Hearing Matters Podcast

Auditory Neuroplasticity with Dr. Brandon Paul

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Dr. Douglas Beck sits down with Dr. Brandon Paul to unravel the fascinating world of auditory neuroplasticity and its profound implications for hearing health. Dr. Paul shares cutting-edge research on how our brains adapt when hearing diminishes—and what happens when we restore that sensory input.

The conversation begins with a clear explanation of neuroplasticity as the brain's ability to reorganize itself throughout our lives, though most actively during early development. When hearing loss occurs, the brain doesn't simply accept reduced input. Instead, neurons become hyperactive through increased spontaneous firing, stronger responses to weak signals, and enhanced neural synchrony—all attempts to maintain their expected level of stimulation.

Most remarkable is the phenomenon called cross-modal plasticity. As auditory input decreases, visual processing intensifies in brain regions typically dedicated to hearing. Dr. Paul explains that this isn't a simple takeover but rather an unmasking of existing multisensory connections. Surprisingly, proper hearing aid fitting can reverse this process, normalizing both visual and auditory responses even in older adults.

The cognitive implications are significant. Untreated hearing loss forces the brain to rely heavily on internal templates rather than actual sensory input, creating opportunities for miscommunication and increasing cognitive load. This contributes to the well-documented connection between hearing loss and cognitive decline—a risk that multiplies dramatically when combined with untreated vision problems. 

Whether you're an audiologist, hearing care professional, or someone concerned about hearing health, this episode provides invaluable insights into why early intervention matters. The brain's remarkable adaptability offers hope that appropriate hearing technology can not only improve communication but potentially preserve cognitive function throughout life.

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Blaise M. Delfino, M.S. - HIS:

Thank you to our partners. Cycle, built for the entire hearing care practice. Redux, the best dryer, hands down Caption call by Sorenson. Life is calling CareCredit, here today to help more people hear tomorrow. Faderplugs the world's first custom adjustable earplug. Welcome back to another episode of the Hearing Matters Podcast. I'm founder and host Blaise Delfino and, as a friendly reminder, this podcast is separate from my work at Starkey.

Dr. Douglas L. Beck:

Good afternoon. This is Dr Douglas Beck with the Hearing Matters Podcast. We're here today with Dr Brandon Paul. He is an assistant professor in the Department of Psychology at Toronto Metropolitan University and adjunct scientist at Baycrest Hospital in Toronto. His research interests include neuroplasticity of the auditory system, sensory and cognitive effects of hearing loss and speech rehab in cochlear implant users and tinnitus. His work is supported by the National Science and Engineering Research Council in Canada, the Social Science and Research Council of Canada and the Canadian Foundation for Innovation. Boy, that's a mouthful. Did I get any of that right? You did, okay, good, nice to see you, brandon. Thanks for joining me. Thanks for having me. All right, you're entirely welcome. I want to start by defining neuroplasticity. What the heck is neuroplasticity?

Dr. Brandon Paul:

Neuroplasticity involves some sort of change in either the structure of the function of the nervous system due to things like experience or due when we learn new information, when we update our brains with information that comes through the senses or that we imagine or that we think about, then this can cause changes in the connections between neurons, and that is how we store information and use it in order to achieve our goals.

Dr. Douglas L. Beck:

Okay, that's pretty concise and just to be sure that I'm clear, my understanding of neuroplasticity is your central nervous system is essentially plastic, meaning changeable or malleable from the moment of birth until the moment of death, but it is much more malleable in the early years, perhaps through age five to seven, something like that. Is that true?

Dr. Brandon Paul:

That's correct. In early years there's a boatload of neuroplasticity that happens all across the nervous system as the brain sort of becomes attuned to its regularities and patterns that a young developing individual would be exposed to. But an interesting question is how much this neuroplasticity happens in later life, and this is sort of the topic of research questions that we're interested in doing specifically in aging and hearing loss, which is sort of a side research track that I'm on in addition to cochlear implant research.

Dr. Douglas L. Beck:

Yeah, and this is a huge question for all of science, because early on now I'm going to tell you my understanding. But I am not a neuroscientist you are, so please absolutely correct me. I read in a couple of different psychology books, in particular the third one by Dan Levitin, where he talks about when humans are born. You know, all senses are active and everything comes in light and sound and tactile and smells. And then for the first few weeks, months, maybe a year or two, we're actually pruning away those things to get sensory lines established such that sound is only going into the ear and through the eighth nerve, vision is only going in through the optic nerve and being processed in the occipital lobe, tactile etc. Is that correct? We spend a lot of that energy early on pruning out sensory information so we get line-labeled results, meaning vision is to the optic nerve, hearing is to the auditory nerve.

