Thanks to Brilliant for  supporting this SciShow video!

To keep building your STEM  skills beyond this video, you can check out Brilliant.org/SciShow. That link will give you 20% off  an annual premium subscription! [♪ INTRO] Getting older is hard.

Not only do your clothes go out of  fashion and slang stops making sense, but you could also lose your hearing  and even experience cognitive decline. And as it turns out, those  two things might be related. The hearing loss and cognitive stuff, that is.

Several studies show that there’s a  link between hearing loss and dementia, though scientists are still working to  understand exactly what’s causing it. While that sounds like it doesn’t bode  well for the majority of elderly people who experience some extent of  hearing loss, this may be good news. Because, while we don’t have  a cure for dementia right now, we do have treatments for hearing  loss, so if hearing loss is a contributor to dementia, we  can do something to prevent it.

Now the term “hearing loss” refers to a  process that happens to people who had average hearing earlier in life, and  experienced a decline in hearing as they aged. This can come from all sorts  of sources, like loud sounds damaging your hearing cells, genetics  making you more susceptible to that sound damage, age-related  brain cell deterioration, and insufficient energy for  hearing cells to function. As it turns out, about two-thirds of adults over 70 years old in the  US experience hearing loss.

And that’s a lot of people! And the extent of their hearing  loss isn’t the same, either. As with most things in life, hearing  falls somewhere on a spectrum.

To get a measurement of the  extent of someone’s hearing loss, they can either fill out a  questionnaire or take a hearing test. The hearing test plays sounds  at different intensities to identify the range of sounds  that the person can hear. If the test results show that they  can’t consistently hear sounds softer than 25 decibels, then  they’re considered to have clinical hearing loss, although  the exact cutoff can vary.

So everyone has a different  cutoff volume where you can no longer consistently hear sounds. It’s called your pure-tone average, or PTA score. The higher your score, the  more severe your hearing loss.

If your PTA score is high enough  for a formal hearing loss diagnosis, then you might have the  option to wear hearing aids to increase the range of sounds you can detect, making hearing aids an effective  treatment for a common problem. The trouble is, only 14% of the people  who need them actually wear hearing aids. Many people never even see a  specialist for hearing loss, thinking that cranking up their TV volume is just another trivial part of getting older,  just like a penchant for hard candies.

But we’re starting to learn  that age-related hearing loss, when untreated, could increase  your risk for developing dementia. A 2011 study from Johns  Hopkins University found that the risk of dementia was increased in  people with age-related hearing loss. Participants with average hearing had lower  risk than those with mild hearing loss, who had lower risk than participants  with moderate hearing loss, who had lower risk than those  with severe hearing loss.

So that would suggest that  the worse your hearing gets, the greater your risk of dementia becomes. And that’s not all. A 2019 study out of Columbia  and George Washington University found that this effect isn’t limited to  the most extreme cases of hearing loss.

The participants in this study that didn’t  meet the clinical threshold for hearing loss still showed cognitive declines compared  to people without any hearing loss. On average, participants with  PTA scores between 1 and 10 scored higher on cognitive tests than  participants with scores of 11 to 20. So even a 10 decibel loss  was significantly associated with cognitive impairment  across a variety of tests.

What’s more surprising is that this  association is even stronger for participants with PTA scores between 1 and 25  compared to those with scores above 25. All this might be a sign that doctors  should reconsider that clinical hearing loss cutoff of 25 decibels so they could detect and treat more subtle hearing loss  that also affects your cognition. That said, we probably can’t go  update all the medical textbooks with a new cutoff until we identify  what a better threshold even would be.

And we still need more data  to say that hearing loss causes dementia in the first place. What we’ve described so far are associations  between hearing loss and dementia, but it’s not clear if the hearing loss is  actually causing the cognitive declines. It could be a link in the chain  that leads to dementia, though.

That 2011 paper pointed out that  people who experience hearing loss have to put more of their  mental resources toward hearing, which may leave fewer resources  for things like memory. On top of that, people experiencing  hearing loss may be socially isolated because communication becomes more difficult. And there’s data linking  social isolation with dementia.

So hearing loss could indirectly lead to dementia by preventing communication  and social interactions. Or hearing loss and dementia  could both be symptoms of some other widespread problem like vascular disease. Which would mean that hearing loss could  be a red flag that dementia is brewing.

And there’s data to back up this red flag idea. The 2011 study showed that people  who developed dementia lost about double the decibels of hearing per year  compared to those who didn’t develop it. But whether or not hearing loss  causes those cognitive declines, the big question is if there’s  anything we can do about it.

If hearing loss is in some way responsible  for people developing dementia, then treating the hearing loss should prevent it, which is where hearing aids come in. But early research into this prevention  technique wasn’t terribly promising, showing no association between  self-reported hearing aid use and dementia. But those researchers didn’t design  their experiment around hearing aids.

The 2011 study didn’t include any  data on how often participants wore their hearing aids, what  kinds of devices they used, or even if the participants were using  the right device for their diagnosis. And some scientists think it could take years  for the effect of hearing aids to kick in. So if people who just started wearing  hearing aids were mixed in with people who have been wearing them for years,  the results would be harder to interpret.

So at that point there was  a lot left to be understood about the role of hearing  aids in cognitive decline. And, good news, other studies  were already under way! In 2018, a study that followed up with  participants over 25 years concluded that people who wore hearing aids  were at lower risk of dementia.

Now, that study was based on how well  the participants thought they could hear, rather than performance in hearing tests. And while that metric is correlated  with hearing test outcomes, it’s not quite as empirical as tests  that define their exact decibel loss. So the perfect experiment  hasn’t been conducted yet.

But none of the studies conducted so far say that using hearing aids is worse than not using them. And dementia still isn’t reversible,  so if hearing loss is causing dementia, raising the hearing loss threshold and actually implementing the treatments  available could change lives. It’s a testament to modern medical research that we’re starting to figure out this relationship.

And you heard it here first. If you’re still watching at the end of this video, you probably agree that dementia and  memory loss need to be understood better. And if you want to understand memory in a new way, you can take the Brilliant course  on Artificial Neural Networks.

This course offers 28 interactive  lessons, including Long Short-Term Memory, which teaches you how models process new data by remembering what they just processed. Brilliant’s interactive courses  are made by dedicated math and science educators and lifelong  learners from MIT, Caltech, Duke, and more. But that doesn’t mean you have to be  a college student to keep learning.

Brilliant courses are designed  for people of all levels, so you can just jump in at any  point and work your way to mastery. Brilliant has supported SciShow videos  for years, including this video! And if you want to support Brilliant,  you can click the link in the description down below, which will give you 20%  off an annual Premium subscription.

Before you commit to a year of Brilliant, you can try it for free by using that  link or by visiting Brilliant.org/SciShow. [♪ OUTRO]