- Published on Wednesday, 09 August 2017 14:21
Principal investigator at the Auditory Cognitive Neuroscience Lab (Department of Speech and Hearing Science at the university of Illinois Urbana-Champaign, US), Dr. Fatima T. Husain has been conducting studies on hearing disorders like tinnitus , using computational modeling and brain imaging. She has conceded an interview to Audiology Worldnews in which she exposed how brain imaging is helping to better understand tinnitus and what are the main obstacles for neuroimaging studies in tinnitus patients, like the placebo effect.
From the researcher point of view, what are the specificities of the field of tinnitus?Tinnitus is confusing for everybody. It’s confusing for the patients, for the clinicians and for the researchers. Because you have something that only you and nobody else can hear. And as an observer, I have to believe you. So, how do we know when someone has tinnitus? If you have blood pressure, I can measure it, if you have diabetes, I can also measure it. And there are objective ways to do that. And this is the root of confusion when it comes to tinnitus: the lack of method to measure it objectively. So, we, the researchers, have to be very careful about the way we study tinnitus in order to not add to the confusion!
Brain imaging is the only non-invasive way to objectively assess tinnitus because we have no other test we can run in the clinics or labs. Psychoacoustics measures, that is playing sounds aimed at the characterization of loudness and pitch by the patient, are mostly subjective methods, providing variable results, and I may need to test you many times to get reliable results.
What is the big picture of tinnitus patients and brain imaging?What we’re beginning to see is that different regions of the brain activate differently when we have tinnitus. We can see that when patients are doing a task. Those who don’t have tinnitus can react to a sound, but if you have tinnitus, you react differently. In that sense your reactions can also be shown in brain imaging. The second thing we’re looking at is functional connectivity, especially during the resting state. That means looking at connections between brain regions, if they are “talking” to each other, and how they are talking to each other. With tinnitus, normal connections may have changed.
Does brain imaging help in assessing tinnitus variability?
Measuring variability in tinnitus severity is important, because some people are steady, while others are naturally variable. Depending on when you test them you can have a lot of changes without any intervention. In the future, we should have a better handle on this variability, and actually brain imaging will be helpful. Presently, we are trying to scan the same person twice, one week apart, and we measure their tinnitus reaction. Such resting state studies have been found to be reliable in the healthy population and we want to know if we can find replicable data in tinnitus population too. If we find that certain tinnitus patients are more reliable than others. Is it due to some change in their psychological reaction? Maybe within the week, you add news from your boss. That can happen, maybe the night before you couldn’t sleep well. Anything can change your tinnitus and we’re trying to understand that better. This is a complex topic, and because it is complex, we owe to the field and the patients to be as careful as possible.
Can neuroimaging provide us with objective information, like pitch or loudness, or is it only about psychological characteristics?
Currently, I don’t think you can see much about pitch or loudness. Even though some studies are showing that a little bit, it is not conclusive. I don’t believe our imaging can show the difference between having a tinnitus pitch of 6 kHz or having a pitch of 7 kHz. What is more prominent, or easiest to see, is whether I am bothered or not by it. So, in my opinion, the small differences between the characteristics of sound are not easily imaged. When we’re looking at the brain, we’re looking at volumes of 3 mm3. That’s a lot of tissue, with hundreds of thousands of neurons, and because they are all responding to similar sounds, it is difficult to tell differences to slightly different tones. When you consider psychological reactions, instigated by some tasks, these are easier to image with our tools. There may be a difference for the pitch but our tools are not sufficiently sensitive yet to see it.
What about the interaction of hearing loss in tinnitus?
It is another problem when we’re talking about measuring tinnitus physical characteristics. Patients with hearing loss may have difficulty matching the external sound with their internal one because they cannot hear the external sound very well. Also, in terms of brain imaging what happens when you have hearing loss and tinnitus is that there changes to the connections of the networks that may be due to hearing loss, and not to tinnitus. So we have to be very careful to attribute these changes correctly. In terms of pitch, it depends on topographic organization of responses to tones, and this organization is compromised when you have hearing loss, regardless of tinnitus. In my opinion, earlier studies that looked at tonotopic reorganization and concluded it was a causative factor of tinnitus, whereas it may be a consequence of hearing loss. It maybe a factor for developping tinnitus but I don’t think it is a factor for tinnitus to become chronic or persistent. Pitch and loudness perception may be happening in the brainstem, or in some subcortical regions, and we’re not so good at imaging these regions. We probably need better tools to look at the small structures in the brainstem.
