>> Eric Horvitz: We're honored to have Dr. Richard Salvi here today. There's a great deal of interest among people interested in problem solving and machine learning and automation, machine intelligence, in fact, sometimes primordial motivation coming from how the brain works, what's going on with the brain.
It's rare to see interesting work going on that tries to take something about the subjective world and really bringing to the quantitative objective space. And Dr. Richard Salvi has been working in that realm on sensory motor circuits in the brain and links between the two. In fact, work on multimodal sensory processes in the brain.
Using as a window into some of this work, the common phenomenon that many people grapple with daily or experience, notions of hearing loss and tinnitus as one dimension and perspective on getting at some of these deeper questions.
Dr. Salvi is professor in the Department of Communicative Disorders and Sciences at the
University at Buffalo, it's the University of New York at Buffalo, and Director of the Center of
Hearing and Deafness. He did his Ph.D. work at Syracuse in experimental psychology and postdoc work at Upstate Medical Center in Syracuse.
He's written some really fabulous articles, and that's where I first recognized his work, in some of his writings on multimodality in brain probe through the acoustical system, plus plus.
So let me introduce Dr. Salvi who will be speaking today on Modeling Sensory and Motor
Circuits in the Brain: New Insights From Hearing Loss and Tinnitus.
>> Dr. Richard Salvi: Thank you, Eric. This is a little bit different type of talk that I've normally done. Usually the audience I have is strictly -- has an auditory background and we usually focus on the auditory system. But what I've tried to do today is bring in some of the work that's done on other sensory systems and some of the changes go on there.
So all of you probably recognize this famous painting that's been stolen several time by Edvard
Munch. It's basically a picture of a guy that looks like he might have tinnitus, this ringing in your ears, and it really is a very sort of strange looking picture.
The picture on the right over here is actually a window into looking into the brain of living human subjects. This happens to be my brain, and it was this fMRI image taken at Buffalo about a couple years ago, and I'm listening to a passage from Sherlock Holmes. And you can see the sites in the brain where there's a significant change in blood flow activity.
So we're going to use some of these images techniques here to actually study a phenomenon called tinnitus. Probably about 20 or 30 years ago, if you are a researcher working in auditory neuroscience, this was considered a really terrible area to go into because there were no tools to study it. And over the last 20 years the imaging technology combined with animal models that have been developed have actually sort of revolutionized the work into this.
You can think of some of this work on tinnitus as being akin to things like looking at schizophrenia. These are basically internal states, depression. And what we want to do is look at these phantom auditory sensations that originate in the brain.

So what I'm going to do today is I'm going to give you a quick view of the overview of the sensory and motor cortex, because these different areas of the brain converge and interact with one another.
And then I'm going to tell you a little bit about the central auditory pathway. Some of you may not be familiar with that. And then we're going to get into the phantom sound of tinnitus, the human and financial costs that are associated with that. And then finally we'll get into some of the research that's on brain images with a technique that I use, positron emission tomography, which leads us into the area of cortical plasticity and reorganization.
And then in subsequent years we've started to work on animal models that we could use to study tinnitus at a more cellular and molecular level. In addition to that, we've moved into a completely different area of research recently on the hippocampus and memory. Many of the people that have tinnitus suffer from severe depression, and there's some evidence they may have memory effects. And then we'll look at some of the current and clinical treatments.
So I apologize if this is too basic and simple, but I thought I would quickly review the human auditory -- or the cortex over here, not the auditory, the whole core text in general.
You can see that the human brain is basically -- consists of all these sulci, these grooves, and the gyri. And there's some major landmarks over here. This is the anterior part of the brain. Your eyes would be located under here. This is the posterior part of the brain. We're missing the cerebellum from this slide over here. And there's a gyrus over here called the precentral gyrus, and then we have lateral sulcus over here. And these basically are major landmarks for looking at the brain in some of the sensory areas over here.
So this is really a cartoon from a basic neuroanatomy book that lays out some of the important structures over here. This is the somatosensory cortex. Somatosensory cortex is where we see our sense of touch and feeling, pain. And this is -- basically lies on a strip -- the precentral gyrus -- post central gyrus over here and basically includes Brodmann areas 3, 1, and2 plus some association areas are right behind it over here. So this is the major sensory area for our sense of touch.
And this is a typical cartoon that you'd see in an introductory psychology book showing the mapping of our body surface onto the somatosensory cortex. Our feet are located up near midline at the top over here. As you come down you can see the hand. Huge representation of the face. And then the tongue and pharynx over here.
And so I draw your attention to this part because this is actually very close to the auditory pathway. So you can see how much landscape or territory is occupied by different parts of our body's surface. Our face and our upper extremities occupy a lot of territory.
This basically is the primary motor cortex where the motor outputs come. These are in the frontal area, Brodmann areas 4 over here, and you can see this primary motor area over here.
Again, the representation, our feet are located at the midline, the brain, as you go over you can see the hand, the huge representation, and then as you march down you can see the face over here and the pharynx down in this area. So these are areas that are activated, the motor circuits that are activated when we basically perform some maneuver.

Our sense of vision is in the visual cortex located at the occipital pole back over here. Here we have to look at sort of the midline structures here because the primary visual cortex is located near the midline in area 17 near the calcarine fissure. And so the [inaudible] pole where we see a lot of our acute vision, color vision, is basically located at the extreme back over here. This is a side view of the brain. You can barely see the visual cortex.
And finally we're going to take you to the area that I've been most interested in, the auditory core text, which actually turns out to be relatively small compared to the other structures I just showed you. The auditory cortex is located down over here, areas 41 and 42, this purple area.
And surrounding it is Brodmann areas 42. This area is basically an auditory association cortex.
And you really can't see this structure unless you take the temporal lobe over here and you sort look at the superior surface. So this is kind of on an infolding on the brain over here. And if you fold the brain open and kind of dissect it away, you can see areas 41 and 42.
So most of these pathways are crossed. By that I mean the somatosensory pathways, if you touch the left leg, basically that's represented largely on the right side of the brain. The same with the motor cortex. And the same with the auditory cortex. The most strongest sounds are evoked by simulation to the opposite ear.
So let's take a look at the auditory pathway and see specifically -- I don't know if many of you have thought about this, but what are the different parts of it. So we have the peripheral part of the auditory system where sounds come in. We have the collection device over here, the external ear, which is a sound-gather device, terminates with the eardrum. We have a space over here called the middle air space, and basically this is a device for getting sound from the eardrum into the fluid-filled cavities of the inner ear.
And the real nuts and bolts for hearing actually take place in the inner ear over in this particular region over here. Most of the causes of deafness actually originate right in this particular area.
So let's take the spiral-shaped organ of Corti that's encased in the cochlea over here. You can see the stapes. This is the smallest bone in the body. It plugs into these fluid-filled spaces over here.
And what we're doing over here is we're taking in -- taking a cross-section through this tube.
This tube basically has got three fluid-filled compartments: scala tympani, scala media, and scala vestibuli. And on this shelf of tissue that runs from the internal bony core to the lateral wall over here is where all the sensory cells we're hearing take -- are located.
These sensory cells basically act much like a microphone. They convert sound into neural activity. And so they're essential for hearing. If you go deaf, these are the cells that basically are lost or damaged. And we'll look at sort of this in more detail.
But one of the things that the inner ear does for us is it basically acts like a device that takes the different sound frequencies and analyzes them and distributes them to different locations.
So as the eardrum vibrates it creates a vibration of this basilar member over here. This happens to be a high-frequency vibration. And you can see the mechanical activity occurring over here.
If we were to lower the tone to a very low frequency, this bulge over here would be translated up to the apical or top end of the cochlea. So you can think of the inner ear as pretty much like a piano keyboard where the sounds are distributed in different ways. Hi frequencies would be

