And here is Laurien back again with a crash intro on what is happening in our brain when we hear something! Did you hear that? 😉
A ringing in your ear?
The first post in this BRAIN research series was about language. Next to spoken words, there are plenty of other sounds in our daily life. They are the source of joy and comfort but what if a certain sound drives you mad? Tinnitus is the fancy term for ‘having a ringing in your ear’. It is in fact the perception of sound in absence of any actual sound.
Now, before I go on, I have to emphasize that I am no expert in this field. My PhD is focused on muscle-independent communication for locked-in patients. These are patients who lost most motor capacities and are in essence ‘locked-in’ their own bodies, yet let me tell you more about this another time 😉 . I am writing about tinnitus now because it is a scientific side project of mine and I will collaborate in a clinical investigation soon on it. As a clinician, I have always found it fascinating how such a seemingly insignificant disorder can drive one mad, but try to listen to a few of these 11 tinnitus sounds by the British tinnitus association. Personally, I can imagine going mad when being forced to listen to sound 8 or 11 for even a day.
In April I went to a studium generale lecture here in Maastricht by Prof. dr. Robert Stokroos and Dr. Iris Nowak-Maes. Perhaps some of you were there as well? I remember that extra chairs were brought in to accommodate the immense turn-up that evening. Prof. dr. Stokroos confirmed the immense proportion of this seemingly insignificant disorder:
“About a million people in the Netherlands have to deal with tinnitus, about 60.000 of those are seriously hindered in their daily lives. Tinnitus costs around 2.3 percent of the yearly care budget.”
Ok, so now that we know what tinnitus is. We also know how severe its consequences are in our society. So let’s cut to the chase.
What causes tinnitus? The most common cause is exposure to noise, such as a noisy work environment. People that have been in warfare for example often develop tinnitus. What happens is that the cochlea, the ‘snail house’, of the ear gets damaged.
Specifically, there are tiny hair cells in this snail house that get damaged. But where does neuroscience come in? Well in most cases, damage to these little hair cells causes hearing loss in a specific frequency range. This is because the hair cells are grouped per frequency. What is interesting now is that often the tinnitus frequency is exactly in this frequency range! So what might be happening? Animal models suggest that when the hair cells are damaged, there is differentiation of nerves going from the cochlea to the brain. Our auditory part of the brain starts to have increased spontaneous activity. So what is a disease of the ear, soon becomes a disease of the brain.
Image adopted from Adjamian, P., Sereda, M., & Hall, D. A. (2009). The mechanisms of tinnitus: perspectives from human functional neuroimaging. Hearing research, 253(1), 15-31.
What is often seen in animal models is that there is some reorganization of the auditory cortex (part C of the above figure). You can see that the top red regions stop responding to high frequencies but start reacting on lower frequencies that were close to them. You can see how damage to a specific part of the ear, can change the workings of the brain.
The above is just a common way of thinking about tinnitus. However, be careful dear readers, little is still known about this fascinating topic. One in four tinnitus patients do not have hearing loss namely and reorganization of the auditory cortex has not been confirmed as a cause of tinnitus in humans. However, motivated neuroscientists keep learning and understanding this disease better and better. Once the mechanisms are unraveled, the way is open to treatment and interventions. However, my take home message to those readers that haven’t developed tinnitus yet is: Protect your ears J As always, prevention is better than treatment!
Tinnitus remains a hot topic in the field of neuroscience, we don’t understand it fully yet. There is still a lot more to discover about auditory perception. For example, another strange disorder that involves the hatred of certain specific sounds… but our next guest will unravel the neural correlates of this phenomenon in next week’s post.
by Laurien Nagels-Coune, PhD student in Cognitive Neuroscience at FPN, Maastricht University
With love for Researchers,