A groundbreaking study published in Neurobiology of Aging examines how measures of cognition and hearing covary with specific features of the hippocampus identified through structural magnetic resonance imaging in both younger and older adults. Led by Imola X. MacPhee along with co-authors Josh Goheen, Melanie J. Sekeres, Shanna Kousaie, and John A.E. Anderson, the research provides new insights into the neural mechanisms linking sensory and cognitive functions across the adult lifespan.
The work builds on established connections between hippocampal changes, cognitive performance, and auditory processing. Researchers recruited 26 younger adults aged 18 to 30 and 19 older adults aged 60 and above, all cognitively healthy individuals from Ottawa, Canada. Participants underwent comprehensive assessments including pure tone audiometry and the QuickSIN test for hearing in noise, cognitive evaluations with the Montreal Cognitive Assessment and Shipley-2, and 3T structural MRI scans focused on T1-weighted images.
Background on Hippocampal Subfields and Lifespan Changes
The hippocampus plays a central role in memory formation and spatial navigation, yet it comprises distinct subfields such as the subiculum, CA1, CA3, and CA4, each with specialized functions. Prior research has shown that overall hippocampal volume tends to decline with advancing age, often correlating with reduced cognitive abilities. Hearing difficulties, particularly challenges understanding speech amid background noise, have also been associated with broader brain changes. This study extends that knowledge by focusing on subfield-specific features rather than total volume alone.
Using the HippUnfold tool, a machine-learning approach for automated hippocampal unfolding and subfield segmentation, the team analyzed fine-grained structural details. This method allows precise mapping that traditional volume measurements might overlook, revealing how individual subregions relate differently to hearing and cognitive variables.
Study Methods and Analytical Approach
Data collection combined behavioral testing with neuroimaging in a cross-sectional design comparing two age groups. Multiple linear regression examined total hippocampal volume in relation to age and hearing metrics. For the more nuanced subfield analysis, researchers applied Multiple Factor Analysis, a multivariate technique that reduces data dimensionality while examining relationships across blocks of variables including brain measures, age, hearing performance, and cognitive scores.
This approach generates principal components, or dimensions, that highlight the strongest covariations. Preliminary analyses also explored hearing thresholds specifically within the older adult group to identify age-specific patterns.
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Key Findings on Volume and Subfield Associations
Total hippocampal volume showed the expected reduction with increasing age and greater hearing difficulty, with statistical support from an F-statistic of 5.97 and p-value of 0.005. The first dimension from the Multiple Factor Analysis accounted for 23 percent of the variance and prominently featured contributions from the subiculum, CA1, and CA4 subfields. These brain features aligned closely with age, performance on the QuickSIN hearing-in-noise test, and Shipley-2 cognitive scores.
A second dimension explained 11 percent of the variance and was driven primarily by age alongside CA3 subfield characteristics. In exploratory analyses restricted to older adults, one dimension was dominated by age explaining 25 percent of variance, while another linked cognition via MoCA scores, left-ear hearing thresholds, sex, and left hippocampal subfield measures, accounting for 18 percent of variance.
These results mark the first reported associations between specific subfields—the subiculum, CA4, and CA1—and combined hearing and cognitive measures in humans. Animal studies had previously suggested tonotopic organization in CA1, but human data on this topic remained limited until now.
Implications for Understanding Sensory-Cognitive Interactions
The findings suggest that hearing-related challenges may influence or reflect structural variations in particular hippocampal subregions that also support cognitive functions. This integrated view could help explain why interventions targeting hearing sometimes yield cognitive benefits, or vice versa. The framework proposed in the study offers a pathway to evaluate how hearing aids or auditory training programs might affect brain structure and function over time.
Because the sample included both younger and older adults, the research highlights lifespan patterns rather than isolating age-related decline. Differences in subfield involvement between age groups point to potentially distinct mechanisms at play during different life stages.
Future Directions and Broader Context
Researchers note that larger, longitudinal studies will be needed to establish causality and track changes over time. Incorporating additional modalities such as functional MRI or diffusion imaging could further clarify the roles of these subfields. The work also opens avenues for investigating whether early hearing interventions might preserve hippocampal integrity and support cognition into later life.
Given the global rise in both age-related hearing loss and cognitive concerns, studies like this contribute valuable evidence for public health strategies. Institutions and clinicians may eventually use subfield-specific biomarkers to personalize approaches for individuals experiencing combined sensory and memory difficulties.
Read the original publication here: https://www.sciencedirect.com/science/article/pii/S0197458026001168
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Expert Perspectives and Research Momentum
Lead author Imola X. MacPhee, a PhD student and audiologist at Carleton University, brings expertise bridging auditory science and cognitive neuroscience. Collaborators from related fields strengthen the interdisciplinary nature of the project. The publication arrives amid growing interest in how sensory health intersects with brain aging research worldwide.
Academic communities are increasingly recognizing the value of such integrated studies for informing both basic science and applied interventions. This paper adds concrete data to ongoing discussions about modifiable risk factors for cognitive health.
