March 20, 2025 • 24 mins
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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Episode Transcript
Available transcripts are automatically generated. Complete accuracy is not guaranteed.
Blaise M. Delfino, M.S. - (00:19):
Thank you to our partners.
Cycle, built for the entirehearing care practice.
Redux, the best dryer, handsdown Caption call by Sorenson.
Life is calling CareCredit,here today to help more people
hear tomorrow.
Faderplugs the world's firstcustom adjustable earplug.
(00:41):
Welcome back to another episodeof the Hearing Matters Podcast.
I'm founder and host BlaiseDelfino and, as a friendly
reminder, this podcast isseparate from my work at Starkey
.
Dr. Douglas L. Beck (00:56):
Good afternoon.
This is Dr Douglas Beck withthe Hearing Matters Podcast.
We're here today with DrBrandon Paul.
He is an assistant professor inthe Department of Psychology at
Toronto Metropolitan Universityand adjunct scientist at
Baycrest Hospital in Toronto.
His research interests includeneuroplasticity of the auditory
system, sensory and cognitiveeffects of hearing loss and
(01:18):
speech rehab in cochlear implantusers and tinnitus.
His work is supported by theNational Science and Engineering
Research Council in Canada, theSocial Science and Research
Council of Canada and theCanadian Foundation for
Innovation.
Boy, that's a mouthful.
Did I get any of that right?
You did, okay, good, nice tosee you, brandon.
Thanks for joining me.
Thanks for having me.
(01:39):
All right, you're entirelywelcome.
I want to start by definingneuroplasticity.
What the heck isneuroplasticity?
Dr. Brandon Pau (01:46):
Neuroplasticity involves some sort of change in
either the structure of thefunction of the nervous system
due to things like experience ordue when we learn new
information, when we update ourbrains with information that
(02:07):
comes through the senses or thatwe imagine or that we think
about, then this can causechanges in the connections
between neurons, and that is howwe store information and use it
in order to achieve our goals.
Dr. Douglas L. Beck (02:19):
Okay, that's pretty concise and just
to be sure that I'm clear, myunderstanding of neuroplasticity
is your central nervous systemis essentially plastic, meaning
changeable or malleable from themoment of birth until the
moment of death, but it is muchmore malleable in the early
years, perhaps through age fiveto seven, something like that.
(02:40):
Is that true?
Dr. Brandon Paul (02:41):
That's correct .
In early years there's aboatload of neuroplasticity that
happens all across the nervoussystem as the brain sort of
becomes attuned to itsregularities and patterns that a
young developing individualwould be exposed to.
But an interesting question ishow much this neuroplasticity
happens in later life, and thisis sort of the topic of research
questions that we're interestedin doing specifically in aging
(03:04):
and hearing loss, which is sortof a side research track that
I'm on in addition to cochlearimplant research.
Dr. Douglas L. Beck (03:10):
Yeah, and this is a huge question for all
of science, because early on nowI'm going to tell you my
understanding.
But I am not a neuroscientistyou are, so please absolutely
correct me.
I read in a couple of differentpsychology books, in particular
the third one by Dan Levitin,where he talks about when humans
(03:33):
are born.
You know, all senses are activeand everything comes in light
and sound and tactile and smells.
And then for the first fewweeks, months, maybe a year or
two, we're actually pruning awaythose things to get sensory
lines established such thatsound is only going into the ear
and through the eighth nerve,vision is only going in through
the optic nerve and beingprocessed in the occipital lobe,
(03:54):
tactile etc.
Is that correct?
We spend a lot of that energyearly on pruning out sensory
information so we getline-labeled results, meaning
vision is to the optic nerve,hearing is to the auditory nerve
.
Dr. Brandon Paul (04:08):
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 inthe eyes and the apparatus that
we have in the ears, thecortical regions, the brain
regions themselves are the onesthat we might think of as being
tabula rasa.
Dr. Douglas L. Beck (04:23):
Yes, blank slates yeah.
Dr. Brandon Paul (04:25):
Right, and so the idea of synaptic and
neuronal pruning that happensearly in development is more
concerned with sort of thecortical architecture that is
plugged into the peripheralnerves from the eyes, the ears,
the skin and so forth.
Dr. Douglas L. Beck (04:39):
So let's talk about what happens as
somebody loses more and morehearing.
They're getting less and lesssensory input.
And then let's talk about whathappens if that person were to
receive a cochlear implant.
Dr. Brandon Paul (04:51):
Certainly, there seems to be a number of
different ways that the brainchanges after a hearing loss or
any sort of sensory loss.
A few of the more notablethings that can happen are, of
course, you reduce sort of flowof information from the ear to
the brain and as a result ofthis lack of information flow,
there can be a number of thingsthat happen.
One of the more notable thingsthat happens is neurons that
(05:14):
have lost their connection tothe ear can become hyperactive.
Neurons like to have a setamount of input.
They like the input that theyget, and when they don't get
that input, they may changetheir internal structure or they
change their connections withother neurons so they can
maintain the amount of inputthat they're used to.
Dr. Douglas L. Beck (05:31):
And that is essentially sensory recruitment
, is it not?
Dr. Brandon Paul (05:34):
Yeah, a form of sensory recruitment, and this
happens in many ways.
This could be an increase injust a spontaneous activity of
neurons.
Dr. Douglas L. Beck (05:41):
Yeah, with no stimuli, just trying to
achieve stimulation.
Dr. Brandon Paul (05:45):
Exactly, or they have larger responses to
any sort of incoming stimulicoming from the damaged sense.
