Hearing loss and its effect on cognitive function

Often in our everyday clinical work, we hear adult patients saying their hearing loss is “normal” for their age. It is important to understand that while having hearing loss is not unusual, its presence affects an individual’s wellbeing significantly more than what meets the “ear”. In other words, implications of hearing loss extend well beyond its effect on individual’s communication and listening abilities.

A growing body of research establishes hearing loss to have a co-morbidity and relation with several chronic health conditions such as diabetes, mental health, cardiovascular disease and more. Hearing loss is also one of the most significant factors which impacts cognitive function. This blog aims to present a better understanding of this relationship between hearing loss and cognition and why it is important to keep our hearing function in check. Let’s dive in a little bit more!

What is hearing and cognition?

Hearing is one of the five senses through which we connect with the world around us. While all senses help in cognizing information, it is through hearing that we engage in meaningful communication and connect with fellow living beings. Hearing loss in a technical sense is an elevation of hearing thresholds above the normal hearing range measured across a frequency range typically from 250 Hz to 8000 Hz.

For adults, a hearing threshold above 20 dB (decibel) is considered as hearing loss and can vary in degree from mild to profound. Hearing loss is also defined on its origin in the ear- hearing loss can occur due to an impediment to conduction of sound energy reaching inner ear (the organ of hearing aka cochlea), an issue with inner ear itself or a combination of both. Hearing loss as a condition in a broad sense is generally associated with changes at the peripheral hearing organ level or simply put, at the ear level.

Cognition, on the other hand, is a higher-level function of the brain and involve mental processes which allow us in comprehension, thinking, remembering, judging, problem solving. It is also associated with imagination, planning and reasoning.

So how does hearing loss at the ear level affects higher level cognitive function?

A review by Wayne and Johnsrude in 2015 to understand a causal relationship have suggested possible mechanisms such as a decline in sensory faculty causing increase in cognitive efforts and information degradation due to hearing loss leading to impoverished perceptual input contributing towards cognitive decline. Another group of researchers have suggested that chronic hearing loss impacts at a neural level with reduced activation in central auditory pathways, resulting in more compensation from cognitive control network and therefore reducing cognitive reserve and thus affecting executive functions of the brain (Rutherford et al., 2018).

Hearing loss has been identified as biggest modifiable mid-life factor in cognitive decline (Lancet Commission Report, Livingston G. et al, 2020).  It is worth mentioning that late-life factors affecting cognitive function include social isolation and depression which are also related to someone experiencing significant hearing loss. Studies have shown that risk of dementia doubles with even mild hearing loss, triples with moderate hearing loss and increases to 5 times for someone with severe hearing loss (Liu and Lee, 2019).  

While there is ample evidence to support just how important our hearing health is towards our cognitive wellbeing, on average individuals with hearing loss wait for 7 years before seeking help. One of the reasons why hearing is one of more ignored health modalities is that generally hearing loss progression is gradual and in early stages can be perceived as an issue with speaker’s way of talking rather than a decrement of own’s hearing. Because the change is slow, the individual may also learn to compensate for missing information through contextual and visual cues without realising that the auditory function is being compromised.

Understanding the insidious effects of hearing loss, even in early stages, it becomes important that hearing function be checked with similar relevance as other health checks. If hearing loss is identified in early stages, it should be monitored annually to keep track on any progression. If the hearing loss detected is of significant extent and permanent or if hearing loss is affecting day-to-day communication, measures should be considered to address its impact. One of the most important interventions for permanent hearing loss is use of hearing aid.

Do hearing aids slow the progression of cognitive decline?

The use of hearing aids has been found to enhance working memory performance and increased cortical response amplitudes. (Karawani et al., 2018). A large study conducted in the UK found that hearing aid use was associated with better cognition independent of social isolation and depression (Dawes et al., 2015). As hearing aids enable an individual to engage in more effortless communication, it reduces social isolation imposed due to hearing loss and therefore plays an important role in enhancing quality of life measures.

In conclusion, although hearing loss may be viewed as a peripheral condition limited to its effects on an individual’s ability to hear speech, there is evidence indicating that it has a significant bearing on several health domains including cognitive function. It is established to be the most significant factor affecting cognitive health in mid-life which is modifiable. Monitoring, early detection and intervention of hearing loss is the key towards preventing its deleterious effects on cognitive health and general wellbeing.

This blog was written by Dr. Manuj Agarwal (Au.D), Principal Audiologist at Vital Hearing and Balance clinic providing high quality hearing services and operates in Ashburton, Dandenong, and Belgrave regions in Melbourne.

References:

1. Wayne R. V., Johnsrude I. S. (2015). A review of causal mechanisms underlying the link between age-related hearing loss and cognitive decline. Ageing Res. Rev. 23 154–166.

• Rutherford BR, Brewster K, Golub JS, Kim AH and Roose SP (2018) Sensation and psychiatry: linking age-related hearing loss to late-life depression and cognitive decline. American Journal of Psychiatry 175, 215–224.

•  Dementia prevention, intervention, and care: 2020 report of the Lancet Commission.

• Liu CM, Lee CT. (2019) Association of hearing loss with dementia. JAMA

• Dawes P, Emsley R, Cruickshanks KJ, Moore DR, Fortnum H, Edmondson-Jones M, McCormack A and Munro KJ (2015) Hearing loss and cognition: the role of hearing aids, social isolation and depression.

• Karawani H, Jenkins K and Anderson S (2018) Restoration of sensory input may improve cognitive and neural function. Neuropsychologia 114, 203–213.