Hearing loss is one of the most common conditions from which older adults suffer. On average, one third of people between the ages of 65 and 74 have hearing damage, and almost half of those over 75 have serious hearing problems.
Especially when it goes untreated, hearing loss has been linked to a multitude of problems, include a negative effect on brain health. And new research suggests that the part of the brain responsible for hearing can actually become reorganized as hearing diminishes, leading to more rapid cognitive decline.
The University of Colorado study
A study performed by researchers at the University of Colorado has revealed that the principles of neuroplasticity–the ability of the brain to adapt and create new connections–has implications for those who suffer from hearing loss. Even with early stage hearing loss, the study showed, the brain begins to assign other functions to that portion of the brain responsible for hearing as frequencies are lost. The researchers looked at people with different types of hearing loss, ranging from mild-moderate auditory damage to profound deafness.
Anu Sharma, a professor in the Department of Speech Language and Hearing Science at UC Boulder, along with her team, conducts studies using electroencephalographic (EEG) recordings of hard of hearing adults and children; Sharma and her team also perform speech perception and cognitive behavioral experiments to learn more about how the brain responds to hearing loss.
EEG recordings are very useful in that they allow researchers to measure the brain’s activity and responses to sound stimulus, by way of multiple tiny sensors placed on the scalp. When sound signals are received, the elicit “brain waves” in the auditory cortex, which is the main center for processing speech and language. “We can examine certain biomarkers of cortical functioning, which tell us how the hearing portion of a deaf person’s brain is functioning compared to a person with normal hearing,” Sharma explained.
The brain’s reaction to hearing loss
The work of Sharma and her team has paid off, revealing some important clues about the link between hearing loss and dementia.
The researchers have found that the parts of the brain that process vision and touch can begin to take over areas where hearing normally occurs, but which receive little stimulation due to hearing loss. This change is known as “cross-modal” cortical reorganization and is an example of the way the brain evolves in reaction to its environment. “We find that this kind of compensatory adaptation may significantly decrease the brain’s available resources for processing sound and can affect a deaf patient’s ability to effectively perceive speech with their cochlear implants,” Sharma said.
Sharma and her students have also discovered that this cross-modal reorganization occurs not only in patients with profound deafness, but also in those with only a mild degree of hearing loss. And as the hearing areas of the brain shrink, other centers of the brain, such as those normally used for higher-level decision making, are activated just by listening and trying to process sounds. According to Sharma, these changes increase the overall load on the brains of older adults, and may help to explain the research that shows age-related hearing loss is a factor in dementia.
The implications of the study
The team’s findings point to the need for early screening programs for hearing loss in adults. And they further illustrate the fact that age-related hearing loss needs to be taken more seriously, even when it is still mild. Hearing loss is older adults very prevalent and often seen as a harmless side-effect of aging, but as this recent research has revealed, the reorganization of the brain that can occur even with mild hearing loss could have serious consequences for the aging brain.
“One in three adults over the age of 60 has age-related hearing loss,” Sharma said. “Given that even small degrees of hearing loss can cause secondary changes in the brain, hearing screenings for adults and intervention in the form of hearing aids should be considered much earlier to protect against reorganization of the brain.”
Sharma’s group hopes to develop more user-friendly EEG technologies, as they are extremely useful in charting brain changes in patients with hearing loss. When clinicians are able to get an “image” of how hearing loss is affecting the brain, they can use that blueprint as a guide in clinical intervention, Sharma believes.
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