located down here. Low frequencies would be located up at the apex. So we have this nice tonotopic observation.
And you see this throughout the entire auditory pathway, from the cochlea all the way up to the auditory cortex, this distribution of sound, frequencies into different locations.
I mentioned something about the sensory cells for hearing. These sensory cells, if you were to look at the surface of the organ or Corti, contain these two types of cells: outer hair cells and inner hair cells. And these cells are basically responsible for converting sound into neural activity. And they do so by some mechano-transducers that are located in the stereocilia bundles over here.
These cells are really organized in really a very precise geometric relationship. You see nice three rows of outer hair cells and you see a row -- a single row of inner hair cells. And this strip of tissue goes all the way from the base of the cochlea all the way up to the apex. And the precision by which the inner ear is produced and generated is really quite remarkable.
So what happens when we get a hearing loss, when we get old or we take an ototoxic drug.
So this is actually a picture from my lab. It shows an inner ear of a young postnatal day three rat.
We've labeled the stereocilia, the hair cells, with a dye, phalloidin, that basically binds to the stereocilia over here. You can see them in green. And you can see the row of inner hair cells.
And then we have an antibody that labels the neurons. These are the cell bodies that form the auditory nerve, the eighth cranial nerve, and these are the fibers that go out and communicate with the sensory hair cells.
So sound is encoded over here, converted into neural activity. It's transmitted down these spiral ganglion neurons out of the auditory nerve and brought into the brain and then processed and sent to the central nervous system.
>>: [inaudible] 20 years ago the theory about tinnitus was that it was caused by other hair cells
[inaudible]. Has it changed much since then?
>> Dr. Richard Salvi: Yes. Everything has changed. But I'll show you some of the data why that basically -- that doesn't hold much weight.
There may be some forms of tinnitus that could be generated by outer hair cell motility, but we think the vast majority of the cases, really the tinnitus is generated in your brain, not in your ear.
And I'll show you the data that supports that.
So here we've treated an inner ear with a drug, gentamicin. This is an antibiotic. If you go in for surgery, they usually give you a day's course of this. And it doesn't actually cause much damage.
But if you take it for a week or ten days, it will actually destroy the sensory hair cells. So this is one of the ways you can damage the cells in the inner ears, taking these ototoxic drugs. Some of the anticancer drugs, like cisplatin, are also toxic to the hair cell.
So this is typically what happens when you get a hearing loss. I would say 90 to 95 percent of the people walking around with hearing loss, it's due to this type of damage.

Now I'm going to change gears on you. I sort of laid the landscape out for the anatomy of the brain and the inner ear. What I'd like to do is talk to you about this phantom auditory sensation called tinnitus, who gets it, and what's are the demographics for this.
So if you do a survey of the people that have tinnitus at one time or another, it looks like about
12 to 14 percent is a reasonable number of people. I'm sure many of you have gone out and hit a nail with a hammer and you get a transient tinnitus and then it goes away, usually a day later. If you're a musician, you played the band a little bit too long or too loud, this is -- oftentimes you'll get transient tinnitus.
But some people get it long term. And about 1 out of 4 people actually seek medical treatment for this. And then the group that really gets the most attention are the group that have what are called severe and disabling tinnitus.
These are the people that go to the ear, nose and throat doctor repeatedly looking for a cure. And the ear, nose and throat doctors who are surgeons really don't know what to do with them and they really like to get them out of the office very quickly, because there is not much in the way of a medical cure right now.
So who's likely to get tinnitus, what are the possibilities of getting tinnitus and when would you get it. Well, one of them, there's a fancy word here for age-related hearing loss called presbycusis. This is a work -- a study that was done in France, in southern France, in
Montpellier. They just basically surveyed people that came in with tinnitus and asked them what they thought the cause of their tinnitus was.
So about 40 percent believed that it was due to just age-related hearing loss. So as you approach ages 40, 50, or so, that's typically when age-related hearing loss begins to set in. Sets in sooner for some people than for other people.
Another major cause of tinnitus is noise trauma. If you're in the military, if you're over -- work in a band, you work in a noisy factory, if you're young, this a major cause of tinnitus for younger people. And, again, this study that was done in France, about 22 percent of the people had that.
If you look at combat soldiers that are over in Afghanistan or Iraq, these are not the people that are pushing papers but rather the people that are out actually doing the fighting that are around these improvised explosive devices, about 50 percent of the combat soldiers that come back from these areas develop tinnitus.
There's another group of people that develop tinnitus, and these are people that are totally deaf.
These are people that usually are candidates for a cochlear implant, they cannot hear at all. And if you survey the people that are completely deaf, they have no sensory cells, their inner ears are probably completely destroyed, about 55 percent of them have severe or disabling tinnitus. This is a major problem for them.
>>: You say that they develop tinnitus there, so the noise trauma and the tinnitus is not coincidental [inaudible]?
>> Dr. Richard Salvi: For which group?
>>: You're saying that noise trauma is a cause of tinnitus itself. Is a coincident or is it --

>> Dr. Richard Salvi: Almost instantaneous. I don't know if any of you are shooters or hunters.
When I was a younger kid, I would do that. If you go out and take a rifle and shoot it without any hearing protectors --
>>: Temporarily, but --
>> Dr. Richard Salvi: What will happen sometimes, it will actually persist. For most people it will last for like a day or two. Because usually they get a temporary hearing loss, and the temporary hearing loss will usually resolve in three to five days. Most of it will go away. And as the hearing loss subsides, you typically get a resolution of your tinnitus.
>>: [inaudible] it's pretty easy to tie it back to the trauma that caused that originally as opposed to, say, sudden hearing loss which is [inaudible].
>> Dr. Richard Salvi: One of my colleagues developed sudden hearing loss and he went completely deaf in one ear. And he said he woke up one morning, he just couldn't hear out of one of his ears. And he said actually the most troubling part of having the sudden hearing loss, he said he had this roaring tinnitus and people would be talking to him. And he said I could barely hear what people were saying above this roar inside my head.
He actually went in and had a steroid treatment. One of his colleagues put some prednisone through the tympanic membrane. And he said almost within minutes he could feel the tinnitus and the hearing loss subside. So he actually recovered probably most of his hearing in that ear.
But for a moment it looked pretty basically devastating for him.
>>: I sympathize.
>> Dr. Richard Salvi: You sympathize.
>>: [inaudible] theory about neural symmetry in the brain explain why that will happen?
>> Dr. Richard Salvi: Why the prednisone would work? Yeah, I think one of the ways I think it works is the prednisone is basically resolving the hearing loss. So if you get your hearing back, what will happen is neural activity will start flowing from the ear into the brain again.
So one of the ideas that I have, I think it's sort of my view of the world, is that tinnitus gets going because what happens, you damage the inner ear and you stop the flow of neural activity going from the ear to the brain. And when you do that the brain basically tries to compensate sometimes in ways that are completely unproductive.
So I'm going to give you a number over here. Most of the people think there's no cost associated to tinnitus, a financial cost. I'm going to give you a number that comes from the VA health care system.
So if you're a veteran and you develop tinnitus, you can go in and get compensation for it. I don't know the amounts. They're not very much. Maybe $70 a month times 12 months a year.
But then you have a lot of veterans over here.

So this was compiled by the American Tinnitus Association, some costs that the VA is paying.
So in 2009 the VA health care system paid their veterans $1 billion for having tinnitus.
Now, if we had to pay every citizen in the U.S. for having tinnitus, this number would be substantially higher. But this is the amount the government spends every year to pay these veterans. This is the amount of money that's spent on tinnitus research, $10 million by all the federal and private sources.
>>: [inaudible] the increase -- what percentage of that 1 billion is due to the Iraq War itself?
>> Dr. Richard Salvi: Actually, we don't have any breakdown of that. It's probably a decent chunk, because I told you about 50 percent of the combat people that came back from Iraq have that. Whether they enter the VA health care system immediately or do so later in their careers is really unclear to me right now. But it really is a stunning number over here. I was just shocked by how much money is being spent on it.
Now I'm going to give you the human costs of this. I don't know if any of you have experienced this. This was a Buffalo businessman that I worked with. He actually participated in one of our research studies. And this is what he wrote when a newspaper reporter asked him about his tinnitus. He said: I remember waking up on the morning of April 12, 1994, with a high-pitched squealing in my ear. I thought it was the microwave going off downstairs but I wasn't able to find the sound anymore. Ultimately I went into a state of depression and couldn't even work.
I've spent the last four years looking for help, but I've been told I have to live with this.
But this guy is a really successful businessman, he has a couple of small companies, he's well educated. And this basically completely ruined his life.
He has subsequently recovered, but for a time it really looked pretty devastating for him.
So I actually started working on tinnitus when I was a graduate student. I was trying to look at the neural correlates of sensory neural hearing loss. So we were making recordings from the auditory nerve. And one of the hypotheses at that time was that tinnitus was generated in the damaged ear. And you can see your local ENT doctor hear looking into the patient's ear trying to find that little band playing away in the cochlea to see if there was any activity there.
And so we did a lot of recording, along with other labs around the country, trying to record from the auditory nerve, which is the only pathway by which information can get from the ear into the brain. And we were hoping to see really an increase of neural activity coming out of the auditory nerve.
In fact, what you see when you damage the inner ear, if you damage it severely, is all the activity goes down and sometimes completely stops if there's massive damage.
So there's no evidence or very little evidence of hyperactivity from the -- coming from the ear into the brain. So there's little support for this. The spontaneous activity, there is no band sending a message to the brain.
There's even a more convincing piece of evidence for this, and these are patients that have tumors that grow on their auditory nerve. This is called an acoustic neuroma. And these neuromas can be quite large and they grow on the eighth cranial nerve. And surgically what you

