Presbycusis

One Person’s Lifelong Experience with Hearing Loss

By Dr. Bruce L. Douglas

I am a 93-year-old healthy adult with hearing loss. Many parts of my body don’t work perfectly right anymore, but my hearing loss is my biggest physical difficulty.

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When it comes to hearing loss, I’ve been there and done that. Despite the fact that I am legally deaf, I can hear. Why? Because I’ve stubbornly fought back every time a hearing pitfall appeared in my path.

The reason I can hear is because I refuse to give into my disability. I try out every kind of useful assistive hearing device I can lay my hands on or is given to me by my Department of Veterans Affairs (VA) audiologist. I’ve become a hearing loss activist and fight for coiling of public facilities whenever I have the chance to do so. And I recently had a cochlear implant installed about a year ago.

As a boy, I remember always taking a seat at the front of the room, when most other kids would vie for one in the back, so they could cheat on exams without being seen by the teacher. I didn’t realize how poor my hearing was until I was reprimanded for inconspicuously (I thought) using a nail clipper under my desk in my elementary school classroom. I had no idea because I couldn’t hear it!

I tried to come to terms with my hearing loss for many years. I refused to hide in corners of rooms and restaurants, and dealt with my problem largely by disclosing my hearing loss to people and asking for their cooperation in our verbal relationships. My early hearing aids only allowed me to hear sounds but not comprehend them, so I learned to lip read and stare at my companions, often to the point of distraction.  

I have presbycusis, I’m suffering from acoustic trauma from my time in the Korean War, I have sensorineural deprivation, and I’ve experienced every imaginable kind of sound and sensation in the form of tinnitus.

Call us what you will, but don’t ignore us; don’t make fun of us. Most importantly, respect us; and treat us as equals. Be patient with us and accept the reality that we have an invisible condition that wove its way into our nervous system, most often beyond our control, and we do all we can to listen to you and respond to the best of our ability.

Dr. Bruce Douglas is a Professor of Health and Aging at the University of Illinois at Chicago School of Public Health. He is a participant in HHF’s Faces of Hearing Loss campaign.

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Presbycusis and the Deterioration of Neural Nets

By Khaleel A. Razak, Ph.D.

This shows cells of the auditory cortex from a young mouse. Cells can be parvalbumin positive (red), or perineuronal positive (green), or have both parvalbumin and perineuronal nets (red surrounded by green). In our paper we show that all three cell types decline with presbycusis. These changes can cause functional deficit in auditory processing.

This shows cells of the auditory cortex from a young mouse. Cells can be parvalbumin positive (red), or perineuronal positive (green), or have both parvalbumin and perineuronal nets (red surrounded by green). In our paper we show that all three cell types decline with presbycusis. These changes can cause functional deficit in auditory processing.

Age-related hearing loss, or presbycusis, affects a third of the population ages 65 and older, and nearly half the population older than age 75. As a result, it is one of the most prevalent hearing disorders, and it also has a high potential for associated tinnitus and deficits in speech recognition.

Presbycusis leads to myriad changes in the central auditory nervous system. One consistent change is the decline in the ability of auditory system neurons to transmit and receive information with precise timing. The timing precision is somewhat like time-stamping a sound, helping to locate and decode it.

As a result, because of changes to the both the inner ear as well as to the central brain regions that process sound, a combination of hearing aids, behavioral training, and pharmacological treatments will be necessary to alleviate presbycusis-related processing deficits. A key step in developing such a combination method is to understand the mechanisms underlying the changes in neurotransmission in the auditory system and to determine how these changes affect sound processing.

Our paper “Age-Related Deterioration of Perineuronal Nets in the Primary Auditory Cortex of Mice,” which was published in the journal Frontiers in Aging Neuroscience, focuses on a specialized structure in sensory cortex known as perineuronal nets (PNNs). Made up of large molecules, PNNs are like a mesh helping to stabilize synapse function among neurons. These extracellular matrix components preferentially surround inhibitory neurons in the auditory cortex and are known to be critical to the function and survival of the neurons they surround.

Specifically, a group of neurons known as parvalbumin-expressing (PV+) neurons are surrounded by PNNs. PV+ neurons play a role in network synchronization and providing inhibition that shapes precise temporal encoding. Reduction in the function of PV+ neurons can lead to the processing deficits observed in presbycusis.

Using two different mouse models, we show that PNN expression is reduced with age, and that an age-related decline in PNNs with presbycusis may be related to changes in synapse function, affecting the processing of sound, particularly those that require proper timing. Because PNNs can be pharmacologically regulated, future studies will test if deterioration of PNNs with presbycusis can be delayed or prevented.

Khaleel A. Razak was a 2009 and 2010 Hearing Health Foundation Emerging Research Grants recipient. This study was started with funding by the Hearing Health Foundation in 2009-2010.

We need your help supporting innovative hearing and balance science through our Emerging Research Grants program. Please make a contribution today.

 
 
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New Insights Into Age-Related Hearing Loss

By Ruili Xie, Ph.D.

Age-related hearing loss (ARHL), also known as presbycusis, is one of the most prevalent health conditions affecting older adults. The leading cause of ARHL is generally attributed to damage in the ear during aging, which include the loss of the inner ear’s sensory hair cells and spiral ganglion cells (SGCs).  

Hair cells act like antennae for the auditory system to receive sound information from the environment. SGCs are the nerve cells that connect the ear and the brain, with their peripheral branches receiving sound information from hair cells, and their central branches forming the auditory nerve to pass information to the brain. Recent studies showed that the terminals (endpoints) of SGC peripheral branches are vulnerable and can be damaged during aging, which are thought to be the primary cause of ARHL.    

However, the majority (over 70 percent) of SGC peripheral terminals survive normal aging. It is unclear whether, with age, sound information is reliably transmitted through the surviving SGCs to the brain; and if not, how this may contribute to ARHL.

One particular point of interest lies in the terminals of the SGC central branches (the auditory nerve synapses) that activate their target neurons in the brain. Deterioration in the information flow at these synapses with age would reduce sensory input to the brain and lead to ARHL.

For the first time, Dr. Paul B. Manis and I have found that the transmission of information from SGCs to their target neurons in the cochlear nucleus (the first auditory station in the brain) is compromised in aged mice with ARHL. The transmission process deteriorates due to abnormal calcium signaling at the central terminals of the SGCs. The study not only proposes a novel brain mechanism that underlies ARHL, but also provides new strategies in developing future clinical treatments.

 

Ruili Xie, Ph.D., a 2009 and 2010 Emerging Research Grants recipient, is an assistant professor in the Department of Neuroscience at the University of Toledo, in Ohio.The study “Synaptic Transmission at the Endbulb of Held Deteriorates During Age-Related Hearing Loss” appeared in The Journal of Physiology on Sept. 13, 2016.

We need your help supporting innovative hearing and balance science through our Emerging Research Grants program. Please make a contribution today.

 
 
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