So if a sound comes into an earwith hearing loss, then some
neurons might have an elevatedresponse to this and because
lower level neurons, let's sayat the auditory nerve, aren't
giving as strong of a signal.
The third way that this mayhappen is that neurons that have
(06:05):
lost their connection towhatever sense may become more
synchronously active, and thatis actually a key part to the
hyperactivity puzzle that we'retrying to figure out in brain
plasticity after hearing loss,where it's not just that you
have increased in spontaneousrates or stronger responses to
stimulation, it's also a matterof how well they synchronize
(06:28):
with other neurons too.
So we see increased neuralsynchrony between neurons that
may have lost their connectionto the ear.
All of this to me sounds likehow each individual neuron might
be trying to maintain theamount of input that it gets,
whether that's from a differentneuron, whether it's responding
to weak signals coming in fromthe periphery, or whether it's
(06:49):
having stronger excuse me orhaving more spontaneous firing
rates or spontaneous activitythat happened in the nervous
system.
Dr. Douglas L. Beck (06:56):
Now I know it's off topic, but what you
just said is kind of fascinatingand I wonder how that feeds
into the perception of tinnitus.
Dr. Brandon Paul (07:04):
Yeah, that's a separate side topic, and so
there's a strong line ofresearch that looks at whether
one of these types or flavors ofhyperactivity may be related to
the tinnitus correlate.
A lot of people have foundcorrelations between tinnitus
and hyperactivity in theauditory system.
They see humans and animalmodels of tinnitus and as well,
(07:26):
uh, how these neurons mightrespond to being plugged back
into the ear.
Dr. Douglas L. Beck (07:31):
Let's say a cochlear implant.
Dr. Brandon Paul (07:33):
Does that bring down the hyperactivity now
that we've restored someafferent or input coming from
the ear and that that could betheoretically a hearing aid.
Dr. Douglas L. Beck (07:42):
that could be a cochlear implant, assistive
device, over the counter device, anything that is now
stimulating that auditory nerve.
Right, correct, okay, so wehave these effects and these are
essentially afferent effects.
Right, and then what happens ifwe were to take that auditory
nerve which is no longer, let'ssay, the outer hair cells, the
(08:04):
inner hair cells, no longerfiring, but there's still a
synaptic connection to theeighth nerve?
So what would happen if you puta cochlear implant in many of
these ears?
Dr. Brandon Paul (08:14):
So just to understand your question, is it
about what happens to theneurons that are hyperactive if
you plug them back into, let'ssay, if you reafferent them?
Yes, exactly.
A number of things could happen.
It depends on what the state ofthat neuron might be, and now
I'm starting to get into moretheoretical waters rather than
having harder evidence for this.
So maybe a little bit ofspeculation here.
But some neurons might maintainhyperactivity.
(08:36):
They may not respond to thatreaffirmation.
Other neurons may do that Right, and so there's, there may be
some sort of reorganization thathappens when you restore the
connection to the ear.
Part of that has to deal withthat.
Even those, these technologieslike cochlear implants and
hearing aids are wonderful.
It's not a perfect restorationof the auditory system.
There's still some sort ofissues with the type of
(08:59):
information coming in iffrequency selectivity is a
little bit lower in hearing aidsand you don't really have much
frequency selectivity incochlear implants.
So there's still, even thoughit's hearing restoration, it's
partial hearing restoration andfor that reason some neurons
might come back to how theytypically operate.
Some neurons might maintainhyperactivity.
Some neurons may search forother inputs from other senses,
(09:20):
which is a main topic that Ithink that we'll get to whether
some neurons might startresponding to vision or might
start responding to our tactileor our touch system.
Dr. Douglas L. Beck (09:30):
So this is so interesting because, in my
mind, the first time I reallygave this a lot of thought was
the paper on cross-modalactivity by Hannah Glick and Anu
Sharma.
I want to say that was aboutseven or eight years ago and
here's my interpretation of whatthey said.
So as people develop more andmore hearing loss, their
auditory brainstem responsebecame less and less because the
(09:53):
ear was transmitting less andless information to the brain.
Interestingly, they noticedthat as that was happening, the
visual evoked potential wasbecoming larger and larger.
So I think this talks to thecross-modal shift that you're
addressing.
And then the most interestingfactor to me was that after they
fitted the patients withappropriately fitted
(10:15):
prescription hearing aidspremium hearing aids the visual
evoked potential got smaller andsmaller and smaller, went back
to normal and the auditoryevoked potential became larger,
larger, larger.
So, based on that, first of all, is my understanding correct on
that study?
Dr. Brandon Paul (10:30):
Yes, I think.
Yeah, the Glick and Sharmapaper from 2020,.
Yeah, a new Sharma strip inColorado.
She's done a number of reallygreat research studies on what
we would consider cross-modalplasticity in partial hearing
loss or age-related hearing loss, and the main finding is with
more hearing loss, then you havelarger or earlier visual evoked
potentials.
(10:50):
is with more hearing loss.
Then you have larger or earliervisual evoked potentials.
So you flash an image on thescreen that's maybe like a
low-level checkerboard or somesort of concentric circles or
something like this, and thenyou see the brain response to
the flash of that image is muchlarger or faster.
And then after hearing aid use,then you sort of reverse this,
and so it seems like thiscross-modal plasticity is a
reversible process which isastonishing really, absolutely.
(11:13):
It just speaks to theremarkable ability of the
nervous system to adapt to itssensory experiences, or its
sensory abilities.
