of Nottingham.
Abstract
Tinnitus, a condition characterized by the perception of phantom sounds, affects a significant portion of the population, often in conjunction with hearing loss. Despite its prevalence, the underlying mechanisms of tinnitus remain elusive, with central auditory processes believed to play a crucial role. This thesis explores the central mechanisms involved in tinnitus, focusing on brain plasticity models—cortical reorganization and homeostasis—as potential explanations for the onset and persistence of tinnitus in humans.
The research presented in this thesis comprises three neuroimaging studies employing advanced techniques such as structural magnetic resonance imaging (MRI), functional MRI, diffusion MRI, and magnetic resonance spectroscopy (MRS) to investigate brain structural and functional changes associated with hearing loss and tinnitus. The first study, using MRS, assessed the feasibility of quantifying gamma-aminobutyric acid (GABA) levels in the auditory cortex, revealing challenges in detecting significant changes in this key inhibitory neurotransmitter, which may play a role in tinnitus perception.
The second study, leveraging data from the UK Biobank, examined structural plasticity in central auditory structures, identifying small yet significant effects of hearing loss on brain structure, particularly in auditory white matter tracts. The study also found that tinnitus interacts with hearing loss, moderating structural integrity, with implications for understanding the preservation of brain health in the context of sensory deprivation.
The third study employed resting-state fMRI to investigate the effects of tinnitus on spontaneous neural activity. By using a functional analogy that compared the resting brain activity of individuals with and without tinnitus, the study simulated the persistent auditory experience of tinnitus with continuous acoustic stimulation. The results demonstrated that tinnitus is associated with increased spontaneous activity fluctuations in auditory-related regions, particularly at smaller spatial scales, and revealed that the coherence of spontaneous fluctuations decreased, particularly at larger spatial scales, during task conditions compared to rest, suggesting a reorganization of neural activity that may enhance information processing during auditory tasks.
The final study, using functional MRI, focused on spontaneous and stimulus- evoked tonotopy response within the auditory cortex, to compare individuals with normal hearing and high-frequency hearing loss, with and without tinnitus. The findings indicate that tinnitus is associated with increased spontaneous activity fluctuations, and enhanced evoked responses within the deprived high-frequency areas to non-preferred stimulus frequencies near the hearing loss edge, or slope, suggesting cortical reorganization and homeostatic changes occurred together within the deprived area within the auditory region.
Together, these studies advance our understanding of the central mechanisms underlying tinnitus and hearing loss, highlighting the complex interplay between cortical reorganization and homeostasis. This work contributes to the broader field of sensory neuroplasticity, offering new insights into the brain’s adaptive responses to hearing loss and the resulting phantom perceptions.
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