Hearing Loss and Cognitive Decline: Understanding the Intersection of Auditory Processing and Brain Health

As a sports specialist chiropractor with a focus on physical and neurological health, I see firsthand the positive impact of maintaining sensory health on overall well-being. Among our senses, hearing plays a role not only in communication but also in maintaining cognitive function and brain health as we age. Emerging evidence suggests associations between hearing loss and an increased risk of developing neurodegenerative conditions such as Alzheimer's disease, Parkinson's disease, and other forms of dementia and cognitive decline. In order to age well, we must be judicious in our attempts to achieve and maintain good health. This includes considering the importance of the structures and mechanisms involved with hearing and the interpretation of sound.

In this week’s newsletter, I want to dive into the fundamentals of the auditory system, touch on the basic pathways associated with auditory processing, and examine how hearing loss may contribute to cognitive decline and other neurological dysfunction over time. By integrating scientific findings, I hope to provide you with some insight regarding how and why it’s important to protect your hearing as you age, and some intuitive yet practical applications we can all implement in our day to day lives.

Understanding the Auditory System: Peripheral and Central Pathways

To understand how hearing loss can influence cognition and brain health, we need to first understand the constituent parts of the auditory system. The auditory system is divided into two anatomically distinct regions: the peripheral and central auditory pathways.

The peripheral auditory system encompasses the outer ear, middle ear, and inner ear structures. These include the ear canal, tympanic membrane (ear drum), ossicles (small bones), and the cochlea. The cochlea is a structure that looks kind of like a seashell and converts mechanical sound vibrations into neural signals that are then transmitted via the auditory nerve. This conversion from mechanical energy to neural signals is thanks to groups of highly specialized cells within the inner ear.

The peripheral auditory system. (Courtesy of: https://www.britannica.com/science/ear/Cochlear-nerve-and-central-auditory-pathways)

The central auditory system begins where the auditory nerve enters the brainstem and extends to brain regions such as the auditory cortex located in the temporal lobe of the brain. Within these central pathways is where sound becomes meaningful to us. There regions are involved in speech recognition, sound localization, and the integration of auditory input with memories, attention, emotion and executive function.

This processing is not just passive. Interpreting what a sound means requires extensive cognitive resources and connections between multiple brain regions. Any dysfunction along these pathways has the potential to impair how sound is processed, even if the peripheral structures remain relatively healthy and intact.

Auditory Processing and Its Connection to Cognitive Networks

Central auditory processing refers to the brain’s ability to decode and interpret auditory inputs, which is highly contextual. When signals encoding sound reach the brainstem, they are relayed to several higher-order centres, including the thalamus, auditory cortex, prefrontal cortex, and hippocampus. This is where the sound is referenced to past experiences, memories and emotions. These regions are not only responsible for interpreting the sound but they also contribute to managing our attention and decision-making relative to the sound we hear. Think about a time that you may have heard something that is reminiscent of a negative moment, emotion or experience. This sound may have left an imprint on you that reflexively activates a stress response, sadness, anger or other emotion. Can you think of an example? Great. Now think about how quickly you actually felt the physical sensation or emotion from the time you heard the sound. It’s pretty fascinating how fast this all happens.

When central auditory function declines, we may struggle to distinguish speech from background noise or fail to localize sounds in our physical surroundings. These difficulties can indicate a broader decline in neural integration. Over time, such deficits may reflect or even contribute to a breakdown in the efficiency of brain regions that are also critical for cognition, emotion, balance, memory and social interaction.

The Evidence Linking Hearing Loss to Cognitive Decline

Over the past decade, mounting evidence has supported the association between hearing loss and increased risk of cognitive impairment. One of the most cited studies, by Lin et al. (2011), followed adults over several years and found a dose-response relationship between hearing loss and dementia. What this means is that the greater and more severe the hearing loss, the greater the likelihood of the onset of dementia. In this particular study, individuals with moderate hearing loss had twice the risk of developing dementia, and those with severe loss faced up to a five-fold increased risk. (!!!)

Further confirmation comes from two meta-analyses, one in 2017 and 2021. Wei et al. analyzed 10 studies and a total of 15,521 subjects and found that hearing impairment is associated with both milder forms of cognitive impairment as well as dementia. In this subject of research, something called the “pure tone threshold” is often used when measuring for hearing impairment. The pure tone threshold is essentially the softest sound intensity that someone with normal hearing can consistently hear at least 50% of the time. The reference value for the pure tone threshold is 0-25 dB. What Lin et al. (2011) found in their study is that for every 10 dB increase above the pure tone threshold that is required to hear (e.g., 10 dB louder for someone to hear what an individual with normal hearing can hear at 25 dB), there is a 20% increase in dementia risk. This dose-response relationship should be all we need to know with respect to doing what we can to protect our hearing as we age.