Why resting state functional connectivity is useful for studying tinnitus?
People with constant tinnitus listen to the sound all the time and therefore are in a different state than people without tinnitus. And this can be exploited with resting state studies. We’re not having them doing anything, they are just lying there in the scanner and letting their mind wander... People with tinnitus have an extra sound and they may be attending to the tinnitus which put them in a different state that somebody who does not have tinnitus. This is a pure experiment in that sense and allows us to understand many networks in the brain, those associated with hearing, attention, etc.
Your works also focus on the model of severity and habituation...
When a person starts having tinnitus, after a few months, she/he may wonder if he has a tumor and go to a doctor. When the doctor rules out all other issues, some patients accept it, and others don’t, and keep looking for a solution.
Tinnitus patients may be keeping going to the audiologist, getting fitted with hearing aids, following therapies, maybe undergoing surgeries, and continue to be bothered by tinnitus. So this is what I want to understand. If you look at the loudness of the tinnitus, it may be the same than in other people, but the question is: what makes someone accept it, and others not? Actually, 80% habituate to the sound, whereas 20% may not habituate. They report being anxious, depressed etc. We want to understand how people cope and habituate to tinnitus. We’re doing brain imaging, so we can now scan the individuals in different parts of the continuum of severity and understand it better.
So brain imaging allows to distinguish between people who manage to cope and those who don’t?
Exactly. We are definitely finding differences. The results in our lab appear to be reliable if you account for severity or how bothered people are by their tinnitus and its duration. One of the reasons why the research results may be confusing across different labs is about the duration of tinnitus (how many years and months after its onset), and how have the patient reacted to it.
There are also lots of networks in the brain. The attention and emotional networks are compromised, because you’re attending to tinnitus too much, so you’re exhausted, which leads to fatigue and concentration difficulties, and maybe depression signals. And it’s about feedback loops: I’m stressed, so my tinnitus is louder, and I get more stressed because it is louder. So that’s refl ected in brain imaging patterns in the networks, and the connections and their activity. Both are changed.
In our studies we are finding changes in the default mode network. This network is more active at rest and it is good if it is more active. But we find that it is less active in those with tinnitus and even less active if you have had tinnitus for a long time and if you have severe tinnitus. One key player of the default mode network is the precuneus and its connections are compromised in tinnitus.
What is the future of brain imaging studies in tinnitus patients and possible therapies?
I think in the future we will use brain imaging to identify different subgroups in the larger, heterogeneous tinnitus population. We can use brain imaging to test therapies carefully to see which therapy works with which subgroup. In the past different therapies have been tried with limited success. But now, we can actually see what is changing in the brain, it is a very powerful tool for us, researchers and clinicians to develop new therapies. With respect to therapies, two things to keep in mind are the placebo effect and how important counseling is for effective management of tinnitus severity. Placebo effect is strong. If I want to please my audiologist, or my psychologist, I say that it’s all right even if it isn’t. Sometimes patients can be very isolated, nobody believes he has tinnitus and how much trouble it causes to their daily life. Sometimes, because tinnitus is invisible, there is less sympathy within the family and from the colleagues about the difficulties and the challenges, so when they go to a doctor, or an audiologist, they feel good, and they automatically reduce the annoyance, it doesn’t have to do with the therapy or with the drugs. So counseling is very important and people just feel well when somebody listen to their problems.
Is placebo effect likely to interact in studies?
Yes, if we are not careful in having randomized controlled trials. It is not always simple to create control conditions. It is easy to do with drugs, but not, for instance, with some other therapies. As researchers are becoming more aware about how counseling is important and should be considered within the studies. So, in the case of hearing aids, to control the situation (within-subject), you would provide counseling for six months without fitting them with hearing aids, but you cannot deny someone treatment, which is unethical. Then you can have other control group who doesn’t have tinnitus but is identical in terms of hearing loss. It takes preparation, hard work and lot of money to run good clinical trials.
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Source: Audiology Infos Brazil