Dr. Brandon Paul:

Yeah, as far as the auditory and visual nerve are concerned, those things are, of course, connected to our or the apparatus that we have in the eyes and the apparatus that we have in the ears, the cortical regions, the brain regions themselves are the ones that we might think of as being tabula rasa.

Dr. Douglas L. Beck:

Yes, blank slates yeah.

Dr. Brandon Paul:

Right, and so the idea of synaptic and neuronal pruning that happens early in development is more concerned with sort of the cortical architecture that is plugged into the peripheral nerves from the eyes, the ears, the skin and so forth.

Dr. Douglas L. Beck:

So let's talk about what happens as somebody loses more and more hearing. They're getting less and less sensory input. And then let's talk about what happens if that person were to receive a cochlear implant.

Dr. Brandon Paul:

Certainly, there seems to be a number of different ways that the brain changes after a hearing loss or any sort of sensory loss. A few of the more notable things that can happen are, of course, you reduce sort of flow of information from the ear to the brain and as a result of this lack of information flow, there can be a number of things that happen. One of the more notable things that happens is neurons that have lost their connection to the ear can become hyperactive. Neurons like to have a set amount of input. They like the input that they get, and when they don't get that input, they may change their internal structure or they change their connections with other neurons so they can maintain the amount of input that they're used to.

Dr. Douglas L. Beck:

And that is essentially sensory recruitment, is it not?

Dr. Brandon Paul:

Yeah, a form of sensory recruitment, and this happens in many ways. This could be an increase in just a spontaneous activity of neurons.

Dr. Douglas L. Beck:

Yeah, with no stimuli, just trying to achieve stimulation.

Dr. Brandon Paul:

Exactly, or they have larger responses to any sort of incoming stimuli coming from the damaged sense.

Dr. Brandon Paul:

So if a sound comes into an ear with hearing loss, then some neurons might have an elevated response to this and because lower level neurons, let's say at the auditory nerve, aren't giving as strong of a signal. The third way that this may happen is that neurons that have lost their connection to whatever sense may become more synchronously active, and that is actually a key part to the hyperactivity puzzle that we're trying to figure out in brain plasticity after hearing loss, where it's not just that you have increased in spontaneous rates or stronger responses to stimulation, it's also a matter of how well they synchronize with other neurons too. So we see increased neural synchrony between neurons that may have lost their connection to the ear. All of this to me sounds like how each individual neuron might be trying to maintain the amount of input that it gets, whether that's from a different neuron, whether it's responding to weak signals coming in from the periphery, or whether it's having stronger excuse me or having more spontaneous firing rates or spontaneous activity that happened in the nervous system.

Dr. Douglas L. Beck:

Now I know it's off topic, but what you just said is kind of fascinating and I wonder how that feeds into the perception of tinnitus.

Dr. Brandon Paul:

Yeah, that's a separate side topic, and so there's a strong line of research that looks at whether one of these types or flavors of hyperactivity may be related to the tinnitus correlate. A lot of people have found correlations between tinnitus and hyperactivity in the auditory system. They see humans and animal models of tinnitus and as well, uh, how these neurons might respond to being plugged back into the ear.

Dr. Douglas L. Beck:

Let's say a cochlear implant.

Dr. Brandon Paul:

Does that bring down the hyperactivity now that we've restored some afferent or input coming from the ear and that that could be theoretically a hearing aid.

Dr. Douglas L. Beck:

that could be a cochlear implant, assistive device, over the counter device, anything that is now stimulating that auditory nerve. Right, correct, okay, so we have these effects and these are essentially afferent effects. Right, and then what happens if we were to take that auditory nerve which is no longer, let's say, the outer hair cells, the inner hair cells, no longer firing, but there's still a synaptic connection to the eighth nerve? So what would happen if you put a cochlear implant in many of these ears?

Dr. Brandon Paul:

So just to understand your question, is it about what happens to the neurons that are hyperactive if you plug them back into, let's say, if you reafferent them? Yes, exactly.

