What exactly is hearing loss?

Hearing is one of the senses we use to perceive our environment. There are 5 senses: sight, hearing, taste, smell, and touch. Hearing allows us to pick up sounds from our surroundings, such as voices, music, or sounds that warn us of potential dangers. Our ears pick up this sound information and send it to our brain, where these signals are processed into a meaningful interpretation of the environment. If something goes wrong in this chain, it can lead to hearing loss.

Hearing loss does not mean you can no longer hear anything at all. It means you hear less well than other people. This often shows up as an inability to hear certain pitches or sound levels. It can range from missing some information (mild hearing loss) to hearing almost nothing at all (severe hearing loss). Common causes of hearing loss include:

• Ageing
• Prolonged exposure to loud sounds, such as music or the noise of machinery
• Ear infections
• Congenital conditions

Hearing loss can seriously affect a person's quality of life. For example, it becomes harder to follow conversations, which can lead to a feeling of social exclusion. Listening intensively for long periods is exhausting and requires a lot of energy and concentration, which can lead to mental fatigue. Hearing aids can help prevent these problems. If that is no longer sufficient, sign language may be an option.

How does hearing loss affect the brain?

Sounds are essentially invisible waves of compressed air, vibrations (much like ripples on the surface of water). These vibrations enter your ears through the outer ear, which catches the sound and channels the vibrations towards your eardrum. Inside the ear, 3 small bones vibrate along with the eardrum and pass these vibrations on to the inner ear (cochlea).

There, the vibrations are converted into electrical signals (the language of the nervous system). The auditory nerve carries these electrical signals to the brain, to an area called the primary auditory cortex. This area sits on both sides of your head, at the level of your temples and just in front of your ears (temporal lobe). Interestingly, this area lies close to the hippocampus, a brain region involved in memory that gradually deteriorates in people with dementia.

The primary auditory cortex is the first stop where auditory information enters the brain and where sound is detected. After that, more brain areas are involved in understanding and giving meaning to sounds (auditory association cortex) and combining information from other senses (multisensory association cortex). All of this happens incredibly fast, as we have been exceptionally good at picking up and responding to sounds since prehistoric times. That ability was essential for protecting ourselves from potential dangers.

When hearing loss occurs, something goes wrong somewhere in this chain. Sometimes the problem starts in the inner ear, due to damage to the eardrum or the cochlea (for example from prolonged exposure to loud sound). But sometimes the problems are further up the chain, and the auditory cortex has become less effective at processing auditory signals.

Possible mechanisms explaining the link between hearing loss and dementia risk

For a long time, there was not enough reliable evidence that untreated hearing loss could be a risk factor for dementia. In recent years, however, a number of larger studies have provided more evidence. The article published in The Lancet analysed these studies and summarised the findings.

The conclusion was that people with hearing loss have a significantly higher risk of developing dementia than people with normal hearing. But this risk can be reduced by addressing hearing loss, for example by using a hearing aid. The researchers also concluded that making hearing aids available worldwide to those who need them could be cost-effective in the long run.

The cause-and-effect relationship between dementia and hearing loss is less well understood, and the evidence for whether hearing loss causes dementia or vice versa is limited. This relationship is likely quite complex (see also: ACHIEVE study).

Less social activity

Several theories exist about how untreated hearing loss and dementia are connected. One is that people with hearing loss may become less socially active. We have long known that sufficient social contact, which also keeps the brain active, is important for healthy cognitive ageing, and that a lack of social connections increases the risk of dementia.

Mental energy

Hearing loss may contribute to dementia because the brain is constantly working hard to understand sounds and speech. This requires a great deal of mental energy. Over time, this increased demand on concentration may exhaust the brain and speed up cognitive decline.

Fewer auditory signals

Another theory is that when the auditory cortex receives fewer sound signals, the connections between nerve cells in that area weaken, making information transfer less effective. The brain works on the principle of "use it or lose it". New auditory signals are needed to keep the information chain functioning well. This brain area can literally shrink as a result.

Hearing loss caused by dementia

Dementia itself may also cause hearing loss, because dementia affects the brain areas that process sound, making hearing more difficult. Researchers have not yet reached agreement on what is cause and what is effect. More studies will follow in the future to shed light on the relationship between the two.

What can you do in the meantime?

Protect your ears with hearing protection against (prolonged) exposure to loud sounds. If you already have some hearing loss, considering a hearing aid is a sensible step. Make sure the hearing aid is properly fitted. Visit your GP and/or hearing specialist for advice and to have your hearing aid correctly adjusted (read more: Alzheimer's Association | Hearing loss and dementia).

Alongside protecting your hearing, it is also important to keep the brain active with a variety of sensory stimuli. Bike Labyrinth can help with that. Bike Labyrinth uses both auditory and visual stimuli. There are also audio routes where points of interest along the route are narrated. On screen, text and information about these highlights can be read as well. Experience the routes together for social stimulation and make it a truly multisensory experience.