The Connection Between Hearing Loss and Dementia

By Alycia Gordan

June is Alzheimer's & Brain Awareness Month and Hearing Health Foundation would like to shine light on the effects untreated hearing loss can have on our brains and memory. Hearing loss is often linked with dementia, and research is being conducted to establish the exact link between the two. Evidence suggests that by treating hearing loss, the risk of dementia can be mitigated.

Dementia is a medical term that is used to describe a host of symptoms, characterized by a deterioration in a patient’s cognitive abilities. The degeneration of brain cells causes neurons to stop functioning, leading to a series of dysfunctions.

A person may have dementia if at least two of his mental faculties are affected: the loss of memory and focus; difficulty communicating; short or interrupted attention spans; impaired judgment; or an inability to perform everyday tasks.

Frank Lin, M.D., Ph.D., an associate professor of otolaryngology and epidemiology at Johns Hopkins University, conducted a study in 2011 in which the mental abilities of 639 cognitively stable individuals were supervised regularly for 12 to 18 years. The results indicated that volunteers with normal hearing were much less susceptible to acquiring dementia while those with mild, moderate, and severe hearing loss were two, three, and five times more susceptible to the disorder, respectively.

Another study conducted by Lin in 2013 involved observing the cognitive abilities of 1,984 older adults over six years. The research concluded that older adults with hearing loss tended to experience 30 to 40 percent accelerated cognitive dysfunction and were at a higher risk of developing dementia.

What Is the Cause?

Since the exact link between hearing loss and dementia is still a mystery, there are theories about how the former may aggravate the latter.

One of the theories suggests that if the brain struggles to cope with degraded sounds, its resources are allocated to processing these sounds and this “cognitive load” causes a decrease in overall cognitive functioning. Moreover, hearing loss accelerates atrophy in the cerebrum which is not exclusive to processing sound as it also plays a role in memory. In addition, it is speculated that social isolation that results from hearing loss causes stress and depression and exacerbates cognitive deterioration.

What Is the Solution?

Not many studies have been conducted to check the influence of treating hearing loss for treating dementia. However, the studies that have been conducted so far do provide considerable hope.

One way to improve profound hearing loss is receiving cochlear implants. French researcher Isabelle Mosnier, M.D., of the Assistance Publique-Hôpitaux de Paris, evaluated the effect of cochlear implants on cognitive functioning in 94 elderly people who had profound deafness (in at least one ear).

Mosnier found that hearing rehabilitation improved not only cognitive functioning of the elderly, but their speech perception as well.

The most direct link between auditory impairment and memory loss is the brain. Thus, any stimulus that helps the brain remain alert will keep the person active too. Hence, researchers are considering the use of music therapy to restore cognitive functions in people who suffer from memory loss.           

Concetta Tomaino, a cofounder of the Institute for Music and Neurological Function, found that music stimulates parts of the brain made inactive by dementia. In a pilot study, music therapy sessions were conducted with 45 individuals with chronic dementia and the results showed that neurological and cognitive abilities improved significantly for those in the music group.

This research shows there are techniques that can aid individuals with dementia and hearing loss. If you or a loved one has hearing problems, please see a hearing health professional to get a hearing test in order to potentially prevent future cognitive issues. 

Alycia Gordan writes for Brain Blog.

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Second Cause of Hidden Hearing Loss Identified

By Michigan Medicine - University of Michigan

Some people can pass a hearing test but have trouble understanding speech in a noisy environment. New research identifies a new mechanism for this condition just years after its discovery. Credit: Michigan Medicine

Patients who complain they can't hear their friends at a noisy restaurant, but pass a hearing test in their doctor's office, may be describing hidden hearing loss.

Now, less than six years since its initial description, scientists have made great strides in understanding what hidden hearing loss is and what causes it. In research published in Nature Communications, University of Michigan researchers report a new unexpected cause for this auditory neuropathy, a step toward the eventual work to identify treatments.

"If people can have hidden hearing loss for different reasons, having the ability to make the right diagnosis of the pathogenesis will be critical," says author Gabriel Corfas, Ph.D., director of the Kresge Hearing Research Institute at Michigan Medicine's Department of Otolaryngology -- Head and Neck Surgery.