Dr. Douglas L. Beck (11:18):
Yeah, because we used to say, you know
, when I was working on mymaster's, oh gosh, there were
still some little dinosaursaround.
But when I was doing that work,what we used to say, you know,
was with neural systems it wasuse it or lose it, same as
motoric systems, you know.
And if you didn't exercisethose neurons and you didn't
exercise those muscles, theywould fade away.
(11:40):
And what we're learning now isthat neuroplasticity is
reversible in some situations,in some pathways.
Dr. Brandon Paul (11:48):
And an interesting finding from the
study that you had mentioned,from Hannah Glick and Anu Sharma
.
We actually have a paper that'sabout to be pre-printed that
sort of corroborates thosefindings.
The work I'm doing at TorontoMetropolitan University is more
on age-related hearing losscompared to the work at
Sunnybrook Hospital in Toronto,which is more on cochlear
implant users.
Sure, as the question that weopened with which was does this
(12:10):
neuroplasticity happen in latelife, in aging, in older adults?
And it seems to be yes.
Dr. Douglas L. Beck (12:20):
That is the answer to that.
Both our group and AnushaArman's group have found similar
results.
Yeah, and I suspect that inolder adults I say that as an
older adult it takes a lot moreeffort to build muscle, effort
to build muscle.
Dr. Brandon Paul (12:27):
It takes a lot more effort to train neurons
particularly, I would guess thatefferent nervous system is very
difficult to challenge, verydifficult to test the efferent
nervous system.
We don't know a lot aboutneuroplasticity in those
descending pathways, and so thatis really an open question for
us researchers to address in thefuture.
Dr. Douglas L. Beck (12:48):
In some research papers.
What I've noticed is that ashearing degrades over time,
certainly other parts of thebrain will try to take over the
superior temporal lobe, orBrodmann area 4142, or Heschel's
gyrus, any of that it's allpretty much the same.
But as we lose hearing, as welose sensory input you mentioned
that vision might take overthat.
(13:10):
What I always heard early onwas that it was somatosensory
that would take over thatsuperior temporal lobe.
What is the currentunderstanding on that?
Dr. Brandon Paul (13:19):
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 ortotal deafness this happens
usually in congenital cases, soearly in life or at birth the
old prevailing view was that thedeafferented cortex and by that
(13:40):
I mean, let's say, if it'sauditory cortex in cases of
deafness that this might becomea battleground for other senses
Like oh, these neurons are nolonger getting input from the
ear and even parietal could takesome of it.
It could be remapped to vision,it could be remapped to touch.
So it turns out that's probablyan inaccurate view on what is
actually happening and usuallywe think about historically,
(14:00):
maybe neurons and auditorycortex being involved in
auditory processes and neurons.
Dr. Douglas L. Beck (14:05):
Yeah, exactly.
Dr. Brandon Paul (14:06):
Vice versa or similarly.
But we really need to thinkabout how some of the
connections actually exist inthose regions and mostly what we
should think about is thatthose brain areas are
essentially, or especially, onesthat are not in the core.
Regions like the auditory core,the visual core, are
multisensory, and what I mean bythat is cortical auditory
regions that are not in primaryauditory cortex, but we might
(14:29):
call secondary or non-primaryregions, receive a lot of inputs
from non-auditory sources likethe visual system.
Dr. Douglas L. Beck (14:35):
Yeah, sure.
Dr. Brandon Paul (14:40):
And so there's already pre-existing inputs to
those neurons from touch andfrom vision, but they're masked
or covered up because theauditory information that's
coming in is what those neuronsare most strongly responding to.
When you lose your auditoryinput now, those weak inputs can
now start responding to visionor touch.
And this is more probablyaccurate of what this sort of
(15:03):
cross-modal plasticity might be.
And it's a dynamic and fluidprocess.
It's not necessarily this largebattleground where neurons can
completely change their function.
They change their computationalability.
It's more about theup-regulation and
down-regulation of their inputs.
Dr. Douglas L. Beck (15:20):
And does most of this occur in the
thalamus, or am I way off base?
Dr. Brandon Paul (15:24):
There's currently research that's sort
of debating whether these sortof changes in the drive to these
neurons whether visual auditoryhappens through thalamocortical
pathway, so coming from thethalamus to the cortex, or
whether it's corticocortical, sofrom auditory cortex to visual
cortex or vice versa.
There probably is contributionsfrom both.
And the last thing I would liketo mention is that there's
(15:47):
probably some sort of top-downcognitive involvement as a part
of this driving what neurons areresponding to which sense, and
so it's not just a purelysensory phenomenon but it may
have the goals of the individual, whether that's visual or
auditory.
Dr. Douglas L. Beck (16:02):
All right, and I'm with you on all of that.
Let me ask you a question then.
Supposing that you haveuntreated vision loss, what
happens to the optic nerve andthe occipital lobe?
Dr. Brandon Paul (16:13):
The optic nerve itself.
I'm not a vision scientist, sothis is just from my general
knowledge from reading.
Similar to the auditory system,the visual system will
upregulate auditory behaviorsupon situations of blindness or
partial vision loss.
Dr. Douglas L. Beck (16:27):
Into the visual system.
That's correct.
Dr. Brandon Paul (16:33):
Yeah, non-primary regions, where the
regions that sort of have bothvisual and auditory interactions
, are the ones where there's alot of this give and take of
what input is stronger, whatinput is weaker.
Dr. Douglas L. Beck (16:44):
So what I'd like to ask you.
I want to go specifically nowto issues in cognition, because
your paper I actually saw thisonline and that's why I
contacted you it was in Canadianaudiologists and it was to the
brain and back the role ofvisual neuroplasticity in
cochlear implant users' speechoutcomes.
