People suffering from a specific type of hearing loss might also be more prone to memory loss, a new study concludes.

Image credits: mike krzeszak / Flickr.

Hearing loss can have many causes. Instant or temporary loss can be caused by earwax, infections, injuries or other diseases, but the more common hearing loss is chronic. Gradual hearing degradation is usually caused by aging or repeated exposure to loud noises. Hearing loss is one of the most common disabilities for the elderly, with one in three people 65 and over suffering from it. Now, a new study raises even more concerns about this health issue, as researchers conclude that a certain type of hearing loss is associated with mild cognitive impairment.

Researchers recruited 1,604 participants from the Great Age Study, a population-based study conducted in the south of Italy, with an average age of 75, testing their hearing and cognitive skills. Out of the participants, 26 percent had some peripheral hearing loss and 12 percent had central hearing loss, while 33 percent were diagnosed with mild cognitive impairment. Peripheral hearing loss is typically associated with a degradation of the inner and hearing nerves, while central hearing loss is caused by problems in the brain’s ability to process sound.

People suffering from central hearing loss would say things like “I can hear you talking but I can’t understand.” For this reason, some classify it as a learning disability rather than a hearing loss. However, it is nevertheless a deficit located on the neural pattern of the auditory functions, and can therefore be regarded as a hearing disorder.

Researchers found a significant correlation between central hearing loss and cognitive impairment. Out of the 192 people with central hearing loss, 144 of them — 75%, compared to 60% for people with no hearing loss — had mild cognitive impairment. However, the correlation didn’t carry over to people suffering from peripheral hearing impairment, who weren’t more likely to suffer from any cognitive degradation than people without any hearing loss.

“These preliminary results suggest that central hearing loss may share the same progressive loss of functioning in brain cells that occurs in cognitive decline, rather than the sensory deprivation that happens with peripheral hearing loss,” said study author Rodolfo Sardone AuD, EngD, MPh, at the National Institute of Health and University of Bari in Italy. “It’s a problem with perception. Tests of hearing perception should be given to people who are older than 65 and also to people with cognitive impairment.”

However, this study only established a correlation and didn’t seek to explain any causation. In other words, we don’t know if one is causing the other, or if they are unrelated. Still, Sardone has an idea about the mechanism behind this process. In an email to ZME Science, he wrote:

“Sensory deprivation leads to a weakening of the neural structures of the brainstem and the temporal cortex, very similar to the well-known neuroscientific concept of “use it or lose it.” A peripheral hearing loss increases the effort and therefore the cognitive load, specifically on the executive functions and working memory, precociously damaged in the degenerative processes like AD. This hypothesis does not explain why in about 9% subjects have speech abnormalities with a normal audiometric threshold.”

In the future, the team will try to find associations between central auditory processing disorder and mild memory impairment to back up their findings.

“The difference between our study and the others is that we’re trying to define the association in the very early stage of cognitive decline like mild memory impairment, and next step will be to explore with longitudinal observations the associations between CAPD and the subjective memory complaint,” Sardone told us.

The study hasn’t been yet peer-reviewed and will be presented at the American Academy of Neurology’s 70th Annual Meeting in Los Angeles.

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