Corfas published the research with co-author Guoqiang Wan, now with Nanjing University in China. They discovered using mice that disruption in the Schwann cells that make myelin, which insulates the neuronal axons in the ear, leads to hidden hearing loss. This means hidden hearing loss could be behind auditory deficits seen in acute demyelinating disorders such as Guillain-Barré syndrome, which can be caused by Zika virus.

Corfas and Wan used genetic tools to induce loss of myelin in the auditory nerve of mice, modeling Guillain-Barré. Although the myelin regenerated in a few weeks, the mice developed a permanent hidden hearing loss. Even after the myelin regenerated, damage to a nerve structure called the heminode remained.

Synapse loss versus myelin disruption

When the ear is exposed to loud noises over time, synapses connecting hair cells with the neurons in the inner ear are lost. This loss of synapses has previously been shown as a mechanism leading to hidden hearing loss.

In an audiologist's quiet testing room, only a few synapses are needed to pick up sounds. But in a noisy environment, the ear must activate specific synapses. If they aren't all there, it's difficult for people to make sense of the noise or words around them. That is hidden hearing loss, Corfas says.

"Exposure to noise is increasing in our society, and children are exposing themselves to high levels of noise very early in life," Corfas says. "It's clear that being exposed to high levels of sound might contribute to increases in hidden hearing loss."

The newly identified cause -- deficiency in Schwann cells -- could occur in individuals who have already had noise exposure-driven hidden hearing loss as well. "Both forms of hidden hearing loss, noise exposure and loss of myelin, can occur in the same individual for an additive effect," Corfas says.

Previously, Corfas' group succeeded in regenerating synapses in mice with hidden hearing loss, providing a path to explore for potential treatment.

While continuing this work, Corfas started to investigate other cells in the ear, which led to uncovering the new mechanism.

There are no current treatments for hidden hearing loss. But as understanding of the condition improves, the goal is for the research to lead to the development of drugs to treat it.

"Our findings should influence the way hidden hearing loss is diagnosed and drive the future of clinical trials searching for a treatment," Corfas says. "The first step is to know whether a person's hidden hearing loss is due to synapse loss or myelin/heminode damage."

Materials provided by Michigan Medicine - University of Michigan. Co-author Guoqiang Wan, Ph.D., was a 2014 Emerging Research Grants recipient funded by the Wes Bradley, M.D. Memorial Grant.

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A Healthy Heart Could Mean Better Hearing Health

By Frankie Huang

In honor of American Heart Month in February, Hearing Health Foundation wants to shine light on the link between heart disease and hearing loss. According to the Centers for Disease Control and Prevention, 610,000 Americans die from heart disease each year, making it the leading cause of death for men and women in the U.S.

Heart disease is linked to or causes numerous health issues, including hearing loss. One study suggests that low-frequency hearing loss may be able to predict cardiovascular health. Using an audiogram, researchers were able to determine the probability of cardiovascular disease in men and women. The study found that there was a correlation of heart attacks in men, and a correlation of claudication (pain caused by too little blood flow) in women.

High blood pressure can also be a contributing factor to developing hearing loss, since the inner ear is sensitive to blood flow. High blood pressure damages blood vessels and increases the risk of plaque buildup in the arteries, making it harder for blood to flow throughout the body. In other words, inadequate blood flow and nerve damage in the inner ear may lead to irreversible hearing loss.

A common cause of heart disease and hearing loss is smoking. Smoking increases blood pressure and plaque buildup, and causes hardening of the arteries, all of which decreases blood flow to the organs and other parts of the body. The effects of smoking damages the cardiovascular system, boosting the risk of hearing loss. Additionally, cigarettes contains nicotine, disrupting the neurotransmitters in the auditory nerve (which tell the brain which sound you are hearing) and preventing the brain to accurately interpret sound. Cigarette smoke contains many harmful chemicals that are believed to be ototoxic (toxic to the ear) that may damage hair cells.

There are a variety of ways to prevent heart disease and cut your risk for hearing loss. Eating healthy and incorporating moderate exercise into your daily life can drastically improve your health. Include more fish in your diet: Salmon, mackerel, and herring are high in the omega-3 fatty acids that help reduce high blood pressure and prevent plaque buildup, so you can decrease your overall risk of hearing loss.

Remember, a healthy heart leads to better hearing health.

Music-Induced Hearing Loss: What Do College Students Know?