(17:04):
So we've got that.
But in there, within that paper, you talked a little bit about
cognitive effects of cochlearimplant and I think we've known
for, I want to say, eight or 10years that people who get
cochlear implants do improvetheir cognitive ability.
Can you address that for me?
Dr. Brandon Paul (17:22):
Yeah, and this is the research that we had
done with cochlear implants andsort of cognitive ability was
more along the lines ofselective attention and working
memory.
But as far as long-termcognitive changes are concerned,
my understanding is that, yes,we know that there are maybe
effects or alterations tocertain cognitive abilities with
hearing loss, and some of thosemight be remedied after
(17:43):
cochlear implantation andhearing aid use, specifically,
with respect, most acutely Ishould say, with things like
working memory and attentionwhile somebody's listening to
speech, especially in noisyenvironments.
But open question still, andthere's some evidence to suggest
that maybe long-term memorycould be affected by hearing
(18:04):
loss that could be remedied byusing hearing aids or cochlear
implants.
The effects of these things arestill debated, to which
cognitive functions and whetheror not there are truly
neuroprotective effects ofhearing aid or cochlear implant
use still are being worked out.
But there's still we have toacknowledge the preliminary
evidence that suggests there aredefinitely some benefits.
Dr. Douglas L. Beck (18:22):
Yeah, I think that's clear.
And even in the dual sensoryloss literature I read recently
and this is a paper I think cameout in 2025, probably about two
or three weeks ago and theauthors were saying that if you
have visual loss, you knowyou're at a higher risk for
cognitive decline.
If you have auditoryattenuation degradation, you're
(18:42):
at risk for cognitive decline.
If you have both untreatedvision, untreated hearing,
you're at eight times the riskfor 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 Ican ask you this question.
(19:06):
My understanding is, as hearingdegrades over time, the brain is
getting less and less auditoryinformation.
The information it gets islesser in loudness.
Of course, it's missingspectral components.
It's missing spectralcomponents, it's missing timing,
because the timing is screwedup by the sensory neural loss.
We have all sorts ofdegradation going on and the
bits that are coming through nowbecomes the new signals that
(19:28):
the brain has, and the brain,because it is plastic, starts to
accept that mushy signal as theessence of normal and then it
changes as a result of that.
What do you think about that?
Dr. Brandon Paul (19:42):
Yeah, I would say that's a good
characterization of it.
Through someone's earlier partsof their life, let's say when
their sensory abilities are morenormal, they've developed these
sets of experiences that formtemplates that whenever somebody
is listening to somebody speak,they have some knowledge about
language, they have someknowledge about how the speech
(20:03):
sounds should appear.
There's a lot of variation inhow those speech sounds might
appear, but we have a templateof what these speech sounds
might be, exactly A process ofmatching whatever comes from the
ear to those stored templates.
Now, the templates are usuallymaintained by a consistent
matching of the sensory input towhatever we have in the brain,
(20:25):
and if the sensory abilitiesdecline with age or a number of
other factors that we're awareof, then it becomes harder and
harder or more difficult tomatch these sensory inputs to
those stored templates.
But it's still possible andit's still it is possible to get
used to that, because you mayhook on to useful cues or parts
(20:47):
of speech that you know you havemaybe a good template for and
you can maybe use heuristics I'mpaying attention to this
prosodic element or I'm payingattention to the syllabic rate
or something like that in orderto achieve this template
matching procedure.
But the question is does therebecome a point where there's so
(21:07):
much reliance on the internaltemplates because the input
signal is so degraded that howdoes this change cognition,
which seems to be your question,exactly right.
Yes, you said it much betterthan I did, but that's exactly
right, no, problem the issuebecomes is that there's a lot
more opportunity to mishearinput or signals or speech
coming in from the peripherybecause you're so reliant on
(21:29):
what that template might be.
And not only are theresometimes template mismatches
that lead to errors inperception, is that your
confidence in what you'rehearing is also pretty high.
It's like no, I didn't mishearyou.
It's like I know what I believeI heard, because there's a lot
more reliance on the template,the stored knowledge, rather
than paying attention to thesensory input coming in.
(21:49):
And if it's the case that you'remore relying on your internal
model of what this languagemight be and you're not getting
reinforcement for that modelfrom the periphery, from the
environment, from the externalworld, then this can open up
opportunities for, maybe,alterations in cognition.
Maybe it's going to impact yoursocial communication dynamics
(22:11):
where it's harder to maintainsocial bonds.
Maybe, if you're trying toachieve some sort of goal in
society going to the bank, goingto the grocery store and so
forth the sort of dynamicinteractions that you need to
have there using your languagesystem become more difficult,
and so that puts strain onsocial relationships, which puts
further strain on cognitiveability, major feedback loop
(22:33):
that you get stuck in and, as aresult, then this could degrade
or decline cognition.
That's the theory, of course,rather than having hard evidence
for this, but this seems to bea way that you can put together
the available research in orderto understand, maybe, how
cognition changes as a result ofdegraded hearing, when we're
specifically talking aboutspeech and language.
Dr. Douglas L. Beck (22:52):
That's fantastic, all right.
Well, dr Paul, you've been verygenerous with your time.
I appreciate it so much.
I think your explanations makevery difficult subjects much
more clear, and I appreciatethat.
Thank you so much for joiningus.
Dr. Brandon Paul (23:05):
Thanks for having me, doug, I really
appreciate it, and thanks to allyour listeners for tuning in.