would do is you could go in and you'd surgically remove it. Usually in the process of doing this, when you have a large tumor, the nerve has to be cut. So you basically disconnect the blood supply from the ear to the brain and the brain is no longer connected to the ear.
People that have this surgery, about 60 percent of them have tinnitus or tinnitus develops after they have this surgery. So no way could these people have a tinnitus generated in the inner ear.
It has to be generated centrally.
>>: I remember there's some [inaudible] acoustic emission, which is a small -- a different form of tinnitus [inaudible].
>> Dr. Richard Salvi: Yeah. You're absolutely right. There's the type of thing where you can have -- the outer hair cells in your inner ear can be spontaneously active and they can generate an electro-motile response.
>>: [inaudible] to be very [inaudible].
>> Dr. Richard Salvi: We actually were one of the people -- we published a paper in Nature showing that if you had -- we had some animals that had high levels of spontaneous activity, and you could actually see high levels of neural activity coming from the cochlea into the brain.
But the interesting thing about people that have spontaneous otoacoustic emissions, if you ask these people do they have tinnitus, most of them don't perceive it.
>>: So it's just [inaudible] level of concern.
>> Dr. Richard Salvi: What we think might be happening is it's there all the time and because it's there all the time, 24/7, the brain simply tunes it out or ignores it.
But it's a very, very small part of the population that have spontaneous otoacoustic emissions.
For those small subset of people that have that, you can actually see an increase in neural activity, at least in the animal models, going from the ear to the brain. But the people that have them, if you interrogate these people that have spontaneous emissions, they say I don't hear anything.
>>: I thought that once the levels goes high it become tinnitus [inaudible].
>> Dr. Richard Salvi: There's some clinical reports in the literature of people walking into a doctor's office -- I don't have the references right on the tip of my tongue -- where people will say -- they walk into the doctor's office and they'll say what's that sound, and you can actually put your ear up to the patient, you can hear a sound coming out of the ear. But in most cases the patients can't even hear the sounds that the ear is generating.
We had some chinchillas that had this. You could actually take the chinchilla, hold it up to you ear, and you could hear it. And it was a real signal being sent to the brain. But the people actually don't seem to be able to perceive that phantom activity, or that activity that's coming from the outer hair cell.
So if the activity goes down when you damage the ear, one of the questions you can ask yourself is what's going on in the brain. And this is how we sort of got into tinnitus research, was we had

done these studies on noise-induced hearing loss, and we had been recording the neural activity from different regions of the brain.
We put electrodes on the inner ear and recorded the compound action potential from the auditory nerve over here. We recorded from the next relay station the cochlear nucleus over here. And we recorded the -- from the midbrain structure called the inferior colliculus. And what we did over here is just played different sound intensities and we measured the level of the neural activity coming from these different centers.
So this is the day that we got before we gave the sound exposure. We had a robust response from the inner ear. The animal was noise exposed, and the activity from going from the ear to the brain was diminished. That's pretty much what you'd expect.
We looked at the next relay station, the cochlea nucleus. Again, depressed. But by the time we get up to the midbrain, we can see the hearing loss being expressed over here, but once the sound gets above threshold, it actually rises above and the neural activity exceeds the activity we got beforehand. So looked to us like the brain was becoming hyperactive after we damaged it.
So this is another study much in the same vein but instead of noise exposure we gave some animals a drug called carboplatin. It's an anticancer drug that damages the group of sensory cells in the chinchilla inner ear called the inner hair cells.
Again, we recorded from the cochlea over here. This is before we gave the drug. The red symbols show after we gave the drug we got about a 30 to 40 percent reduction. So the brain is getting 30 to 40 percent less activity. And then over here we're recording from the cortex. And the cortex, in spite of getting less input from the ear, actually is hyperactive.
Had a question back there.
>>: What it is about chinchillas in particular that makes them the right model for this?
>> Dr. Richard Salvi: We used to use them a lot. We don't use them much anymore. One of the reasons they were used is their range of hearing is almost identical to humans. They hear from about 20 to 20 kilohertz. If you go to rodents like a rat, everything shifts up an octave to an octave and a half. If you go to a mouse, it shifts maybe up almost two octaves higher. So they're not very good -- chinchillas are not very good for molecular biology either.
>>: Is the basic pathway including the basic structure of the inner ear pretty much consistent across mammals?
>> Dr. Richard Salvi: Really remarkably similar. You could -- yeah, we look at the inner ears from the different species. At the peripheral level they're quite similar. There's probably some major differences or some significant difference as when you go up and you look in the central structures.
So the take-home message from this slide over here is when you dam- -- go ahead.
>>: So is it the case that the hyperactivity occurs at a lower [inaudible] level when there's the carboplatin-induced hearing loss rather than the noise-reduced?

>> Dr. Richard Salvi: Carboplatin is a little bit different. Because when you produce these lesions in the chinchilla inner ear, if you damage just the inner hair cells, which this drug does, you actually don't get any hearing loss. The threshold for hearing doesn't change.
But what does change is it looks like the brain becomes hyperactive. And these animals, if you test them on a bunch of psychoacoustic tasks, listening tasks, they have trouble hearing a tone and noise and they also have trouble processing rapid temporal fluctuations. One of my graduate students did this for his dissertation.
I think the major take-home message over here is when you damage the inner ear you basically slow or reduce the amount of neural activity going from the ear to the brain. But what the brain does is it seems like it begins -- tries to compensate for this lack of input.
>>: So do you have any update how evidence showed that different part of hair cells, inner versus outer hair [inaudible] provide different result on this?
>> Dr. Richard Salvi: Well, there's a major difference between the roles of the inner and outer hair cells. That's kind of a story that's emerged from a whole bunch of labs. But the outer hair cells have very few synaptic connections with the brain. Only 5 percent of the neurons actually contact the outer hair cells. It's a puzzle because three quarters of these sensory cells in the inner ear are connected to outer hair cells.
So the outer hair cells have a unique property, and that is they are electro-motile. If you change the voltage on an outer hair cell, it actually will increase its length and contract and elongate.
So the conventional wisdom right now is the outer hair cells act like a motor system. They provide positive feedback in a very frequency-dependent way. But they send very little information, if any, into the brain. All of the information sent into the brain or the vast majority of it seems like it comes from the inner hair cells. So we have these two populations and they seem like they have a completely different function.
This is sort of an interesting slide and it gives us some insights into what actually might be going on in the brain to be increasing the neural activity when you have a lack of cochlear input.
What we've done over here is we record the local field potential from the auditory cortex. And then what we did is we put a drug on called bicuculline. Bicuculline is a drug that blocks
GABA-mediated inhibition.
So one of the major inhibitory neural transmitters in the brain is GABA. And this is the activity, sound-evoked activity, before we block the GABA-mediated inhibition, and this is shortly afterwards we put this blocker on.
What you can see is just tremendous increase in neural activity just by getting rid of the brain's inhibitory -- local inhibitory circuits.
Not only do you increase the sound-evoked activity, but you can also increase the spiking activity from individual neurons. This is before we gave the drug. This is the neural activity in the cortex. And afterwards you can see a huge increase in the spontaneous activity.

