Worse Hearing in Middle Age Linked to Brain-Volume Loss

By Reuters Staff

July 12, 2019

NEW YORK (Reuters Health) - Hearing impairment (HI) in middle age is associated with loss of temporal-lobe volume, new research shows.

"These findings support the hypothesis that midlife HI may be a risk factor for dementia in older adults via changes in brain structures," Dr. Susan M. Resnick of the National Institute on Aging in Baltimore, Maryland, and colleagues write in JAMA Otolaryngology-Head and Neck Surgery, online July 3.

Hearing impairment is associated with Alzheimer disease (AD), the authors note. Proposed pathways for the association include "cognitive load from reallocation of brain structures for auditory processing, change in brain structure and function, and decreased social engagement," they add.

The authors looked at 194 participants in the Baltimore Longitudinal Study on Aging who had their hearing assessed at age 54.5 years, on average, and underwent brain MRI in 2008-2015. Follow-up lasted a mean 19.5 years.

Worse hearing in a person's better ear was associated with greater declines in right temporal gray matter, right hippocampus and the left entorhinal cortex, Dr. Resnick and colleagues found. Worse hearing in the right ear was also associated with declines in the volume of these brain structures, as well as the right temporal pole.

There was no association between midlife hearing in the left ear and changes in brain tissue volumes.

The right hippocampus and left entorhinal cortex are affected in the early stages of AD, the authors note.

"These findings suggest that HI could affect temporal lobe structures, producing cascading effects on neighboring structures implicated in cognitive impairment. Age-related HI can result in poorer encoding of sound by the cochlea," they add. "As a consequence, poor auditory signals and reduced stimulation from the impaired cochlea may produce changes in cortical organization and brain morphometry."

They conclude: "The variety of mechanisms that may underlie the association between HI and subsequent late-life brain volume loss merit further investigation."

Dr. Resnick was not available for an interview by press time.

SOURCE: https://bit.ly/2NLTejD

JAMA Otolaryngol Head Neck Surg 2019.

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