Dr. Douglas L. Beck (23:10):
I appreciate it, thank you.
Thank you to our partners.
Cycle, built for the entirehearing care practice.
Redux, the best dryer, handsdown Caption call by Sorenson.
Life is calling CareCredit,here today to help more people
hear tomorrow.
Faderplugs the world's firstcustom adjustable earplug.
(00:41):
Welcome back to another episodeof the Hearing Matters Podcast.
I'm founder and host BlaiseDelfino and, as a friendly
reminder, this podcast isseparate from my work at Starkey
.
Dr. Douglas L. Beck (00:56):
Good afternoon.
This is Dr Douglas Beck withthe Hearing Matters Podcast.
We're here today with DrBrandon Paul.
He is an assistant professor inthe Department of Psychology at
Toronto Metropolitan Universityand adjunct scientist at
Baycrest Hospital in Toronto.
His research interests includeneuroplasticity of the auditory
system, sensory and cognitiveeffects of hearing loss and
(01:18):
speech rehab in cochlear implantusers and tinnitus.
His work is supported by theNational Science and Engineering
Research Council in Canada, theSocial Science and Research
Council of Canada and theCanadian Foundation for
Innovation.
Boy, that's a mouthful.
Did I get any of that right?
You did, okay, good, nice tosee you, brandon.
Thanks for joining me.
Thanks for having me.
(01:39):
All right, you're entirelywelcome.
I want to start by definingneuroplasticity.
What the heck isneuroplasticity?
Dr. Brandon Pau (01:46):
Neuroplasticity involves some sort of change in
either the structure of thefunction of the nervous system
due to things like experience ordue when we learn new
information, when we update ourbrains with information that
(02:07):
comes through the senses or thatwe imagine or that we think
about, then this can causechanges in the connections
between neurons, and that is howwe store information and use it
in order to achieve our goals.
Dr. Douglas L. Beck (02:19):
Okay, that's pretty concise and just
to be sure that I'm clear, myunderstanding of neuroplasticity
is your central nervous systemis essentially plastic, meaning
changeable or malleable from themoment of birth until the
moment of death, but it is muchmore malleable in the early
years, perhaps through age fiveto seven, something like that.
(02:40):
Is that true?
Dr. Brandon Paul (02:41):
That's correct .
In early years there's aboatload of neuroplasticity that
happens all across the nervoussystem as the brain sort of
becomes attuned to itsregularities and patterns that a
young developing individualwould be exposed to.
But an interesting question ishow much this neuroplasticity
happens in later life, and thisis sort of the topic of research
questions that we're interestedin doing specifically in aging
(03:04):
and hearing loss, which is sortof a side research track that
I'm on in addition to cochlearimplant research.
Dr. Douglas L. Beck (03:10):
Yeah, and this is a huge question for all
of science, because early on nowI'm going to tell you my
understanding.
But I am not a neuroscientistyou are, so please absolutely
correct me.
I read in a couple of differentpsychology books, in particular
the third one by Dan Levitin,where he talks about when humans
(03:33):
are born.
You know, all senses are activeand everything comes in light
and sound and tactile and smells.
And then for the first fewweeks, months, maybe a year or
two, we're actually pruning awaythose things to get sensory
lines established such thatsound is only going into the ear
and through the eighth nerve,vision is only going in through
the optic nerve and beingprocessed in the occipital lobe,
(03:54):
tactile etc.
Is that correct?
We spend a lot of that energyearly on pruning out sensory
information so we getline-labeled results, meaning
vision is to the optic nerve,hearing is to the auditory nerve
.
Dr. Brandon Paul (04:08):
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 inthe eyes and the apparatus that
we have in the ears, thecortical regions, the brain
regions themselves are the onesthat we might think of as being
tabula rasa.
Dr. Douglas L. Beck (04:23):
Yes, blank slates yeah.
Dr. Brandon Paul (04:25):
Right, and so the idea of synaptic and
neuronal pruning that happensearly in development is more
concerned with sort of thecortical architecture that is
plugged into the peripheralnerves from the eyes, the ears,
the skin and so forth.
Dr. Douglas L. Beck (04:39):
So let's talk about what happens as
somebody loses more and morehearing.
They're getting less and lesssensory input.
And then let's talk about whathappens if that person were to
receive a cochlear implant.
Dr. Brandon Paul (04:51):
Certainly, there seems to be a number of
different ways that the brainchanges after a hearing loss or
any sort of sensory loss.
A few of the more notablethings that can happen are, of
course, you reduce sort of flowof information from the ear to
the brain and as a result ofthis lack of information flow,
there can be a number of thingsthat happen.
One of the more notable thingsthat happens is neurons that
(05:14):
have lost their connection tothe ear can become hyperactive.
Neurons like to have a setamount of input.
They like the input that theyget, and when they don't get
that input, they may changetheir internal structure or they
change their connections withother neurons so they can
maintain the amount of inputthat they're used to.
Dr. Douglas L. Beck (05:31):
And that is essentially sensory recruitment
, is it not?
Dr. Brandon Paul (05:34):
Yeah, a form of sensory recruitment, and this
happens in many ways.
This could be an increase injust a spontaneous activity of
neurons.
Dr. Douglas L. Beck (05:41):
Yeah, with no stimuli, just trying to
achieve stimulation.
Dr. Brandon Paul (05:45):
Exactly, or they have larger responses to
any sort of incoming stimulicoming from the damaged sense.
So if a sound comes into an earwith hearing loss, then some
neurons might have an elevatedresponse to this and because
lower level neurons, let's sayat the auditory nerve, aren't
giving as strong of a signal.