Lastly and more recently, the ACHIEVE trial conducted by Lin et al. (2023) and published in The Lancet investigated to see if a hearing intervention in those with hearing loss could prevent cognitive decline in those who were cognitively healthy at the time of the trial. The motivation for this trial comes from all the years of previous work establishing that hearing loss is in fact associated with cognitive decline and incident dementia.

Because there are other factors that contribute to cognitive decline, this is can be a very hard thing to study. What the authors concluded is that the adults who were at high risk for cognitive decline (e.g., had other risk factors other than hearing loss) and consistently used hearing aids had a significantly slower rates of cognitive deterioration compared to those who did not use hearing aids. This suggests that interventions targeting hearing loss may offer tangible benefits for brain health, particularly in vulnerable populations.

How Hearing Loss Contributes to Cognitive Decline

The mechanisms behind the association of hearing loss and cognitive decline are multifactorial, involving a blend of cognitive, structural, and psychosocial pathways.

One widely accepted theory is that of increased cognitive load. When hearing is compromised, the brain must work harder to decode auditory signals. This added effort diverts mental resources away from other crucial cognitive operations like memory encoding and decision-making, creating a chronic burden on neural systems. Not only does this produce a physiological burden, but it can often be exhausting for folks who are constantly straining to understand.

Another key mechanism contributing to cognitive demise in those with hearing loss is due to chronic sensory deprivation. As humans, we rely on a constant influx of sensory information about our surroundings and where we are relative to our surroundings in order to navigate in a stable and accurate manner in an ever-changing world. The sound we perceive and the decoding that follows plays a huge role in the health of this process. From localizing sound to determine direction when our vision may be diminished, to contributing to normal vestibular integration, hearing is essential to feel and perform well.

Long-standing hearing loss leads to reduced inputs to the auditory brain regions, which may cause them to atrophy over time. This process may not occur in only one region though. Due a phenomenon called diaschisis nearby and connected areas such as the hippocampus and prefrontal cortex may also undergo neurodegenerative changes due to reduced inputs from the auditory cortex as well as a generalized decreases in social life that comes from hearing loss.

The potential for social isolation that comes from hearing loss also plays a significant role in cognitive decline. Hearing difficulties often lead individuals to withdraw from conversations and social settings due to embarrassment or just because they can’t hear and engage with ease. This reduction in social interaction is a known risk factor for dementia and is associated with both depressive symptoms and reduced cognitive function. Unfortunately, untreated hearing loss can trigger a vicious cycle of deteriorating health that touches our social network and relational health, our physical health, and our neurological health.

Hearing Loss in the Broader Context of Brain Health

As a clinician focused on optimizing musculoskeletal and neurological health, I believe that hearing should be considered just as important as gait and balance, strength, or cardiovascular function. It provides a critical window into the overall status of our brain health and how we process sound. When patients—whether aging adults, children or athletes—report difficulty hearing or following conversations in noisy settings, it may signal broader issues with attention or central processing, not necessarily just problems with the peripheral auditory system.

If you or a loved one is suspecting a hearing deficit, this should be something you chat with your respective healthcare provider about to see if a test is appropriate. Incorporating regular hearing assessments into well-visits may be a proactive step to prevent cognitive decline, particularly in those with other risk factors (see Lin et al. 2023). Collaborating with the appropriate specialists can help identify early signs of decline and tailor interventions accordingly.

Lifestyle Strategies for Protecting Hearing Across the Lifespan

Protecting hearing isn’t just a concern for older adults. In fact, early lifestyle choices play a significant role in preserving auditory and cognitive health across the lifespan. Excessive noise exposure—whether from concerts, industrial workplaces, or headphones—may contribute to earlier onset of hearing loss. Fortunately, there are practical steps we can take to safeguard our auditory systems.

Wearing protective ear-wear in high-noise environments, such as during concerts or when operating machinery can reduce the risk of cochlear damage. Likewise, limiting the duration and volume of headphone use—especially with in-ear devices—may be something to consider.  Luckily, with the new technology on our devices there are sound warnings that prompt us to take a break or turn the volume down, but we have to listen to them for it to be effective. Taking listening breaks, using noise-cancelling headphones to avoid cranking up the volume, and choosing quieter environments when possible all support long-term auditory health.

Lastly, if you already happen to suffer from a known hearing deficit, research suggests that correcting for it using hearing aids significantly reduces the rates of cognitive decline. Read that again. We have the ability to prevent cognitive decline by addressing our hearing. I hope this information empowers those who may be ignoring a hearing deficit to take initiative and seek assessment to help neutralize an otherwise progressive condition and improve your brain's overall health.

Conclusion

There’s no sugar coating it. Research suggests that hearing loss is associated with cognitive decline and incident dementia in a dose-dependent manner. With that in mind (if you’re still with me) we must consider how to preserve our hearing in order to truly optimize our brain health, and subsequently performance, as we age. It really doesn’t have to be much, but it starts with awareness. If you’re aware of this important association, you can then make modifications to your environment to set yourself up for greater success, health and performance. Thanks for reading.

Yours in good health,

Andrew

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