Dr. Brandon Paul:

A number of things could happen. It depends on what the state of that neuron might be, and now I'm starting to get into more theoretical waters rather than having harder evidence for this. So maybe a little bit of speculation here. But some neurons might maintain hyperactivity. They may not respond to that reaffirmation. Other neurons may do that Right, and so there's, there may be some sort of reorganization that happens when you restore the connection to the ear. Part of that has to deal with that.

Dr. Brandon Paul:

Even those, these technologies like cochlear implants and hearing aids are wonderful. It's not a perfect restoration of the auditory system. There's still some sort of issues with the type of information coming in if frequency selectivity is a little bit lower in hearing aids and you don't really have much frequency selectivity in cochlear implants. So there's still, even though it's hearing restoration, it's partial hearing restoration and for that reason some neurons might come back to how they typically operate. Some neurons might maintain hyperactivity. Some neurons may search for other inputs from other senses, which is a main topic that I think that we'll get to whether some neurons might start responding to vision or might start responding to our tactile or our touch system.

Dr. Douglas L. Beck:

So this is so interesting because, in my mind, the first time I really gave this a lot of thought was the paper on cross-modal activity by Hannah Glick and Anu Sharma. I want to say that was about seven or eight years ago and here's my interpretation of what they said. So as people develop more and more hearing loss, their auditory brainstem response became less and less because the ear was transmitting less and less information to the brain. Interestingly, they noticed that as that was happening, the visual evoked potential was becoming larger and larger. So I think this talks to the cross-modal shift that you're addressing. And then the most interesting factor to me was that after they fitted the patients with appropriately fitted prescription hearing aids premium hearing aids the visual evoked potential got smaller and smaller and smaller, went back to normal and the auditory evoked potential became larger, larger, larger. So, based on that, first of all, is my understanding correct on that study?

Dr. Brandon Paul:

Yes, I think. Yeah, the Glick and Sharma paper from 2020,. Yeah, a new Sharma strip in Colorado. She's done a number of really great research studies on what we would consider cross-modal plasticity in partial hearing loss or age-related hearing loss, and the main finding is with more hearing loss, then you have larger or earlier visual evoked potentials.

Dr. Brandon Paul:

is with more hearing loss. Then you have larger or earlier visual evoked potentials. So you flash an image on the screen that's maybe like a low-level checkerboard or some sort of concentric circles or something like this, and then you see the brain response to the flash of that image is much larger or faster.

Dr. Brandon Paul:

And then after hearing aid use, then you sort of reverse this, and so it seems like this cross-modal plasticity is a reversible process which is astonishing really, absolutely. It just speaks to the remarkable ability of the nervous system to adapt to its sensory experiences, or its sensory abilities.

Dr. Douglas L. Beck:

Yeah, because we used to say, you know, when I was working on my master's, oh gosh, there were still some little dinosaurs around. But when I was doing that work, what we used to say, you know, was with neural systems it was use it or lose it, same as motoric systems, you know. And if you didn't exercise those neurons and you didn't exercise those muscles, they would fade away. And what we're learning now is that neuroplasticity is reversible in some situations, in some pathways.

Dr. Brandon Paul:

And an interesting finding from the study that you had mentioned, from Hannah Glick and Anu Sharma. We actually have a paper that's about to be pre-printed that sort of corroborates those findings. The work I'm doing at Toronto Metropolitan University is more on age-related hearing loss compared to the work at Sunnybrook Hospital in Toronto, which is more on cochlear implant users. Sure, as the question that we opened with which was does this neuroplasticity happen in late life, in aging, in older adults? And it seems to be yes.

Dr. Douglas L. Beck:

That is the answer to that. Both our group and Anusha Arman's group have found similar results. Yeah, and I suspect that in older adults I say that as an older adult it takes a lot more effort to build muscle, effort to build muscle.

Dr. Brandon Paul:

It takes a lot more effort to train neurons particularly, I would guess that efferent nervous system is very difficult to challenge, very difficult to test the efferent nervous system. We don't know a lot about neuroplasticity in those descending pathways, and so that is really an open question for us researchers to address in the future.

Dr. Douglas L. Beck:

In some research papers. What I've noticed is that as hearing degrades over time, certainly other parts of the brain will try to take over the superior temporal lobe, or Brodmann area 4142, or Heschel's gyrus, any of that it's all pretty much the same. But as we lose hearing, as we lose sensory input you mentioned that vision might take over that. What I always heard early on was that it was somatosensory that would take over that superior temporal lobe. What is the current understanding on that?