The third way that this mayhappen is that neurons that have
(06:05):
lost their connection towhatever sense may become more
synchronously active, and thatis actually a key part to the
hyperactivity puzzle that we'retrying to figure out in brain
plasticity after hearing loss,where it's not just that you
have increased in spontaneousrates or stronger responses to
stimulation, it's also a matterof how well they synchronize
(06:28):
with other neurons too.
So we see increased neuralsynchrony between neurons that
may have lost their connectionto the ear.
All of this to me sounds likehow each individual neuron might
be trying to maintain theamount of input that it gets,
whether that's from a differentneuron, whether it's responding
to weak signals coming in fromthe periphery, or whether it's
(06:49):
having stronger excuse me orhaving more spontaneous firing
rates or spontaneous activitythat happened in the nervous
system.
Dr. Douglas L. Beck (06:56):
Now I know it's off topic, but what you
just said is kind of fascinatingand I wonder how that feeds
into the perception of tinnitus.
Dr. Brandon Paul (07:04):
Yeah, that's a separate side topic, and so
there's a strong line ofresearch that looks at whether
one of these types or flavors ofhyperactivity may be related to
the tinnitus correlate.
A lot of people have foundcorrelations between tinnitus
and hyperactivity in theauditory system.
They see humans and animalmodels of tinnitus and as well,
(07:26):
uh, how these neurons mightrespond to being plugged back
into the ear.
Dr. Douglas L. Beck (07:31):
Let's say a cochlear implant.
Dr. Brandon Paul (07:33):
Does that bring down the hyperactivity now
that we've restored someafferent or input coming from
the ear and that that could betheoretically a hearing aid.
Dr. Douglas L. Beck (07:42):
that could be a cochlear implant, assistive
device, over the counter device, anything that is now
stimulating that auditory nerve.
Right, correct, okay, so wehave these effects and these are
essentially afferent effects.
Right, and then what happens ifwe were to take that auditory
nerve which is no longer, let'ssay, the outer hair cells, the
(08:04):
inner hair cells, no longerfiring, but there's still a
synaptic connection to theeighth nerve?
So what would happen if you puta cochlear implant in many of
these ears?
Dr. Brandon Paul (08:14):
So just to understand your question, is it
about what happens to theneurons that are hyperactive if
you plug them back into, let'ssay, if you reafferent them?
Yes, exactly.
A number of things could happen.
It depends on what the state ofthat neuron might be, and now
I'm starting to get into moretheoretical waters rather than
having harder evidence for this.
So maybe a little bit ofspeculation here.
But some neurons might maintainhyperactivity.
(08:36):
They may not respond to thatreaffirmation.
Other neurons may do that Right, and so there's, there may be
some sort of reorganization thathappens when you restore the
connection to the ear.
Part of that has to deal withthat.
Even those, these technologieslike cochlear implants and
hearing aids are wonderful.
It's not a perfect restorationof the auditory system.
There's still some sort ofissues with the type of
(08:59):
information coming in iffrequency selectivity is a
little bit lower in hearing aidsand you don't really have much
frequency selectivity incochlear implants.
So there's still, even thoughit's hearing restoration, it's
partial hearing restoration andfor that reason some neurons
might come back to how theytypically operate.
Some neurons might maintainhyperactivity.
Some neurons may search forother inputs from other senses,
(09:20):
which is a main topic that Ithink that we'll get to whether
some neurons might startresponding to vision or might
start responding to our tactileor our touch system.
Dr. Douglas L. Beck (09:30):
So this is so interesting because, in my
mind, the first time I reallygave this a lot of thought was
the paper on cross-modalactivity by Hannah Glick and Anu
Sharma.
I want to say that was aboutseven or eight years ago and
here's my interpretation of whatthey said.
So as people develop more andmore hearing loss, their
auditory brainstem responsebecame less and less because the
(09:53):
ear was transmitting less andless information to the brain.
Interestingly, they noticedthat as that was happening, the
visual evoked potential wasbecoming larger and larger.
So I think this talks to thecross-modal shift that you're
addressing.
And then the most interestingfactor to me was that after they
fitted the patients withappropriately fitted
(10:15):
prescription hearing aidspremium hearing aids the visual
evoked potential got smaller andsmaller and smaller, went back
to normal and the auditoryevoked potential became larger,
larger, larger.
So, based on that, first of all, is my understanding correct on
that study?
Dr. Brandon Paul (10:30):
Yes, I think.
Yeah, the Glick and Sharmapaper from 2020,.
Yeah, a new Sharma strip inColorado.
She's done a number of reallygreat research studies on what
we would consider cross-modalplasticity in partial hearing
loss or age-related hearing loss, and the main finding is with
more hearing loss, then you havelarger or earlier visual evoked
potentials.
(10:50):
is with more hearing loss.
Then you have larger or earliervisual evoked potentials.
So you flash an image on thescreen that's maybe like a
low-level checkerboard or somesort of concentric circles or
something like this, and thenyou see the brain response to
the flash of that image is muchlarger or faster.
And then after hearing aid use,then you sort of reverse this,
and so it seems like thiscross-modal plasticity is a
reversible process which isastonishing really, absolutely.
(11:13):
It just speaks to theremarkable ability of the
nervous system to adapt to itssensory experiences, or its
sensory abilities.
Dr. Douglas L. Beck (11:18):
Yeah, because we used to say, you know
, when I was working on mymaster's, oh gosh, there were
still some little dinosaursaround.
