Research at Johns Hopkins University
The brains of all people shrink with age but the brains of people with hearing loss shrink more rapidly – they lose an extra cubic centimeter of brain a year.
Hearing loss is associated with increased risk of dementia, falls, hospitalization and poor mental health.
Researchers at John Hopkins University, in Baltimore, U.S., and the National Institute on Aging, looked at the on-going Baltimore Longitudinal Study of Aging to compare the brains of elderly people with normal hearing and those with impaired hearing. The Baltimore Longitudinal Study of Aging was started in 1958 by the National Institute on Aging to track various health factors in thousands of men and women. Previous research from other studies linked hearing loss with marked differences in brain structure compared to those with normal hearing, both in humans and animals.
In particular, structures that process information from sound tended to be smaller in size in people and animals with impaired hearing. Dr. Frank Lin, an assistant professor at the Johns Hopkins University schools of medicine and public health, says it was unknown, however, whether these brain structural differences occurred before or after hearing loss.
As part of the Baltimore Longitudinal Study of Aging, 126 participants underwent yearly MRI scans to track brain changes for up to 10 years. Each also had physical examinations at the time of the first MRI in 1994, including hearing tests.
At the starting point, 75 had normal hearing, and 51 had impaired hearing, with at least a 25-decibel loss.
After analyzing their MRIs over the following years, Dr. Lin and his colleagues found those participants whose hearing was already impaired at the start of the study had accelerated rates of brain deterioration compared to those with normal hearing. They found that people with impaired hearing lost more than an additional cubic centimeter of brain tissue each year. Those with poor hearing also had significantly more shrinkage in particular regions, including the superior, middle and inferior temporal gyri – brain structures responsible for processing sound and speech. The middle and inferior temporal gyri, for example, also play roles in memory and have been shown to be involved in the early stages of Alzheimer’s disease. “Our results suggest that hearing loss could be another ‘hit’ on the brain in many ways,” Dr. Lin explained. That structures responsible for sound and speech are affected in those with hearing loss was not a surprise, says Dr. Lin.
Hearing loss speeds up brain shrinkage and could lead to dementia, researchers claim.
People with hearing loss lose an extra cubic centimeter of brain tissue every year – this puts them at increased risk of memory loss and even dementia. He explained that shrinkage in those areas might simply be a consequence of an ‘impoverished’ auditory cortex, which could shrink from lack of stimulation. However, he added these structures don’t work in isolation, and their responsibilities don’t end at sorting out sounds and language.
The study also suggested that it is important to address hearing loss quickly.
Dr. Lin said: ‘If you want to address hearing loss well, you want to do it sooner rather than later. If hearing loss is potentially contributing to these differences we’re seeing on MRI, you want to treat it before these brain structural changes take place.
Dr. Lin and his colleagues say they plan to eventually examine whether treating hearing loss early can reduce the risk of other associated health problems.
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