Dr. Brandon Paul:

Great question. The historical textbook view, based upon studies that happened 20, 25 years ago, was that, let's say, if you had complete sensory loss, total blindness or total deafness this happens usually in congenital cases, so early in life or at birth the old prevailing view was that the deafferented cortex and by that I mean, let's say, if it's auditory cortex in cases of deafness that this might become a battleground for other senses Like oh, these neurons are no longer getting input from the ear and even parietal could take some of it.

Dr. Brandon Paul:

It could be remapped to vision, it could be remapped to touch. So it turns out that's probably an inaccurate view on what is actually happening and usually we think about historically, maybe neurons and auditory cortex being involved in auditory processes and neurons.

Dr. Douglas L. Beck:

Yeah, exactly.

Dr. Brandon Paul:

Vice versa or similarly. But we really need to think about how some of the connections actually exist in those regions and mostly what we should think about is that those brain areas are essentially, or especially, ones that are not in the core. Regions like the auditory core, the visual core, are multisensory, and what I mean by that is cortical auditory regions that are not in primary auditory cortex, but we might call secondary or non-primary regions, receive a lot of inputs from non-auditory sources like the visual system.

Dr. Douglas L. Beck:

Yeah, sure.

Dr. Brandon Paul:

And so there's already pre-existing inputs to those neurons from touch and from vision, but they're masked or covered up because the auditory information that's coming in is what those neurons are most strongly responding to. When you lose your auditory input now, those weak inputs can now start responding to vision or touch. And this is more probably accurate of what this sort of cross-modal plasticity might be. And it's a dynamic and fluid process. It's not necessarily this large battleground where neurons can completely change their function. They change their computational ability. It's more about the up-regulation and down-regulation of their inputs.

Dr. Douglas L. Beck:

And does most of this occur in the thalamus, or am I way off base?

Dr. Brandon Paul:

There's currently research that's sort of debating whether these sort of changes in the drive to these neurons whether visual auditory happens through thalamocortical pathway, so coming from the thalamus to the cortex, or whether it's corticocortical, so from auditory cortex to visual cortex or vice versa. There probably is contributions from both. And the last thing I would like to mention is that there's probably some sort of top-down cognitive involvement as a part of this driving what neurons are responding to which sense, and so it's not just a purely sensory phenomenon but it may have the goals of the individual, whether that's visual or auditory.

Dr. Douglas L. Beck:

All right, and I'm with you on all of that. Let me ask you a question then. Supposing that you have untreated vision loss, what happens to the optic nerve and the occipital lobe?

Dr. Brandon Paul:

The optic nerve itself. I'm not a vision scientist, so this is just from my general knowledge from reading. Similar to the auditory system, the visual system will upregulate auditory behaviors upon situations of blindness or partial vision loss.

Dr. Douglas L. Beck:

Into the visual system. That's correct.

Dr. Brandon Paul:

Yeah, non-primary regions, where the regions that sort of have both visual and auditory interactions, are the ones where there's a lot of this give and take of what input is stronger, what input is weaker.

Dr. Douglas L. Beck:

So what I'd like to ask you. I want to go specifically now to issues in cognition, because your paper I actually saw this online and that's why I contacted you it was in Canadian audiologists and it was to the brain and back the role of visual neuroplasticity in cochlear implant users' speech outcomes. So we've got that. But in there, within that paper, you talked a little bit about cognitive effects of cochlear implant and I think we've known for, I want to say, eight or 10 years that people who get cochlear implants do improve their cognitive ability. Can you address that for me?

Dr. Brandon Paul:

Yeah, and this is the research that we had done with cochlear implants and sort of cognitive ability was more along the lines of selective attention and working memory. But as far as long-term cognitive changes are concerned, my understanding is that, yes, we know that there are maybe effects or alterations to certain cognitive abilities with hearing loss, and some of those might be remedied after cochlear implantation and hearing aid use, specifically, with respect, most acutely I should say, with things like working memory and attention while somebody's listening to speech, especially in noisy environments. But open question still, and there's some evidence to suggest that maybe long-term memory could be affected by hearing loss that could be remedied by using hearing aids or cochlear implants. The effects of these things are still debated, to which cognitive functions and whether or not there are truly neuroprotective effects of hearing aid or cochlear implant use still are being worked out. But there's still we have to acknowledge the preliminary evidence that suggests there are definitely some benefits.

