196 | Hearing Loss and Cognitive Decline – A Conversation With Dr. Jennifer Deal

Dr. Jennifer Deal, thanks so much for joining us on Nav Neuro.

Really excited to have you here with us.

Thanks so much for having me.

I'm, I'm really grateful to be here.

So we are talking today about hearing loss and cognitive decline with a focus on midlife and older adults.

To start, maybe we can briefly talk through the fundamentals of hearing, which is the process by which airwaves are transformed into electrochemical signals that can be interpreted by our brains with different vibrations being perceived as different sounds.

We have the outer ear that funnels sound waves into the ear canal, the bones in the middle ear that amplify and transmit the sound, and then the inner ear with the cochlea and its hair cells that transduce the mechanical energy into action potentials that can be interpreted by the brain.

And of course, there are lots of higher order neural processing that goes on so that we can differentiate and interpret various sounds.

But what other basic information should our listeners know about the mechanics of hearing in order to better understand the rest of the conversation today?

Yeah.

So I think you did a great job just kind of outlining the basic biology related to hearing.

I think what's really important when we start talking about hearing and its possible relationship with cognition and, and other outcomes as we age is to really recognize that hearing happens in two steps.

And so just as you mentioned, the first step is really kind of what happens in the ear, and that's where the sound is funneled in, um, and it's transmitted into a neural signal.

So that first step is really the encoding of important sound, um, by the cochlea in the inner ear, so that's the snail-shaped organ of hearing, um, into that neural signal, and then it's the neural signal that goes to the brain, and that's where the second step happens, is in the brain.

So first step in the ear and second step in the brain.

And so when we start talking about associations, we have to think really carefully about the pathways by which things might be associated.

We need to make sure that the measure of hearing matches our potential pathways by which hearing loss might be related to cognition.

So for example, um, if we're really interested in understanding what's happening in the ear, we should be choosing a measure where we're, um, actually capturing what's happening in the cochlea and not a measure, which we do have a lot of measures of hearing that actually relate more to what's happening, um, in the brain.

So that's I think something that's really important to keep in mind.

I think the other thing that's important to keep in mind is that when we start talking about hearing loss, we're not just talking about sounds being quieter.

We're actually talking about issues within the cochlea and challenges with encoding those-- that sound into a neural signal.

And that happens mostly because, um, the hair cells that we have in our inner ears over time, they degrade, and they don't come back.

So they're post-mitotic, so we're not able to regenerate them.

And so what that means is it's not just a question of sounds being quieter or sounding muffled.

It's actually a question more of clarity because the issue is with the encoding of sound.