But when I was doing that work,what we used to say, you know,
was with neural systems it wasuse it or lose it, same as
motoric systems, you know.
And if you didn't exercisethose neurons and you didn't
exercise those muscles, theywould fade away.
(11:40):
And what we're learning now isthat neuroplasticity is
reversible in some situations,in some pathways.
Dr. Brandon Paul (11:48):
And an interesting finding from the
study that you had mentioned,from Hannah Glick and Anu Sharma
.
We actually have a paper that'sabout to be pre-printed that
sort of corroborates thosefindings.
The work I'm doing at TorontoMetropolitan University is more
on age-related hearing losscompared to the work at
Sunnybrook Hospital in Toronto,which is more on cochlear
implant users.
Sure, as the question that weopened with which was does this
(12:10):
neuroplasticity happen in latelife, in aging, in older adults?
And it seems to be yes.
Dr. Douglas L. Beck (12:20):
That is the answer to that.
Both our group and AnushaArman's group have found similar
results.
Yeah, and I suspect that inolder adults I say that as an
older adult it takes a lot moreeffort to build muscle, effort
to build muscle.
Dr. Brandon Paul (12:27):
It takes a lot more effort to train neurons
particularly, I would guess thatefferent nervous system is very
difficult to challenge, verydifficult to test the efferent
nervous system.
We don't know a lot aboutneuroplasticity in those
descending pathways, and so thatis really an open question for
us researchers to address in thefuture.
Dr. Douglas L. Beck (12:48):
In some research papers.
What I've noticed is that ashearing degrades over time,
certainly other parts of thebrain will try to take over the
superior temporal lobe, orBrodmann area 4142, or Heschel's
gyrus, any of that it's allpretty much the same.
But as we lose hearing, as welose sensory input you mentioned
that vision might take overthat.
(13:10):
What I always heard early onwas that it was somatosensory
that would take over thatsuperior temporal lobe.
What is the currentunderstanding on that?
Dr. Brandon Paul (13:19):
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 ortotal deafness this happens
usually in congenital cases, soearly in life or at birth the
old prevailing view was that thedeafferented cortex and by that
(13:40):
I mean, let's say, if it'sauditory cortex in cases of
deafness that this might becomea battleground for other senses
Like oh, these neurons are nolonger getting input from the
ear and even parietal could takesome of it.
It could be remapped to vision,it could be remapped to touch.
So it turns out that's probablyan inaccurate view on what is
actually happening and usuallywe think about historically,
(14:00):
maybe neurons and auditorycortex being involved in
auditory processes and neurons.
Dr. Douglas L. Beck (14:05):
Yeah, exactly.
Dr. Brandon Paul (14:06):
Vice versa or similarly.
But we really need to thinkabout how some of the
connections actually exist inthose regions and mostly what we
should think about is thatthose brain areas are
essentially, or especially, onesthat are not in the core.
Regions like the auditory core,the visual core, are
multisensory, and what I mean bythat is cortical auditory
regions that are not in primaryauditory cortex, but we might
(14:29):
call secondary or non-primaryregions, receive a lot of inputs
from non-auditory sources likethe visual system.
Dr. Douglas L. Beck (14:35):
Yeah, sure.
Dr. Brandon Paul (14:40):
And so there's already pre-existing inputs to
those neurons from touch andfrom vision, but they're masked
or covered up because theauditory information that's
coming in is what those neuronsare most strongly responding to.
When you lose your auditoryinput now, those weak inputs can
now start responding to visionor touch.
And this is more probablyaccurate of what this sort of
(15:03):
cross-modal plasticity might be.
And it's a dynamic and fluidprocess.
It's not necessarily this largebattleground where neurons can
completely change their function.
They change their computationalability.
It's more about theup-regulation and
down-regulation of their inputs.
Dr. Douglas L. Beck (15:20):
And does most of this occur in the
thalamus, or am I way off base?
Dr. Brandon Paul (15:24):
There's currently research that's sort
of debating whether these sortof changes in the drive to these
neurons whether visual auditoryhappens through thalamocortical
pathway, so coming from thethalamus to the cortex, or
whether it's corticocortical, sofrom auditory cortex to visual
cortex or vice versa.
There probably is contributionsfrom both.
And the last thing I would liketo mention is that there's
(15:47):
probably some sort of top-downcognitive involvement as a part
of this driving what neurons areresponding to which sense, and
so it's not just a purelysensory phenomenon but it may
have the goals of the individual, whether that's visual or
auditory.
Dr. Douglas L. Beck (16:02):
All right, and I'm with you on all of that.
Let me ask you a question then.
Supposing that you haveuntreated vision loss, what
happens to the optic nerve andthe occipital lobe?
Dr. Brandon Paul (16:13):
The optic nerve itself.
I'm not a vision scientist, sothis is just from my general
knowledge from reading.
Similar to the auditory system,the visual system will
upregulate auditory behaviorsupon situations of blindness or
partial vision loss.
Dr. Douglas L. Beck (16:27):
Into the visual system.
That's correct.
Dr. Brandon Paul (16:33):
Yeah, non-primary regions, where the
regions that sort of have bothvisual and auditory interactions
, are the ones where there's alot of this give and take of
what input is stronger, whatinput is weaker.
Dr. Douglas L. Beck (16:44):
So what I'd like to ask you.
I want to go specifically nowto issues in cognition, because
your paper I actually saw thisonline and that's why I
contacted you it was in Canadianaudiologists and it was to the
brain and back the role ofvisual neuroplasticity in
cochlear implant users' speechoutcomes.
