Over the past decade, a growing body of evidence has revealed that hearing loss is strongly associated with decreased functional brain tissue volume and cognitive decline. That leads many people to the question, can hearing loss shrink your brain?
Firstly, no research to date shows that hearing loss leads to brain shrinkage and cognitive decline. In other words, cognitive impairment, including dementia and brain atrophy, is not demonstrably caused by hearing loss.
The human brain is a remarkable and highly complex organ. Researchers don’t yet understand if hearing loss leads to cognitive impairment and structural brain changes directly or indirectly.
However, there is a significant correlation between hearing loss and cognitive impairment, and therefore unmanaged hearing loss may accelerate brain shrinkage.
Why is Brain Shrinkage Implicated in Hearing Loss?
Brain shrinkage or cerebral atrophy refers to a decline in brain cells, called neurons, or a loss of connections between neurons. Brain atrophy may be limited to one area of your brain or affect the whole brain.
According to the National Institute of Neurological Disorders and Stroke (USA), cerebral atrophy is caused by normal aging, various diseases and disorders, infections and brain injuries. Included in the list of causes are Alzheimer’s disease and other forms of dementia.
In an analysis published in Laryngoscope Investigative Otolaryngology, researchers summarised the results of 17 reliable studies. They found age-related hearing loss is associated with an increased risk of dementia, cognitive decline and cerebral atrophy.
With almost ten years of studies indicating a link between hearing loss and dementia, brain shrinkage is a significant correlating factor of these two disorders.
What Is Alzheimer’s and Dementia?
Although often used interchangeably, Alzheimer’s and dementia are not the same things. Dementia is not a single disease; it’s a general term like heart disease. It covers a broad spectrum of distinct medical conditions, including Alzheimer’s disease. The Alzheimer’s Association (USA) estimates Alzheimer’s disease accounts for 60-80% of cases of dementia.
Dementia is a progressive cognitive decline that impedes a person’s ability to live life independently. Dementia can impair:
- awareness of surroundings
- learning ability
- visual-spatial judgment
- higher executive functions such as:
- mental flexibility
- abstract thinking
This impairment of mental faculty is bad enough to interfere with social and work skills.
The Alzheimer’s Society (UK) explains modern brain scan studies have found that an increased rate of brain shrinkage can reliably and predictably diagnose future cognitive decline in patients. The most common types of dementia each start with shrinkage of brain tissue.
How Does Hearing Loss Cause Brain Shrinkage?
Hearing loss doesn’t cause brain shrinkage. However, numerous studies have revealed a relationship between age-related hearing loss and structural brain changes exists.
Hearing loss is a type of sensory deprivation known as auditory deprivation. Depriving the brain of sound for an extended period, such as with untreated hearing loss, weakens the auditory cortex, making hearing more difficult.
Brain scans have shown the brain frequently has to work extra hard to compensate for hearing loss. This extra effort or cognitive load over taxes the brain, altering “normal” brain activity patterns. When this happens, areas of the brain dedicated to higher-level thinking are “borrowed” for processing sound—leaving them unavailable to do their original function.
With increasing listening effort, structural brain changes occur, and cognitive decline and brain atrophy may set in much quicker than if the brain could process sounds normally. A compensatory brain reorganisation could explain why age-related hearing loss is strongly correlated with brain atrophy and dementia.
Demonstrating a Link Between Hearing Loss and Brain Atrophy
A 2011 study published in the Journal of Neuroscience demonstrated a significant linear relationship between hearing ability and brain tissue (gray matter) volume in the primary auditory cortex (the first relay station for auditory information in the brain).
The author’s also state they think it’s “…plausible that changes in older adults’ peripheral hearing ability had a causal role in reducing gray matter volume in the auditory cortex.”
A 2014 study published in NeuroImage found that individuals with hearing impairment had more accelerated brain shrinkage in the right temporal lobe than participants with normal hearing.
Hearing Impairment Is Associated with Smaller Brain Volume in Aging published in Frontiers in Aging Neuroscience in 2016 studied the relationship between hearing impairment and brain volume in 2,908 participants with an average age of 65 years. The researchers found that people with worse hearing were significantly associated with a smaller brain volume.
Anu Sharma, PhD, a researcher in the Department of Speech-Language and Hearing Science at the University of Colorado, studied how hearing loss alters the brain’s physical structure.
Sharma and her colleagues have shown when areas of the brain responsible for hearing receive degraded or decreased input due to hearing loss, parts of the brain that normally process sound may be “repurposed” by other intact and active brain functions.
“The hearing areas of the brain shrink in age-related hearing loss,” said Sharma. “Centers of the brain that are typically used for higher-level decision-making are then activated in just hearing sounds. These compensatory changes increase the overall load on the brains of aging adults. Compensatory brain reorganisation secondary to hearing loss may also be a factor in explaining recent reports in the literature that show age-related hearing loss is significantly correlated with dementia.”
What Can You Do To Help Prevent Hearing Loss and Brain Shrinkage?
Interestingly, studies have shown changes in brain structure may occur as soon as three months after the onset of hearing loss and could be reversible by a well-fitted hearing aid.
Simple interventions for conductive hearing loss, such as earwax removal, can also be highly effective.
If the association between hearing loss and cognitive decline is causal, it follows that rehabilitation for hearing loss can positively impact cognitive decline.
Hearing loss should not be dismissed as a normal part of aging and instead treated for structural changes in the brain.
What Can We Do to Help Prevent Dementia Cognitive Decline?
According to Dementia prevention, intervention, and care: 2020 report of the Lancet Commission, modifying 12 risk factors might prevent or delay up to 40% of dementias. Modifiable risk factors include:
- Education in early life
- Hearing loss
- Traumatic brain injury
- Alcohol misuse
- Later life:
- physical inactivity
- social isolation
- air pollution
The report recommends staying cognitively, physically, and socially active in midlife and later life. Regular exercise protects from dementia, perhaps by lowering obesity, diabetes, and cardiovascular risk. Using hearing aids is also explicitly mentioned to reduce the risk posed by hearing loss.