So one of the ways we can kind of conceptualize this problem of tinnitus is kind of like driving a car where you have two controls for driving your car. You have the cochlear activity which provides the gas and oxygen to drive the central nervous system. So if you want to hear you basically got to step on the accelerator. But you don't want to get the activity to be too high, so you have a bunch of braking systems. Glycine is one, GABA is another one.
What we think what happens when you get a hearing loss of some sort is you decrease the amount of gas going into the engine, the amount of neural activity. And what the brain does to try to compensate for that lack of activity, it takes its foot off the braking system. And so you get these increases in neural activity in the central nervous system. They probably occur at multiple levels, and this is an extremely simplistic representation of what I think is going on.
What I'd like to do now is show you the data that actually supports the notion there is a central sort of mechanism for tinnitus. So we think the tinnitus is probably generated in the central nervous system. When you damage the periphery, you get a loss of input. And what the central nervous system does is it tries to compensate for this reduced input by increasing its gain. And we think the generator for tinnitus is actually -- is in the brain and it gets going because of the lack of cochlear input.
So about in the late 1990s I did some work with a neurologist who had a PET imaging center.
PET is a way of imaging the brain. It uses a radioactive tracer. There's various types of tracers you can use: carbon, nitrogen, oxygen, fluorine. We happened to use radio-labeled water.
Radio-labeled water is used because it has a very short half-life. You can use the radio-labeled water as a surrogate marker for a blood flow in the brain. If a part of the brain is really busy, it demands more blood flow and you can sort of measure the activity by assessing kind of local blood flow in different regions.
So the subjects, we will give them radio-labeled water. This has a short half-life. You can measure about eight scans per person. And then you put them in a scanner and these -- the gamma rays that are given off when the isotope breaks down, you get two gamma rays that go off in either direction and they have this coincidence detectors on the opposite side of the brain that basically record when these gamma rays come in and they back-calculate and they determine basically where the gamma rays are emitted from. There are millions of counts and there's a lot of calculations that go on.
So the first thing we'd like do is we'd like to see where does the brain -- how does the brain respond to sound in the first place, how are sounds processed, what can you see with this PET imaging technique.
So these are some scans that were done on normal college students. We played a sound just to one ear, to the right hear. We played it at 90 dB above the normal hearing levels. And these are the areas of the brain that are activated.
So the areas in color over here are areas where we see a significant increase in blood flow to the brain. And the images on the background over here, the gray images, are basically MRI images of a human brain. This is a standard human brain over here.
So when you put a sound just into the right ear -- left and right is reversed on all these slides.
When you put a sound into the right ear, over here you see activity in the auditory cortex, on the left side in the right side. So I want you to remember that: When you put a sound in one ear,

you get activity on both the right and left auditory cortex. You get activity in another area called the left medial geniculate. This is well known to be an auditory area that feeds or delivers information into the cortex.
And then we begin to lose spatial resolution down here. We call this the lateral lemniscus. This is down in the brain stem of the midbrain. And then you get down to the brain stem down, here we can see a signal. We can also see some activity surprising in the parafloccular lobe of the cerebellum.
>>: This is activity from a single person, or are these average over all the people --
>> Dr. Richard Salvi: These are average probably across I think about eight or ten college students. If you're going to do statistic -- there's a program we use called Statistical Parametric
Mapping and you need to basically have multiple scans from multiple subjects to see areas where there are significant changes.
>>: But the images are accurate with respect to the relative [inaudible] entire rest of the brain that --
>> Dr. Richard Salvi: That's exactly right. These are the only places where you see a significant change in blood flow. So the changes in blood flow are actually not very great. They're only on the order of maybe 3 to 5 percent increases over the background activity.
So you get a scan in the resting state, when you're just sitting there, and you have another set of scans that you get when the sounds are presented, and you compare those two sets of scans and you can see exactly where the blood flow has changed.
>>: So what do you use the single count as a [inaudible] rather than the complex count where you make a [inaudible].
>> Dr. Richard Salvi: Simple minds require simple counts. No. We wanted to start off with a really -- we actually did this with about three or four different frequencies.
But you actually raise a very important question. I showed you the first picture of an fMRI scan of me listening to Sherlock Holmes. If you listen to a complex sound, you actually produce tremendous activity in the auditory cortex. If you use a very simple stimuli, the activity actually is not as great. So you get much more robust activity in the cortex, the central structures, when you use complex stimuli.
But we wanted to use simple tones because we wanted to look where the activity would activate different parts of the auditory cortex, and you can't do that with complex.
>>: But the single tone are really actually pretty loud [inaudible] the one you showed earlier.
>> Dr. Richard Salvi: Yes.
>>: So [inaudible].
>> Dr. Richard Salvi: Yeah. PET does not have very good spatial resolution. It has -- is very good if you make a trace that will bind to a specific receptor, but its spatial resolution is not as

good as fMRI. Most of the people are doing these types of studies right now are doing functional magnetic resonance imaging.
So this looks like a very peculiar sort of picture, but it's a type of tinnitus called somatic tinnitus.
And it's a type of tinnitus that you can manipulate the loudness of your tinnitus by sticking your tongue out or moving your jaw.
And when we did our imaging studies of tinnitus, initially when we were going to do it we were going to go and compare people that had tinnitus and we were going to compare them with people that didn't have tinnitus. As soon as you do that type of study, when you do between subjects experimental design, you run into problems. You have gender differences, you have age differences, you have differences in hearing abilities and all kinds of biological variability.
So one evening I went to a tinnitus support group and trying to recruit subjects for our study, and there were people in the audience, I told them about our study, and they said, Dr. Salvi, I want to tell you about my tinnitus.
One woman gets up, she says when I stick my tongue out my tinnitus gets louder. I kind of looked at her, I paused, I think my eyes rotated around in my socket in kind of disbelief. I said, you know, this just can't be possible. And a few minutes later another woman got up and she said, Dr. Salvi, when I clench my jaw my tinnitus gets quieter. Again, I sat there in disbelief.
And finally a third person got up, the Buffalo businessman that I talked to you about, and he said he could do.
Then kind of a light bulb went off in my head. I went back and told my colleague, I said, Allen, the way we're going to do this study is we're not going to compare different groups of people, we're actually going to bring these same subjects in, we're going to believe that they can modulate their tinnitus, and we'll get a scan where their tinnitus is quiet and we'll get it when it's loud.
And it --
>>: Can you hear the tinnitus when you are next to the patient?
>> Dr. Richard Salvi: Both people, no. They have what's called subjective tinnitus. They cannot hear it. Yeah.
So it turns out -- we used to think this was a very rare phenomena. But if you carefully interrogate, most people that have tinnitus, turns out that about 70 percent of the people can modulate their tinnitus, even by moving their head, thrusting their jaw out. It seems like the cranial nerves No. 5, the trigeminal nerve, plays a major role.
And in addition to this, some of the spinal nerves that come up from the upper cervical region are also areas that feed into the auditory system.
So what we had people do is not as exaggerated as this, we just had them clench their jaw while they were in the scanner. We get a resting scan before they clench their jaw, we make them do the jaw clench, this orofacial maneuver, and we wanted to measure where the tinnitus was occurring. And we also played sounds to them because we thought that they might have hyperactive nervous systems.

So this is the results from this paper that really got a lot of press when it came out. But this shows some patients that could make their tinnitus louder. There was one subject here in two pieces -- two patients who could make it quieter. And what you do is you run an analysis of covariance and you sort of ask the question what parts of the brain are changing when the person's tinnitus changes.
So here we have loudness decreases. We get a scan of the blood flow in the resting state. We expect their tinnitus to go down when they make the orofacial maneuver. So you'd expect a high level of blood flow and a lower level over here. And then we have this other comparison where we have loudness increasers, so they clench their jaw, the tinnitus gets louder than the resting state.
So this is if you had to sort of draw a little arithmetic equation. This is not exactly how it's done statistically. But this is what it would sort of look like. So we did this analysis, we found that the places in the brain that lit up were Brodmann areas 21 and 41 in the left auditory cortex over here. You can see these areas of activation on the left side of the brain. And these are horizontal sections through the brain. And you can see basically the activity here in the cortical areas over here.
But the important thing to notice, if this was a real sound beginning in the inner ear and propagating up to the brain, it ought to activate both sides of the brain, but it activated just one side of the brain. So one of the conclusions we drew from this was that tinnitus must be generated centrally rather than peripherally.
Another area that sort of showed up that was really sort of a surprise to us was this area in the left hippocampus. And we're going to come back to this later on in my talk. The left hippocampus had actually been implicated in tinnitus because it's a memory area, it's part of the limbic system, and there's a fellow by the name of Jastreboff who had a theory of tinnitus that said the reason that tinnitus becomes so debilitating is the neural activity in the auditory centers get linked into memory and emotion. And this is actually turns out I think the only piece of data at the time that actually showed you could have activity outside the auditory pathway.
We also see activity in another auditory structure called the right medial geniculate.
So these patients in addition to having a signature for tinnitus that we could detect, they look like their brains are hyperactive. And what we did is we actually played normal sounds to subjects over here. These are 2,000-hertz tones. You can see activity in both sides of the auditory cortex.
These are normal subjects over here. And then we did the exact same experiment with these people that had tinnitus. And then we compared the tinnitus brains with the brains of normal subjects.
And if the processing in these two sets of brains, the normal and the tinnitus brains, were identical, these images should show up as blank. But what you find is that the people that have tinnitus, when you played a sound to them, their brains were hyperactive. And Brodmann areas, this auditory cortex area over here, was much more active in these people that had tinnitus. Fit in actually very nicely with our animal model data showing hyperactivity in the central nervous system.
>>: But in that case do these patients have ear damage?