(17:04):
So we've got that.
But in there, within that paper, you talked a little bit about
cognitive effects of cochlearimplant and I think we've known
for, I want to say, eight or 10years that people who get
cochlear implants do improvetheir cognitive ability.
Can you address that for me?
Dr. Brandon Paul (17:22):
Yeah, and this is the research that we had
done with cochlear implants andsort of cognitive ability was
more along the lines ofselective attention and working
memory.
But as far as long-termcognitive changes are concerned,
my understanding is that, yes,we know that there are maybe
effects or alterations tocertain cognitive abilities with
hearing loss, and some of thosemight be remedied after
(17:43):
cochlear implantation andhearing aid use, specifically,
with respect, most acutely Ishould say, with things like
working memory and attentionwhile somebody's listening to
speech, especially in noisyenvironments.
But open question still, andthere's some evidence to suggest
that maybe long-term memorycould be affected by hearing
(18:04):
loss that could be remedied byusing hearing aids or cochlear
implants.
The effects of these things arestill debated, to which
cognitive functions and whetheror not there are truly
neuroprotective effects ofhearing aid or cochlear implant
use still are being worked out.
But there's still we have toacknowledge the preliminary
evidence that suggests there aredefinitely some benefits.
Dr. Douglas L. Beck (18:22):
Yeah, I think that's clear.
And even in the dual sensoryloss literature I read recently
and this is a paper I think cameout in 2025, probably about two
or three weeks ago and theauthors were saying that if you
have visual loss, you knowyou're at a higher risk for
cognitive decline.
If you have auditoryattenuation degradation, you're
(18:42):
at risk for cognitive decline.
If you have both untreatedvision, untreated hearing,
you're at eight times the riskfor 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 Ican ask you this question.
(19:06):
My understanding is, as hearingdegrades over time, the brain is
getting less and less auditoryinformation.
The information it gets islesser in loudness.
Of course, it's missingspectral components.
It's missing spectralcomponents, it's missing timing,
because the timing is screwedup by the sensory neural loss.
We have all sorts ofdegradation going on and the
bits that are coming through nowbecomes the new signals that
(19:28):
the brain has, and the brain,because it is plastic, starts to
accept that mushy signal as theessence of normal and then it
changes as a result of that.
What do you think about that?
Dr. Brandon Paul (19:42):
Yeah, I would say that's a good
characterization of it.
Through someone's earlier partsof their life, let's say when
their sensory abilities are morenormal, they've developed these
sets of experiences that formtemplates that whenever somebody
is listening to somebody speak,they have some knowledge about
language, they have someknowledge about how the speech
(20:03):
sounds should appear.
There's a lot of variation inhow those speech sounds might
appear, but we have a templateof what these speech sounds
might be, exactly A process ofmatching whatever comes from the
ear to those stored templates.
Now, the templates are usuallymaintained by a consistent
matching of the sensory input towhatever we have in the brain,
(20:25):
and if the sensory abilitiesdecline with age or a number of
other factors that we're awareof, then it becomes harder and
harder or more difficult tomatch these sensory inputs to
those stored templates.
But it's still possible andit's still it is possible to get
used to that, because you mayhook on to useful cues or parts
(20:47):
of speech that you know you havemaybe a good template for and
you can maybe use heuristics I'mpaying attention to this
prosodic element or I'm payingattention to the syllabic rate
or something like that in orderto achieve this template
matching procedure.
But the question is does therebecome a point where there's so
(21:07):
much reliance on the internaltemplates because the input
signal is so degraded that howdoes this change cognition,
which seems to be your question,exactly right.
Yes, you said it much betterthan I did, but that's exactly
right, no, problem the issuebecomes is that there's a lot
more opportunity to mishearinput or signals or speech
coming in from the peripherybecause you're so reliant on
(21:29):
what that template might be.
And not only are theresometimes template mismatches
that lead to errors inperception, is that your
confidence in what you'rehearing is also pretty high.
It's like no, I didn't mishearyou.
It's like I know what I believeI heard, because there's a lot
more reliance on the template,the stored knowledge, rather
than paying attention to thesensory input coming in.
(21:49):
And if it's the case that you'remore relying on your internal
model of what this languagemight be and you're not getting
reinforcement for that modelfrom the periphery, from the
environment, from the externalworld, then this can open up
opportunities for, maybe,alterations in cognition.
Maybe it's going to impact yoursocial communication dynamics
(22:11):
where it's harder to maintainsocial bonds.
Maybe, if you're trying toachieve some sort of goal in
society going to the bank, goingto the grocery store and so
forth the sort of dynamicinteractions that you need to
have there using your languagesystem become more difficult,
and so that puts strain onsocial relationships, which puts
further strain on cognitiveability, major feedback loop
(22:33):
that you get stuck in and, as aresult, then this could degrade
or decline cognition.
That's the theory, of course,rather than having hard evidence
for this, but this seems to bea way that you can put together
the available research in orderto understand, maybe, how
cognition changes as a result ofdegraded hearing, when we're
specifically talking aboutspeech and language.
Dr. Douglas L. Beck (22:52):
That's fantastic, all right.
Well, dr Paul, you've been verygenerous with your time.
I appreciate it so much.
I think your explanations makevery difficult subjects much
more clear, and I appreciatethat.
Thank you so much for joiningus.
Dr. Brandon Paul (23:05):
Thanks for having me, doug, I really
appreciate it, and thanks to allyour listeners for tuning in.
Dr. Douglas L. Beck (23:10):
I appreciate it, thank you.
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