Age-related hearing loss (or presbyacusis) highlights a causal link between one’s age and the rate of hair cell degradation in the cochlea of the inner ear. Recent research has also linked cognitive decline and unmanaged hearing loss, to the progression of dementias such as Alzheimer’s disease. This article investigates the issue in a little more depth and recommends just how the two might be linked.
How We Hear?
The process of ‘hearing’ may be described as a series of mechanical processes which ensure the efficient transfer of sound through the air filled outer and middle ear chambers to the fluid filled inner ear. On a very basic level the outer ear captures and funnels sound vibration, the eardrum correspondingly vibrates which in turn enables the effective transfer of acoustic energy across the ossicular chain, located in the middle ear. The cochlea, located in the inner ear, is responsible for receiving sound vibration and converting it into a nerve impulse which is then transferred via the auditory nerve to the brain for re-interpretation. The receptors which enable this final process are thousands of tiny hair cells, or stereocilia.
It is a logical consequence that any impediment to the transmission of sound, whether the outer, the middle or the inner ear will have an impact on one’s auditory capability. Whilst conductive losses (affecting the outer or middle ear) do occur, the most prolific cause is attributed to hair cell decline in the inner ear. As the body ages the hair cells diminish in both quantity and quality; the inability of the body to replicate or regenerate replacement cells means that the resultant hearing loss is in consequence, permanent. The rate of hair cell decline varies for people within the same social generation, this may be due, in part to other extraneous factors such as hereditary links, degrees of noise exposure or even use of certain ototoxic medication -notwithstanding this however it is a widely accepted reality that by the age of 70, three in every four people are affected. Without management, this type of sensory (and oftentimes age-related) impairment is increasingly being cited as a possible catalyst for the progression of dementia.
Hearing Loss and Cognitive Decline
Age related hearing loss rarely leads to subtotal hearing loss. For most individuals the volume of sound is maintained but the level of intelligibility, or clarity, is compromised. For many, this manifests in the perception that people mumble or speak indistinctly. In cases where intervention is not sought it is quite common to see parity between social isolation and cognitive decline. The resources used both physically and psychologically in trying to understand the pace and tenet of speech must not be underestimated. Coupled with the potential for mis-interpretation, the fear of being mocked and general discomfiture, it is little wonder that avoidance is often easier than
It is the symbiosis between reduced auditory stimulus and patterns of reclusiveness which are causing concern. Recent studies, such as that published in the Journal of the American Medical Association, do not provide a definitive account as to the precise cause of dementia but certainly highlight that untreated hearing loss is an important and incontrovertible factor in the acceleration of these conditions.
Studies by the Johns Hopkins University, have also determined that socially isolated individuals are more likely to develop dementia. Out of 639 participants, researchers found that those with hearing loss at the beginning of the study were significantly more likely to develop dementia by the end. In fact, the risk of developing dementia over time was believed to increase by as much as fivefold.
Managing Hearing Loss
It is of primary importance that any hearing deficit, whether raised by the individual, family member or caregiver, is fully investigated by a health professional. An initial consultation will rule out temporary causes, such as ear wax blockage, establish the general health and condition of the outer ear and assess the hearing threshold level against a normative value. The hearing test, which is normally conducted at a private hearing center, is vital in determining the correct means of intervention. Depending upon the extent of one’s loss and individual lifestyle requirements, remediation may be accessed through hearing aid amplification, use of situation-specific devices, such as amplified telephones or basic lifestyle changes. Whilst there is no cure for hearing loss it is about finding ways of managing the condition and enabling effective communication. Techniques such as facing the speaker, being aware of the room acoustics and limiting background noise can all help, whether used alone or in conjunction with amplification devices.
Written by Melanie Lewis who is a trained hearing aid audiologist at www.HearingDirect.com
The Johns Hopkins University – http://www.hopkinsmedicine.org/news/media/releases/hearing_loss_and_dementia_linked_in_study
Harvard University. – http://www.health.harvard.edu/blog/hearing-loss-may-be-linked-to-mental-decline-201301225824