Gray matter volume as a mediator of the relationship between age-related hearing and cognitive function

Age-related hearing loss (ARHL) has been increasingly implicated as a contributor to cognitive decline, yet the structural neural mechanisms underlying this association remain unclear. This study investigates the relationship between hearing function, measured by pure-tone thresholds (PTT) and words-in-noise (WIN) recognition, and gray matter (GM) volume in auditory and non-auditory brain regions in the left and right cerebral hemispheres. We also examine whether GM volume mediates the association between hearing loss and cognitive impairment in a large cohort of 231 healthy adults aged 20-79 years. Structural MRI data were processed using voxel-based morphometry to extract GM volumes in 48 regions of interest (ROIs) selected for their relevance to auditory, cognitive, and attentional processing. Correlation analyses showed significant negative associations between hearing ability (PTT and WIN) and GM volume in Heschl's gyrus, posterior superior temporal gyrus, inferior frontal gyrus, insula, and frontal executive regions. Poorer hearing was also significantly associated with lower cognitive performance as measured by the Montreal Cognitive Assessment (MoCA). Mediation analyses revealed that GM volume partially mediated the relationship between ARHL and cognitive impairment. For PTT scores, 59% of the relationship between hearing and cognitive performance was mediated by GM volume in auditory and non-auditory regions, including the insula. For WIN scores, 25% of this relationship was mediated by combined structural changes in auditory and domain-general brain regions. However, the total effects were small and should be interpreted with caution. These findings suggest that hearing loss is associated with structural changes in auditory and non-auditory brain regions, which may partly explain its link to cognitive decline in aging.