Dr. Douglas L. Beck:

Yeah, I think that's clear. And even in the dual sensory loss literature I read recently and this is a paper I think came out in 2025, probably about two or three weeks ago and the authors were saying that if you have visual loss, you know you're at a higher risk for cognitive decline. If you have auditory attenuation degradation, you're at risk for cognitive decline. If you have both untreated vision, untreated hearing, you're at eight times the risk for cognitive decline. I mean, it's pretty substantial, significantly. Yes, yeah, yeah. And what about? So? This is my understanding. This is a weird little topic, but I'll do my best to word this appropriately and and so that I can ask you this question.

Dr. Douglas L. Beck:

My understanding is, as hearing degrades over time, the brain is getting less and less auditory information. The information it gets is lesser in loudness. Of course, it's missing spectral components. It's missing spectral components, it's missing timing, because the timing is screwed up by the sensory neural loss. We have all sorts of degradation going on and the bits that are coming through now becomes the new signals that the brain has, and the brain, because it is plastic, starts to accept that mushy signal as the essence of normal and then it changes as a result of that. What do you think about that?

Dr. Brandon Paul:

Yeah, I would say that's a good characterization of it.

Dr. Brandon Paul:

Through someone's earlier parts of their life, let's say when their sensory abilities are more normal, they've developed these sets of experiences that form templates that whenever somebody is listening to somebody speak, they have some knowledge about language, they have some knowledge about how the speech sounds should appear.

Dr. Brandon Paul:

There's a lot of variation in how those speech sounds might appear, but we have a template of what these speech sounds might be, exactly A process of matching whatever comes from the ear to those stored templates.

Dr. Brandon Paul:

Now, the templates are usually maintained by a consistent matching of the sensory input to whatever we have in the brain, and if the sensory abilities decline with age or a number of other factors that we're aware of, then it becomes harder and harder or more difficult to match these sensory inputs to those stored templates. But it's still possible and it's still it is possible to get used to that, because you may hook on to useful cues or parts of speech that you know you have maybe a good template for and you can maybe use heuristics I'm paying attention to this prosodic element or I'm paying attention to the syllabic rate or something like that in order to achieve this template matching procedure. But the question is does there become a point where there's so much reliance on the internal templates because the input signal is so degraded that how does this change cognition, which seems to be your question, exactly right.

Dr. Brandon Paul:

Yes, you said it much better than I did, but that's exactly right, no, problem the issue becomes is that there's a lot more opportunity to mishear input or signals or speech coming in from the periphery because you're so reliant on what that template might be. And not only are there sometimes template mismatches that lead to errors in perception, is that your confidence in what you're hearing is also pretty high. It's like no, I didn't mishear you. It's like I know what I believe I heard, because there's a lot more reliance on the template, the stored knowledge, rather than paying attention to the sensory input coming in.

Dr. Brandon Paul:

And if it's the case that you're more relying on your internal model of what this language might be and you're not getting reinforcement for that model from the periphery, from the environment, from the external world, then this can open up opportunities for, maybe, alterations in cognition. Maybe it's going to impact your social communication dynamics where it's harder to maintain social bonds. Maybe, if you're trying to achieve some sort of goal in society going to the bank, going to the grocery store and so forth the sort of dynamic interactions that you need to have there using your language system become more difficult, and so that puts strain on social relationships, which puts further strain on cognitive ability, major feedback loop that you get stuck in and, as a result, then this could degrade or decline cognition. That's the theory, of course, rather than having hard evidence for this, but this seems to be a way that you can put together the available research in order to understand, maybe, how cognition changes as a result of degraded hearing, when we're specifically talking about speech and language.

Dr. Douglas L. Beck:

That's fantastic, all right. Well, dr Paul, you've been very generous with your time. I appreciate it so much. I think your explanations make very difficult subjects much more clear, and I appreciate that. Thank you so much for joining us.

Dr. Brandon Paul:

Thanks for having me, doug, I really appreciate it, and thanks to all your listeners for tuning in.

Dr. Douglas L. Beck:

I appreciate it, thank you.

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Blaise M. Delfino, M.S. - HIS

Host
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Dr. Douglas Beck

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