Cortical thickness of left Heschl's gyrus correlates with hearing acuity in adults – A surface-based morphometry study

To date, research examining the relationship between brain structure and hearing acuity is sparse, especially given the context of a broad age range. To investigate this relationship, we applied an automated surface-based morphometry (SBM) approach (FreeSurfer) in this study to re-examine a sample of normal-hearing (n = 17) and hearing-impaired (n = 17) age- and education-matched adults, aged between 20 and 63 years (Alfandari et al., 2018). The SBM approach allows the disentanglement of cortical surface area (CSA) from cortical thickness (CT), the 2 independent constituents of cortical volume (CV). We extend the findings of Alfandari and colleagues by showing several clusters in auditory-related areas as well as in the left and right angular gyrus that showed reduced CT, CSA and CV in hearing-impaired compared to normal-hearing listeners. Nevertheless, none of the clusters found correlated significantly with hearing acuity, measured by pure-tone thresholds, in the 2 groups. An additional vertex-wise correlation analysis between hearing acuity and morphometric parameters over all participants revealed a single significant cluster encompassing the left Heschl's gyrus. Higher hearing thresholds were associated with a thinner cortex within this cluster. Our results imply that hearing impairment is associated with reduced thickness in primary and secondary auditory cortex regions, those regions especially involved in perceiving and processing relevant speech cues. This decrease was observed not only in older but also in younger and middle-aged adults, independent of age-related decline in the cognitive domain and age-dependent whole-brain atrophy. Further, the results show the value added when considering CV, CT and CSA separately, relative to previous studies which have solely relied on voxel-based morphometry to investigate brain structure and hearing acuity across the lifespan.