Abstract
Age related hearing loss (presbycusis) is a natural process represented by elevated auditory thresholds and decreased speech intelligibility, especially in noisy conditions. Tinnitus is a phantom sound that also potentially leads to cortical changes, with its highest occurrence coinciding with the clinical onset of presbycusis. The aim of our project was to identify age, hearing loss and tinnitus related structural changes, within the auditory system and associated structures. Groups of subjects with presbycusis and tinnitus (22 subjects), with only presbycusis (24 subjects), young tinnitus patients with normal hearing (10 subjects) and young controls (17 subjects), underwent an audiological examination to characterize hearing loss and tinnitus. In addition, MRI (3T MR system, analysis in Freesurfer software) scans were used to identify changes in the cortical and subcortical structures. The following areas of the brain were analyzed: Heschl gyrus (HG), planum temporale (PT), primary visual cortex (V1), gyrus parahippocampus (PH), anterior insula (Ins), amygdala (Amg), and hippocampus (HP). A statistical analysis was performed in R framework using linear mixed-effects models with explanatory variables: age, tinnitus, laterality and hearing. In all of the cortical structures, the gray matter thickness decreased significantly with aging without having an effect on laterality (differences between the left and right hemispheres). The decrease in the gray matter thickness was faster in the HG, PT and Ins in comparison with the PH and V1. Aging did not influence the surface of the cortical areas, however there were differences between the surface size of the reported regions in the left and right hemispheres. Hearing loss caused only a borderline decrease of the cortical surface in the HG. Tinnitus was accompanied by a borderline decrease of the Ins surface and led to an increase in the volume of Amy and HP. In summary, aging is accompanied by a decrease in the cortical gray matter thickness; hearing loss only has a limited effect on the structure of the investigated cortical areas and tinnitus causes structural changes which are predominantly within the limbic system and insula, with the structure of the auditory system only being minimally affected.
Highlights
IntroductionAge related hearing loss (presbycusis) and subjectively perceived phantom sound (tinnitus) are two of the most common hearing related pathologies
Age related hearing loss and subjectively perceived phantom sound are two of the most common hearing related pathologies
If the audiograms fell within twice the standard deviation (2 × SD) borderline, they were considered physiologic (Y-NH-no tinnitus (NT), Y-NH-T, aged group with mild presbycusis (O-NH-NT), and aged group with tinnitus and mild presbycusis (O-NH-T)), if they were outside the 2 × SD borderline the hearing pathology was considered expressed (O-HL-NT and aged group with tinnitus and expressed presbycusis (O-HL-T))
Summary
Age related hearing loss (presbycusis) and subjectively perceived phantom sound (tinnitus) are two of the most common hearing related pathologies. Hearing deterioration can begin as early as the age of 30, it starts to manifest itself as high frequency hearing loss and worsened speech perception at around the age of 60 (Gates and Cooper, 1991), affecting ∼30% of the population (Lin et al, 2011). Tinnitus prevalence in the population is estimated to be around 2–3% and varies with age (Bhatt et al, 2016), reaching ∼15% in the 7th decennium (Shargorodsky et al, 2010). 90% of patients with chronic tinnitus suffer from clinically relevant sensorineural hearing loss (SNHL) (Adrian and Refaie, 2000). A high number of patients with SNHL never develop tinnitus
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