Functional changes in the auditory cortex and associated regions caused by different acoustic stimuli in patients with presbycusis and tinnitus

Abstract

Presbycusis and tinnitus are the two most common hearing related pathologies. Although both of these conditions presumably originate in the inner ear, there are several reports concerning their central components. Interestingly, the onset of presbycusis coincides with the highest occurrence of tinnitus. The aim of this study was to identify age, hearing loss, and tinnitus related functional changes, within the auditory system and its associated structures. Seventy-eight participants were selected for the study based on their age, hearing, and tinnitus, and they were divided into six groups: young controls (Y-NH-NT), subjects with mild presbycusis (O-NH-NT) or expressed presbycusis (O-HL-NT), young subjects with tinnitus (Y-NH-T), subjects with mild presbycusis and tinnitus (O-NH-T), and subjects with expressed presbycusis and tinnitus (O-HL-T). An MRI functional study was performed with a 3T MRI system, using an event related design (different types of acoustic and visual stimulations and their combinations). The amount of activation of the auditory cortices (ACs) was dependent on the complexity of the stimuli; higher complexity resulted in a larger area of the activated cortex. Auditory stimulation produced a slightly greater activation in the elderly, with a negative effect of hearing loss (lower activation). The congruent audiovisual stimulation led to an increased activity within the default mode network, whereas incongruent stimulation led to increased activation of the visual cortex. The presence of tinnitus increased activation of the AC, specifically in the aged population, with a slight prevalence in the left AC. The occurrence of tinnitus was accompanied by increased activity within the insula and hippocampus bilaterally. Overall, we can conclude that expressed presbycusis leads to a lower activation of the AC, compared to the elderly with normal hearing; aging itself leads to increased activity in the right AC. The complexity of acoustic stimuli plays a major role in the activation of the AC, its support by visual stimulation leads to minimal changes within the AC. Tinnitus causes changes in the activity of the limbic system, as well as in the auditory AC, where it is bound to the left hemisphere.

The effect of aging, hearing loss, and tinnitus on white matter in the human auditory system revealed with fixel-based analysis

“…Recent findings complement our previous reports about the functional (Fuksa et al, 2022 ) and gray matter (Profant et al, 2020 ) changes within the auditory and limbic systems induced by aging, hearing loss and tinnitus. Our study confirmed higher specificity of the FBA over DTI as regards to white matter changes within the auditory pathway above the IC, in comparison with our older report (Profant et al, 2014 ).…”

“…From a functional standpoint, all three parameters; aging, hearing loss and tinnitus induce changes in the AC, and to a smaller degree also in the parts of the limbic system (Ins and HP; Fuksa et al, 2022 ). The functional engagement of limbic structures within the tinnitus network is further affirmed by the discoveries of De Ridder et al ( 2011 ) and Maudoux et al ( 2012 ).…”

“…We have previously documented functional changes in the limbic system and auditory cortex (Fuksa et al, 2022) associated with tinnitus and presbycusis. Therefore, the primary objective of this study was to examine the relationship between aging, hearing loss, the presence or absence of tinnitus, and their impact on the white matter of connecting tracts.…”

Asymmetries and hemispheric interaction in the auditory system of elderly people

“…A mixed group of older adults with mild and expressed presbycusis with and without tinnitus showed stronger activity in the left AC and less lateralization of activity compared to younger adults with a combined analysis of different acoustic stimulation (words, words in babble, modulated pink noise and babble) (Fuksa et al, 2022 ). However, it is not clear how much this result was affected by tinnitus and presbycusis.…”

Desensitizing nicotinic agents normalize tinnitus-related inhibitory dysfunction in the auditory cortex and ameliorate behavioral evidence of tinnitus

“…Therefore, ACh signaling should be considered an important modulator of excitatory neuronal function in the normal, as well as in pathological auditory pathways ( Roberts et al, 2013 ). For example, tinnitus-related increases in excitability at multiple subcortical and cortical structures may reflect pathological changes in nAChR function ( Norena, 2011 ; Auerbach et al, 2014 ; Ghimire et al, 2020 ; Fuksa et al, 2022 ).…”