>> Dr. Richard Salvi: What we did is we played the sounds to these people at a frequency that was just in their normal range. They actually have a high-frequency hearing loss. All of them had a hearing loss of around 4 to 8 kilohertz. So we played these sounds. I think they were at 2 kilohertz, which was right at the boundary between their normal hearing and their abnormal hearing.
>>: So in that case the theory would have to say that conversation has to [inaudible].
>> Dr. Richard Salvi: Yeah, we do. Actually there's data that suggests that this hyperactivity spreads into other frequency regions.
Yeah, Brian.
>>: [inaudible] there is associated with tinnitus hyperacusis. I was wondering if this might be a way of explaining that.
>> Dr. Richard Salvi: I didn't really play on that when I mentioned tinnitus. This is the phantom sound. But oftentimes people come into a clinic and they say I -- in addition to having this ringing in my ears I just cannot stand to be around loud sounds. So my wife is a little bit like this. When she hears a vacuum cleaner, she just really runs away. I don't know if it's because of a cleaning phobia or hyperacusis.
But there are many people that come in and they really cannot stand loud sounds. So we had a guy that came up to get tested for his hearing and his major complaint was when the sounds got really loud, he just couldn't stand it. He just had to get out of the room.
>>: The distortion is quite high, I can say from personal experience [inaudible] it gets to a certain sound pressure level and it's very, very distorted. If you don't know that [inaudible].
>> Dr. Richard Salvi: Are you a musician?
>>: Yeah [inaudible].
>> Dr. Richard Salvi: You actually sound like the patient we tested about three weeks ago. We had this guy come up from Connecticut. He's a musician and he makes albums and stuff. And he could actually identify exactly -- before we even tested him he knew where the pitch of his tinnitus was located. He has severe hyperacusis. And he said the thing that was most troubling for him when he listened to sounds, they just sound completely distorted. He says if I'm a musician, you know, this is just going to ruin my life.
So you see this complex, the distorted-pitch hyperacusis, and tinnitus seemed like they go together. But the hyperactivity fits in very nicely with the notion of hyperacusis.
So I'm going to tell you about another weird form of tinnitus called gaze-evoked tinnitus. This is a type of tinnitus that usually develops when you take a tumor off the auditory nerve as our vestibular schwannoma. You actually get this form of tinnitus when your eyes are looking straight ahead the tinnitus is either very low level, and your eyes go to the left or to the right, the tinnitus goes up.

Now, if I had something like that and I went in to talk to my doctor, I think I'd be a little reluctant to tell him I had something like this for fear of what he would think of me.
So at the time that we did this study, if you went and looked at the scientific literature, there were probably only two or three papers that were actually done where this was reported. So we thought, jeez, how are we going to get any patients to come in that have gaze-evoked tinnitus.
So we put an ad in an acoustic neuroma newsletter, just a single notice that we were going to do this, and immediately we were flooded by e-mails from people that actually had gaze-evoked or gaze-modulated tinnitus. And we actually published a paper because we had so many people that could do this.
This actually is not our slide but this is a slide from a woman that actually appeared in the literature. She had this huge tumor on the right side over here. She was 44 years old. And this was a journal article. This woman that appeared in this journal article, she actually contacted us.
She lives in Kansas. So we put her on an airplane and we flew her out to Buffalo and we actually scanned her as well as a group of other people.
So, again, this gaze-modulated tinnitus or gaze-evoked tinnitus is very nice because you can get a scan when the tinnitus is quiet, looking straight ahead, and then you can have them move their eyes and you can see what parts of the brain light up.
So I show you data from one subject. This was a subject that had gaze-evoked tinnitus that came about from a left acoustic neuroma, and we see nice activity in an area called the angular gyrus over here. Turns out this angular gyrus lies right at the intersection of the auditory processing areas, the visual processing areas, and the somatosensory processing areas. They're right at the same area. And there's actually data in the architecture that suggests that this basically is involved in auditory processing.
So there's -- those -- last example on the gaze-evoked tinnitus, that has to be centrally mediated because these people don't have any activity coming from their auditory nerve.
Now, if you look in the literature, if you go online and say, jeez, I really want to find a cure for my tinnitus, how am I going to do this. And there are clinics around the country that will give you a shot of lidocaine. Lidocaine is what you go into get a tooth extraction. But they don't give it to you locally. What they do is nay injection this drug, the sodium channel blocker, into your -- intravenously. And if you look into the audiology literature and otolaryngology literature, that will give you a temporary cure of your tinnitus. So a lot of people go to this clinic to get cured. And it usually lasts for a short time and then goes away.
But if you read the cardiology literature, this is a drug that's often used to test for heart arrhythmias and they give it to patients. And one of the warnings is when you give lidocaine intravenously you get tinnitus.
When we did our study we were sort of naive, we only knew the upper half of the slide. So it even shows you the college professors are naive and have a limited look on the world. So when we did our study, we actually took these patients and we measured the activity from the brain.
And what we did over here is we found the areas of the brain where the tinnitus changed when we gave them lidocaine.

And these are all sort of auditory association areas or primary auditory areas in the auditory cortex and around the auditory cortex. This graph over here shows you the change in blood flow that goes along with this.
So if you're a person that reported your tinnitus got quieter after you took the lidocaine or had the lidocaine injection, basically your blood flow in this region went down. If you're a patient that claimed that your tinnitus got louder after this, then your blood flow increased. So this is again a nice piece of data showing the central origin to tinnitus.
Now I'm going to show you some data from some other groups. One of my postdocs sent me this just before I was coming out here. It was done by Musacchia and Schroeder over here showing the connections to the auditory cortex over here.
And you see a lot of inputs from the somatosensory cortex, clenching your jaw. You see inputs from the visual cortex going into the auditory areas, and you see some areas from the prefrontal cortex. These could be from the areas around the supplementary motor cortex that drives some of the eye gaze.
So we see -- and these are normal animal models where people have measured the inputs that come into the auditory cortex. All of these areas are communicating with one another.
Now I'm going to show you I think a really provocative slide. This is actually done by this guy
Brian Allman that works in my lab. It was published in Proceedings of the National Academy of
Science .
What they did is they took ferrets and they mapped out the auditory cortex. So this is a ferret brain. This is the auditory cortex area over here. And the panel B over here shows you the various auditory fields in the auditory cortex. A1 is the primary auditory cortex.
And what they did with these ferrets, they deafen them, completely deafen them. They gave them a couple of ototoxic drugs, so the ferrets were completely deafened.
And after they deafen them -- a month later is when they went in -- is they would record from the auditory cortex -- remember, this is supposed to respond to auditory stimuli, right, because it's called the auditory cortex. Instead what they found is they would touch the animal on the face.
You could see all the areas of the face. These black areas are the places of the animal's body.
And when they touch these areas, they would evoke activity in the auditory cortex.
So I'm sure you heard the phrase "use it or lose it." So what happens in the auditory cortex, if you stop using it because you go completely deaf, what happens, the cortical areas get taken over by other sensory systems. So somatosensory is one that really invades this area. But the visual cortex can also invade this area over here.
And the invasion probably is not too surprising because there are already preexisting connections into these areas over here as I showed you in the previous slide.
>>: So does human also have similar [inaudible]?
>> Dr. Richard Salvi: Yes. As a matter of fact, exactly. There are patients that get what are called cochlear implants. And if you take these patients and you do a brain imaging study on

