How cognition and hearing-related measures covary with hippocampal subfield features from structural MRI in younger and older adults

Hippocampal atrophy across the lifespan is associated with cognitive decline, as is difficulty understanding speech-in-noise. The hippocampus contains subfields with distinct functions, but their involvement in hearing-related differences is unknown. Here, we used HippUnfold, an automated hippocampal unfolding and subfield segmentation method, together with Multiple Factor Analysis (MFA) to examine shared variance across hippocampal structure, hearing-related function, and cognition in younger and older adults. Twenty-six young adults with normal hearing and twenty-four older adults underwent 3 T MRI scanning along with audiological and cognitive assessment. Consistent with prior findings, cross-sectional analyses revealed age-related reductions in total hippocampal volume. Exploratory MFA identified shared dimensions linking speech-in-noise performance, subjective hearing handicap, cognitive measures, and morphometric features of hippocampal subfields. Specifically, shared variance was observed between subiculum and CA1 morphometry, speech-in-noise and subjective hearing handicap, and cognition, with a secondary dimension relating CA2/CA3 thickness and CA3 volume to subjective hearing handicap and cognitive performance. These results demonstrate covariation among auditory processing, cognition, and hippocampal subfield morphology in adulthood and provide a multivariate framework for generating future hypotheses in cognitive aging.