By Frankie Huang

Music-induced hearing loss (MIHL) is a result from listening to music that exceeds 85 decibels for prolonged periods of time. A decibel, or dB, is a unit to measure sound intensity, and 85 dB is roughly equivalent to the sound of heavy city traffic. Our listening devices and preferred listening levels are the leading cause for MIHL. For example, when you’re working out at the gym and you up the volume of your music to 100% to drown out the music the gym is broadcasting, you are putting yourself at risk for permanent hearing loss.

The frequent use of these devices to listen to music and watch videos typically requires the use of headphones, increasing the risk of MIHL. Portnuff, Figor, and Arehart (2011) found that a person should only use their listening devices for no more than 4 hours per day at 70% volume, or 90 minutes per day at 80% volume.

In a recent study, researchers measured college students’ knowledge on the proper use of listening devices and the effects of listening to music at high volumes. It was found that prolonged use of these devices coupled with loud preferred listening levels is higher in males than in females, with males being less aware of safe listening habits and were more likely to exceed the recommended daily limit. The study also found that female students were more conscious of these limits and more knowledgeable about the maximum listening levels per day, compared with their male counterparts. Furthermore, younger students (freshmen) were less aware of safe listening levels compared with older students who were sophomores.

The use of certain headphones can also increase the risk of MIHL. Among college students, in-ear headphones (e.g., earbuds) are more commonly used than over-the-ear, noise-canceling headphones, and in-ear headphones are associated with a higher risk of MIHL. The biggest difference between in-ear and over-the-ear headphone users was the individual’s listening levels: The study found that in-ear headphone users preferred to listen at a higher volume, while over-the-ear headphone users favored a lower volume because the noise-canceling features meant ambient noise was less of an issue.

Headphone users tend to increase the volume if they can’t block out environmental noises. New York City, for example, is usually noisy so individuals are more likely to listen to their music at a higher volume, which is putting individuals at a greater risk of MIHL. There’s also a greater preference for in-ear headphones between males and females. According to the studies, 52.8% of males believed that in-ear headphones delivered better sound than over-the-ear headphones, compared with 46.4% of females.

Overall, the study suggested that individuals should refrain from listening to music and watching videos at the maximum volume for an extensive amount of time. However, if there’s too much background noise, and it's a distraction, the individual should only increase the volume to 80% of the maximum for no more than 90 minutes daily. In addition, education about the risks of hearing loss and how to prevent it is important, including how noise-canceling headphones drown out environmental noises so the wearer can enjoy music on their personal devices at safer levels.

Hearing loss is irreversible, so investing in a quality headphone that can reduce the risk of MIHL is priceless.

References

Berg, Abbey L. et al. Music-Induced Hearing Loss:What Do College Students Know?. 43rd ed. 2016. Web. 12 Dec. 2016.

http://www.asha.org/uploadedFiles/ASHA/Publications/cicsd/2016F-Music-Induced-Hearing-Loss.pdf

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Summer Is a Time for Play (and Protection)

By Morgan Leppla

“The best offense is one that does not trigger any defense,” says Daniel Gilbert, Ph.D., a psychology professor at Harvard University.

Gilbert says humans are not hardwired to think long term. When people don’t see a threat as immediate, they are not inclined to take action to mitigate it. This psychological phenomenon is why it’s easy to forego protective measures that’ll make a difference in the long run, especially during one of the most fun-filled times of the year: SUMMER!

With its blaring tunes and crackling fireworks, it makes sense that summer excitement distracts us from remembering the permanent effect of noise on our ears. Loud sounds are more insidious than one might expect. This is in spite of the fact that noise-induced hearing loss (NIHL) can happen at any age, to any race, gender, etc. Hearing loss from all causes is a growing epidemic, affecting nearly 50 million Americans.

Sound volume, length of time listening, and repeated exposure to loudness all can lead to NIHL. One extremely loud sound can cause it, but so can exposure to softer (but still dangerous) sounds over an extended period. To put that into tangible terms, a single loud sound may be a shotgun going off right next to you, while sounds that may damage hearing more slowly are repeated exposure to heavy city traffic, music listened to at a high volume using earbuds, or even regular use of a hairdryer!

So, with all of these potential threats to hearing, what is there to do?

Here is the trinity of protection: WALK away from loud sounds, BLOCK loud sounds with ear protection, and TURN the volume down (when you can control it). These simple actions can have a major impact on your long-term hearing health.