them and they are completely deaf before you do the implant, what happens is you don't get any activity when you -- or if you touch them in different parts of the body, you can get activities in the auditory cortex.
After they get the cochlear implant in the beginning you don't get much activity to sound stimulations that are coming in through the cochlear implant. But if you wait three, six, or nine months, eventually this starts responding again to auditory input.
And people that seem like they perform well on their cochlear implants are the ones where they basically get restoration of auditory inputs over here.
So you can see the dynamic characteristics of the cortex. If you don't use it, it basically gets taken over by some other sensory system.
>>: So the question is that this is for the body touch [inaudible] any data that shows when people speak a sound it's produced from vocal system that similar things happen?
>> Dr. Richard Salvi: I don't know the data right offhand. I'd probably just not say anything about that right now because nothing comes to mind right now.
So what we think happens, the tinnitus, one of the reasons it gets going, when you get the loss of cochlear inputs, basically you get this abnormal plasticity, the last slide by Allman that I showed you where you get the cortical reorganization occurring.
We think it's analogous to phantom limb pain. And we think this can begin because these circuits are already there to begin with. They just basically -- the auditory structures stop stimulating them and the other structures take over.
So what we've been interested in doing now is trying to find ways of testing tinnitus in animal models. And so we've basically developed a couple of ways of testing them. One of them we called SIP-AC. And I'll basically move ahead because I think we're going to run out of time.
So what's happening here, this animal has been trained. If there's any sound on the environment, he's not supposed to be licking for water over here. But when the sound goes off, he can go in there and he can lick. So he's been trained do this. I didn't go into all the details.
>> Eric Horvitz: [inaudible] the time.
>> Dr. Richard Salvi: Pardon?
>> Eric Horvitz: We have till noon.
>> Dr. Richard Salvi: Okay.
>> Eric Horvitz: Yeah.
>> Dr. Richard Salvi: So, anyhow, they're trained to lick for water when it's quiet out. And if there's any sound, don't lick for water.

And the way we do this is we have this technique called scheduled-induced polydipsia.
Polydipsia is when you drink and you're not thirsty. Kind of like eating potato chips at -- when you're watching TV and pretty soon you're having beer, glass of wine, or soda.
Anyhow, you can use this technique. It works very nicely. And you can train animals up. So one of the ways you can induce tinnitus very reliably in animal models and in humans is to give them a high dose of aspirin.
So the conventional treatment for people that had arthritis 20 years ago is you take a high dose of aspirin. And the way they would triturate in on the dose is you keep escalating the dose of aspirin until your ears starting ringing, and then you'd back off the dose a little bit. So you could actually find papers on how you get the right dose for treating rheumatoid arthritis. So you can give animals high doses of aspirin and you can see them develop tinnitus.
So over here the blue lines are when they're licking in quiet. You can see they lick a lot when it's in quiet. If there's any sound on, there's no licking whatsoever. And this is baseline conditions.
We give the animal injection of saline, you just get the same thing.
But if you give them a high dose of aspirin, 350 milligrams, they completely stop licking. You stop giving the drug, the licking comes back. You give them 150 milligrams of the drug, they stop licking and then they recover. You give them 50 milligrams, this drug dose no longer has any effect.
So this is data from a single animal showing how you can measure tinnitus. So the animal, when he hears the phantom sound of tinnitus over here, he stops licking because he has tinnitus. It's actually a very clever way of doing this.
And you can do drug dose response studies. These are licks in quiet, the black lines, baseline, saline, a low dose of -- let's let guys lick, and then as you start escalating the dose, once you get up to about 150 to 300 milligrams per kilogram, the animals looked like they reliably get tinnitus over here.
So now you can begin to test drugs to treat tinnitus, because that's what most tinnitus patients want, they'll call me up and they'll say what can I do to take my tinnitus.
So there's a drug called memantine. It's an NMDA antagonist actually used to treat Alzheimer's disease. It blocks the NMDA receptor. We have this drug company in Denmark, they wanted to test this drug out. These are controls, saline, memantine alone, these two lines, so the saline and the memantine didn't do anything to the animals licking in quiet.
We give the animal sodium salicylate, the guy stops drinking. And then we give him salicylate plus memantine. It looks like they're getting a little bit better. So we escalated the dose to 3 milligrams per kilogram of memantine and it actually didn't go up.
So it looks like this drug might actually have some partial benefit, but it never makes the tinnitus go away completely.
One reason for mentioning this, there's a drug company in Germany right now called Merz
Pharmaceutical. They're actually running a clinical trial with a memantine derivative trying to

see if it suppresses tinnitus. And we actually have a clinician in Buffalo that's actually doing part of the clinical trial.
Now, another drug that's been thought to be a treatment for tinnitus is a drug called scopolamine.
It's an anticholinergic. You take it when you have motion sickness. This basically shows you what the drug does alone.
This is licks in quite, baseline, saline. If you give them 2 milligrams per kilogram of scopolamine, it actually disrupts their behavior. So you can't really use this drug because it will ruin your measurements. So you can use one milligram per kilogram.
So over here we induce tinnitus with sodium salicylate. You can see the drop down over here.
We give scopolamine alone, has no negative affects, and you give scopolamine plus sodium salicylate and you get some partial reversal of the tinnitus. But it doesn't bring it back all the way back to normal. So this might have some merit, but it doesn't seem to completely block it.
So the company we're working with in Denmark called NeuroSearch, they have a potassium channel modulator. And the reason they wanted to use this is they had some insights about how this potassium channel modulator could work.
They know it acts on a particular type of potassium channels that are found in the ear. These are called Kv7.2 to 7.4. And you see a lot of these channels expressed in the ear and the brain. They also work on these Kv7.1 channels as well as these BK channels over here. And this drug works spectacularly well in our head. It's an experimental drug; it's not used clinically.
Over here you can see the licks in quiet and baseline, saline, and then we give the drug alone.
It's called R-Maxipost [phonetic] and doesn't do anything negative. You give 10 milligrams and you get a little bit of a negative effect.
And then over here what you can do is you give tinnitus and you get a big reduction -- you get a big reduction in licks in quiet, so we think the animals have tinnitus over here, and then as you escalate the dose of R-Maxipost, you drive this right back up into the normal range. So we really like this drug because it really works in a nice dose-dependant manner.
>>: When you say the motivation is because of testing channels in the ear [inaudible]?
>> Dr. Richard Salvi: That was what the drug company was interested in.
>>: But by coincidence happen to have effects on the central nervous system?
>> Dr. Richard Salvi: These channels are actually -- most of these drugs are found ubiquitously.
>>: [inaudible] motivation, that's all.
>> Dr. Richard Salvi: That was their motivation for doing this. In fact, when we did the initial drug testing, we didn't even know what we were testing. They had a different name. They had
NS 1882 and 1883. So they didn't even tell us what we were testing for them, which is good.
That's fine.
>>: This combination here looked like you had the sodium salicylate in there as well.

>> Dr. Richard Salvi: Yeah. Right over here is the salicylate. You get tinnitus here.
>>: Must have caused the tinnitus.
>> Dr. Richard Salvi: Yeah. And then we want to see if we can reverse it, and we can completely reverse it.
>>: Same amount was used in all --
>> Dr. Richard Salvi: Yes.
>>: -- to give you [inaudible] tinnitus?
>> Dr. Richard Salvi: If the tinnitus wasn't going away, then we'd be down here. We'd have a flat line. But as we gave this, as we ramped up the dose of R-Maxipost, you could see the tinnitus disappearing here.
>>: Seems promising.
>> Dr. Richard Salvi: Yep, it does. Yeah.
The ways I just showed you for testing tinnitus are really labor intensive. It will take you a month to train the animals. And if you're a drug company, you'd like to have something that was a faster way of screening it.
So there's actually a screening technique that we've developed along with some other legs. It's called basically a startle reflex technique. And what you can do is if you want to elicit the startle reflex you present a loud, short tone. If I clap my hands and I come next to you, your eyes will blink. That's the human startle reflex.
Animals, basically you can put them on a little platform and we have a piezo sensor underneath.
And what you can do is you can measure the startle response.
So here we presented this short pulse, 115 dB, and you can see the startle response over here.
And we have the background noise going on at 60 dB over here.
Now, what you would look to do is modulate the startle reflex. And the way we can do that is we can take the background noise over here and we can have a prestimulus, a silent period, go on for 50 milliseconds, and you can see when the animal is here this prepulse silent interval. The thing that happens, it suppresses their startle reflex.
So this is a well-known phenomena in people that do work on things like schizophrenia. They don't use exactly the same paradigm, but something similar to that.
So here you can see the animal startling to that stimulus. He's sitting on this piezo. Every time the pulse comes on you can see the guy sort of startled to this. So there's no training involved, they just do it. So it's actually very clear. Even when he's grooming he basically startles.

