Hearing the Unheard: Novel Ear Test Hints at Early Cognitive Decline Risk

Cochlear Dysfunction: A Clue to Early Cognitive Decline

A team of researchers from the University of Chile and other institutions have identified a possible early indicator of cognitive decline in older adults with normal hearing or mild hearing loss. The study, published in "Alzheimer's & Dementia: Diagnosis, Assessment & Disease Monitoring," focuses on what's known as Distortion Product Otoacoustic Emissions (DPOAEs), a byproduct of sound waves in the ear that may offer insight into the risk of cognitive decline.

Understanding the Study

The international team of researchers, including Vicente Medel and Paul H. Delano, conducted a study involving 94 individuals over the age of 64. They aimed to investigate the relationship between cochlear dysfunction, measurable via DPOAEs, and cognitive decline, as indicated by neuropsychological assessments and brain magnetic resonance imaging (MRI).

Age-related hearing loss is recognized as an important risk factor for cognitive decline. However, audiogram thresholds—the typical measurements taken to estimate hearing loss—are not sufficient to estimate the risk of dementia in those with normal or mildly impaired hearing. The discovery suggests that DPOAEs could serve as a more sensitive tool to detect early signs of neurodegeneration, potentially leading to timely interventions that could slow down or prevent further cognitive decline.

Explaining DPOAEs

DPOAEs are essentially sounds that are emitted by the outer hair cells in the cochlea of the ear when it is functioning normally. Until now, hearing impairments have been estimated with subjective methods, such as traditional audiometer tests. In contrast, DPOAEs are an objective method and can indicate the health of these hair cells, which are vital to our ability to hear. The loss of these emissions points to cochlear dysfunction, even when standard hearing tests show normal results.

The Link Between Hearing and Cognitive Function

A growing body of research suggests that hearing impairment and cognitive decline are closely linked. Hearing loss, particularly when moderate to severe, has been associated with an increased risk of all-cause dementia. However, this new research indicates that even mild hearing loss (25 to 40 decibel range) or those with normal hearing thresholds (below 25 decibels) may be at risk. The study highlights that certain cochlear or auditory processing disorders not detected by conventional hearing tests, such as hidden hearing loss, could also be associated with cognitive issues in older adults.

Key Findings

By assessing the presence of DPOAEs and independently evaluating participants' cognitive profiles, the researchers found that cochlear dysfunction, as measured by DPOAEs, was linked with worse scores on the Clinical Dementia Rating Sum of Boxes (CDR-SoB), a scale used to evaluate dementia. Moreover, brain atrophy, particularly in regions not directly related to hearing, correlated with the loss of DPOAEs, suggesting broader neurodegeneration at play.

Breaking New Ground

Prior research had already observed significant associations between reduced DPOAEs and atrophy in various non-auditory brain regions, such as the cingulate cortex, insula, and amygdala. These structural changes in the brain have been related to impairments in cognitive and behavioral domains, including recognition of faces and executive function. This study builds on those findings by connecting these cognitive and behavioral impairments more directly with clinical indicators of cognitive decline and dementia.

Implications for the Future

The successful identification of DPOAEs as a biomarker for cognitive decline holds great promise for the future of dementia prevention and treatment. Early detection can lead to early intervention, which may include lifestyle adjustments, therapeutic strategies, or other preventative measures tailored to preserve cognitive health. This research underscores the value of monitoring cochlear health as part of routine checks in older adults, especially for those with hearing within normal ranges or with mild hearing impairment.

About the Study

The study was led by experts from the University of Chile, with contributions from related institutes such as Latin American Brain Health Institute, the Biomedical Neuroscience Institute, and others. It was funded by several grants from the National Agency for Research and Development of Chile, showcasing the country's commitment to advancing research in cognitive health and neurodegeneration.

In conclusion, this study advances our understanding of cognitive decline and dementia, proposing a novel method—measuring cochlear dysfunction through DPOAEs—to detect early signs of cognitive changes. This approach may revolutionize how we identify individuals at risk for neurodegenerative diseases, potentially leading to interventions that could substantially alter the trajectory of such conditions.