So we wanted to see what would happen. We put these -- we have a gap in the noise, and the gap in the noise basically suppresses the startle response. And we want to see what happens when we induce tinnitus in these guys.
So the data I'm going to show you over here, the dark brown bars show you the data. We have a background noise located at 67 kilohertz. We have a background noise at 12 kilohertz and we test the background noise at 16 kilohertz. And over here what we're plotting is how much we can suppress the startle reflex when we put the gap in. So normally we can suppress it around 50 to 60 percent. We can suppress the reflex by putting that silent gap in there.
Now what we do is we induce tinnitus. We go back and we give them a high dose of salicylate and we repeat the measurements. You can see the inhibition of the startle response is going down, down. And when we get up to 16 kilohertz it really goes down.
So how do we interpret this data? Well, what we think is going on over here is when you have the normal gap, this gap will basically suppress the startle reflex. But if you have tinnitus and the tinnitus pitch matches the sounds that are before and after the gap, what happens, you get signature presentation of the startle reflex.
And that's exactly what happens in our animal model. It looks like this is a very nice way to measure tinnitus and it has a very high throughput. So we're actually doing some drug screening now with that technique.
Now, one other thing we'd like to do is we'd like to know what the neural signature for tinnitus is. So in order to do this we've been recording from the auditory cortex. We put these multichannel electrodes in the auditory cortex. So here's -- there's 16 recording channels and you put them into the cortex over here of an animal.
And this shows you a data you can actually record from animals while they're awake. So these little blips over here are the spike discharges, and this is the rat kind of just walking around over here. You can pick up the activity from the auditory cortex.
So what we'd like to do is see what's going on in the auditory cortex when we induce tinnitus, what's going on with the activity. So if you filter the response that comes from the electrodes you can record what's called the evoked potential or the local field potential. And you can also record the spike discharge. So we're going to look at both of these types of activity.
>>: Can you do multi [inaudible]?
>> Dr. Richard Salvi: These are multiunit. They're probably clusters of units, small clusters of units.
>>: Basically extracellular, basically.
>> Dr. Richard Salvi: They're extracellular, yeah.
So here's the sound-evoked neural activity. Here's our 8 kilohertz tone burst. We put the sound in before we give the drug. There's some activity. And look what happens when we give the salicylate. The activity in the cortex goes up. We know that this drug actually slows down the activity from the cochlea, but when you go up to the cortex, you actually get hyperactivity. So

the evoke potential goes up. And when we think we have a bunch of data, I'm not going to go into it, it looks like salicylate. If you take it at really high doses, what it does, it suppresses
GABA-mediated inhibition.
If you look at the spike discharges occur, these are what we call post-stimulus time histograms, the number of spikes that you get when the stimulus is on. You can see them over here. And this is just kind of the spontaneous activity.
After we give the salicylate, actually get an increase in the spike rate to the sound but a decrease in the spontaneous activity. We were hoping we'd see an increase in spontaneous activity, but we got just the opposite. So we're a little bit puzzled by that.
>>: So that's going to be auditory cortex area.
>> Dr. Richard Salvi: Yes.
>>: So do you do simultaneous [inaudible] somatosensory and motor [inaudible]?
>> Dr. Richard Salvi: It would be very nice. I'll have to say these are extraordinarily difficult experiments to do and we're still working on sort of developing some of the technology for that.
I'm going to skip over the rest of this over here.
So one of the symptoms that goes along with tinnitus are impairments and concentration. If you do assessment of people with tinnitus, they actually -- there's some reports in the literature of being cognitive impairment. We often see this memory impairment with people that have head injury-induced tinnitus. People have reported impaired working memory and high depression and anxiety score. So if you look at a whole population of people with tinnitus, have many of them come in with depression.
Now, what's sort of interesting about that, there's a part of the brain -- remember when I showed you the first imaging study when I showed you the auditory cortex was activated when people clenched their jaw. And the other part of the brain that I showed you that was activated was the hippocampus.
And so the hippocampus is sort of an interesting structure because it's the part of the brain you use to try to remember where you parked your car in the parking lot when you came in today. So it's important for developing -- having working memory, memory acquisition and retention. And people that have damaged hippocampi basically have impaired working memory.
The other interesting thing about this part of the brain is if you put electrodes in like the ones I just showed you and record from cells in the hippocampus, when these animals walk through the environment, you record from cells that are called place cells. So when an animal walks to a certain location, the cells fire like mad, and they go to another location and they stop firing. So they have these -- a map of space.
The other thing about the hippocampus, it's thought to be involved in emotion and mood. If you basically stress somebody out, you can suppress neurogenesis. I don't know if you know this, but this is a part of the brain, the hippocampus and the subventricular zones, are two parts of the brain where there's new neurons produced during life. Even in humans. And if you're stressed

out, depressed, you suppress neurogenesis. If I give you an antidepressant, basically that will increase neurogenesis.
So these are some studies that were done by some colleagues, Pim van Dijk and Jennifer
Melcher and this guy Langers in the Netherlands. And what they did is they did sort of a network analysis. You can see the cochlear nucleus, inferior colliculus, medial geniculate bodies. These are all part of the auditory pathways. And this is the auditory cortex over here.
And these are different regions of the brain. This is the insula, this is caudate, this is the hippocampus, this is the amygdala. So a couple of these areas might be important over here.
The hippocampus is important for memory. Amygdala is basically thought to play an important role in things like fear.
And when they did this in network analysis, one of the things they found is sound goes up, it actually produced -- once it gets to the medial geniculate, there's strong connection between the medial geniculate body and the hippocampus. And you can see the strength of the correlation -- or activity in these two areas is very, very strong. So it looks like there's strong connections between the auditory system and the hippocampus. You also see connections with the amygdala, which is an emotional area of the brain.
So this is some data collected from my colleague in Germany, in Regensburg, Landgrebe. And what they did is they did what's called a voxel-based morphometry. They looked for changes in hippocampus volume. They get the people in that have tinnitus and they try to compare the volume, the size of the hippocampus in people that have tinnitus and those that don't. And what they did, the whole brain and the only area that showed up as showing having decreased volume was the hippocampus.
So that was a very nice study. And that sort of leads us into this idea that the hippocampus is very important for neurogenesis. There's a stem cell niche in this area in the dentate gyrus. And if you look in a rat, about 9,000 new neurons are born in the rat every day. And by about two months these neurons become electrophysiologically mature. They seem like they integrate themselves into the hippocampal region.
So what we wanted to do is see if we deafened animals and then maybe induced tinnitus what would happen in the hippocampus. So I had a postdoc from Germany that was working with me.
We basically unilaterally exposed some rats, made them deaf in one ear, and you get a lot of destruction of the sensory cells, almost complete wipeout in the one ear.
And then what we did is we measured neurogenesis and cell proliferation. So there's a protein called doublecortin, and these are doublecortin-labeled neurons. Doublecortin is a marker for a neuron that's really a baby neuron. And as they mature this marker goes away.
So if you look in the normal hippocampus, you see a lot of doublecortin-labeled cells. You can see the cell body and the processes. If we blast these animals, ten weeks after we induce this hearing loss, we see a huge suppression in neurogenesis. And this is quantified over here in this bottom graph. These are naive controls, sham controls, and these are noise-exposed animals.
You see a huge reduction. We had hoped to see a correlation between animals that had no tinnitus and animals that had tinnitus. We didn't see much of a difference between the two.
So tinnitus --

>>: [inaudible] make a point that [inaudible] somehow memory function [inaudible].
>> Dr. Richard Salvi: That leads me into my next slide. Before I go to the next slide, I'm going to go back here. We're getting a reduction in newborn neurons. Why are we getting a reduction in newborn neurons. Well, you can use different markers of cell proliferation. There's a marker called Ki67 that labels newborn cells, not neurons. And, again, you see about a 50 percent reduction over here.
So I was set up for the next question, and that is does this lead to memory impairment. And I don't know for sure right now, but these are very preliminary data. So what we did is we took some animals and we ran them on a test called the Barnes maze. And the Barnes maze, you have -- you put this animal in the center of this chamber over here and there's like 18 to 20 holes and there's an escape chamber over here.
So this room is brightly lit. There's a fan going. And rats don't like to be in a bright environment because a predator might sort of seek them out, and they don't like to be in a windy environment.
So what they do is they look around over here and they find a place to escape to. It's a dark chamber that they can hide in. And then what we do is we measure how long it takes to find this.
So the first day when you come to Microsoft you park your car in the lot, right, and you walk out and you say, jeez, where did I park my car. And it takes you a while to find it. But if you park in the same spot every day what happens is you get faster and faster and faster.
So we do the same sort of test over here. We measure the amount of time it takes to find your car or the escape chamber. We measure this in control animals over here. So it takes them about
150 milliseconds on the first day of work. The second day we test them usually about 20-minute intervals. The second time, third time and forth time. You can see the gradual improvement in memory. So it looks like they're learning this memory task.
We have another group of animals that got exposed to exactly the same noise I showed you suppressed neurogenesis. And these guys over here, they're the same -- take the same amount on the first trial because they don't know where the car is, so they should be the same as a controls.
But on trial second, 2, 3, and 4, they're actually much slower. Looks like they're not learning this task.
So what we think is this thing called noise-induced hearing loss in tinnitus turns out I think going to be a very complicated phenomenon. It basically involves a lot of remodeling of the brain. I showed you when you deafened animals how the auditory cortex gets taken over by the somatosensory cortex and other sensory systems.
But there's another part of this I think that was surprising, is not only are these damage to the ear affecting the auditory centers of the brain but it's also affecting so-called nonauditory areas like the hippocampus where you get a big reduction in neurogenesis.
What's interesting about this is if you're going deaf does that mean you're losing some of your memory capabilities. And we don't know the answer to that. But you certainly see a big reduction in neurogenesis. Yes.

>>: Is it that [inaudible] or is it that person gets depressed because they have this injury or loss that they're experiencing and that depression is inhibiting their neurogenesis?
>> Dr. Richard Salvi: We don't know that. These are really like data that were just published earlier this year. But we actually have tests of depression that we can run on the animals where we've actually run some and it looks like there might be a little bit of depression involved.
But one of the ways you can reverse this is to give animals an antidepressant. So if you take a drug like fluoxetine, which is a well-known antidepressant, I don't know what the trade name is, maybe Zoloft is one, lithium chloride is another one, all of those stimulate neurogenesis.
So the question was if you gave these animals fluoxetine or lithium chloride could you stimulate neurogenesis again and could you get rid of some of these memory impairments that go with that. And we actually haven't done the experiments yet.
So usually what happens when I get done with these talks people say yeah, okay, great, interesting story, but what can you do for me right now. And I got a grant a few years ago and people would call me up and said do you have the cure for tinnitus? No. Said can I call you back in six months and let me know or contact me in six months and tell me what you found out.
So there are actually a number of things that you can do that I think are quite effective. So I mentioned a lot of times when you get tinnitus you have a hearing loss. And one of the things that actually works quite well for suppressing tinnitus is a hearing aid. And the reason a hearing aid works, it takes the background noise from the fans, the projectors, and it sort of amplifies them a little bit. And when you get some background noise in the room, that puts activity back into the ear and it actually seems like it tamps down and suppresses the tinnitus.
So if that doesn't work, you can get a sound generator. There's a couple of therapies. There's a company now called Neuromonics. They have commercialized the sound therapies. It's a combination of counseling and sound, pleasant sounds. Before that there was a thing called tinnitus retraining therapy.
So they actually put a sound generator into your ear. They counsel you. And basically the sound is supposed to get you to not focus on your tinnitus, to -- basically you're not supposed to attend to it. So the idea there is it basically tries to retrain the brain.
I think the most provocative piece of evidence, however, that neural activity is critical for keeping tinnitus at bay is work done on cochlear implants. So there's a group in Belgium, Paul
Van de Heyning, and what they did is they got about 20 to 30 people that were completely deaf in one ear. These people had just like intractable tinnitus. They've gone through all the therapies and they just basically can't stand it.
And what they did for these people, they normally would not be candidates for a cochlear implant because in order to get a cochlear implant you have to be deaf in both ears. These people were deaf in just one ear. So they took the deaf ear and they implanted it. And what they found is all of them had a significant reduction in their tinnitus.
So remember what the cochlear implant does. What the cochlear implant does is it -- there are no hair cells so this bypasses it. What you're doing is you're electrically simulating the auditory

nerve. And when you stimulate the auditory nerve you're putting activity back into the brain.
And when you do that the tinnitus goes away.
In fact, if you talk to most cochlear implant users, when they turn their implant off, the tinnitus usually emerges. When they turn the implant on, the tinnitus goes away. So we think it's basically the input to the brain is kind of either whether you put it in by a hearing aid, a sound generator, or cochlear implant. These work for a large proportion of the people. Brian?
>>: So, yeah, I had the question about caffeine. So caffeine has mild antidepressant effects --
>> Dr. Richard Salvi: That's why I drink it every day.
[laughter]
>>: Same here. A glass of wine. Might that be a way of explaining why there were mixed messages with respect to the caffeine [inaudible] that on one hand it might act as a stimulant or enhancer of neurogenesis, on the other hand it might have detrimental effects --
>> Dr. Richard Salvi: It's possible. I don't think there's been really a lot of convincing studies either way for or against using caffeine. I think the best thing what I usually tell people that call me up if they have tinnitus, I said this is really an emerging field. There are really no well-known therapies.
So I think the best thing to do is think of yourself as an experimental subject. If you think that caffeine is doing something to your tinnitus, stop drinking it for a month and reintroduce it. See if it modulates your tinnitus. There are people that have foods that they take that sort of really ramp up their tinnitus. I had a couple people tell me if they take a piece of chocolate, if they do that, their tinnitus goes right through the roof.
Well, if you do that, just don't eat chocolate. And the same thing goes for all these other things.
People tell me if they have a glass of red wine it will make their tinnitus better. Other people say if they have a glass of red wine it will make it worse. So we don't really know all the things that sort of drive the neural circuitry for tinnitus.
One of the big problems with tinnitus right now is it's a phrase, it's a catch-all term. So there are -- just like cancer, there's many different types of cancer. So we don't really have ways of compartmentalizing the different types of tinnitus.
There are people that when you -- if you play -- we have people come into our clinic for evaluation. If you put a really low-level mask or sound in, just put a 30 dB sound in, their tinnitus just goes -- wipes right out. We have other people that come in, we put the masker in, they can still hear their tinnitus, you turn up the masker, the tinnitus just keeps rising up above it.
So they seemed like they're -- they don't respond to the sound generator. And those are the people that probably are going to be the most difficult to treat. They probably fall into the different category.
>>: I think that my other question because you said the example when you implanted cochlear implants on people that oftentimes their symptoms would vanish and maybe essentially they probably aren't providing a very, very clean acoustic signal to the central auditory system and

maybe potentially all they're doing is [inaudible] the noise on the cochlear implant itself is acting as a masker.
>> Dr. Richard Salvi: Yeah. We don't know if it's acting as a mask or just kind of up regulating the activity in the brain.
There are -- it's interesting. We have people -- I had a woman call me up about two weeks ago and she said Dr. Salvi, I really have bad tinnitus. And just by talking to her on the phone I knew that she had a really bad hearing loss. I was yelling on the phone. And she was saying I have a phone at home that has a loudness button on it, and so she had her phone turned up very loud, and I was screaming at her on my phone. And even with those conditions she could barely hear me. She was making out about 50 percent of the conversation.
And when I tried to coax her into getting a hearing aid, she said I don't want to get a hearing aid.
She said when I get a hearing aid I hear all the things like the fan and the refrigerator going on.
So this is a person that needed to get some stimulation into their brain but had been deaf for so long when you put any sound in she didn't like it.
And a lot of the cochlear implant patients, if they've been deaf for a long time, when you first put the cochlear implant in, they don't like it because they start hearing all the sounds in their environment.
I have a friend of mine that just got a hearing aid and one of the things he said, jeez, I can hear all this stuff in the environment I couldn't hear before. So he was walking around in silence most of the time because he had such a big hearing loss.
I think I'll wrap it up over here. I think this is an emerging area. There's some really exciting things going on with the imaging. And the big problem is almost no money has been spent on doing the research. If you think back to the ten -- $1 billion that the VA is paying for health care over here, seems like they ought to try to reduce their costs in some way by trying to figure out effective treatments.
So I'll stop here. These are some of the organizations that supported our research.
[applause]
>> Dr. Richard Salvi: Thank you.