The Ring to Rule Them All – Tinnitus

Posted by dknowland on August 3, 2017 in Neurological Disorders, Neuroscience, Neuroscience in pop culture | Leave a comment

Baby Driver, the most recent theatrical offering from director Edgar Wright (Hot Fuzz, Scott Pilgrim vs. The World), not only makes the first generation iPod (which now passes as a body double for a paperweight) look cool again, but also brings to light an interesting auditory condition that affects nearly 10% of the population – tinnitus.

The first generation iPod: once a state-of-the-art mp3 player, now a benchmark of which century you were born in.

The premise of the movie centers on Baby, a young twenty-something getaway driver seemingly transplanted from the Fast and the Furious universe, who listens to music in order to drown out the constant ringing in his ears. Music is essential for his ability to focus, pay attention, and execute sprawling drifts across the city.

Tinnitus (ti-NIGHT-us or TINN-a-tus, both are accepted), a condition that manifests as the constant perception of phantom noises, is most commonly experienced as a buzzing, ringing, or whirring sensation in the absence of any actual noise. Tinnitus is derived from the latin word meaning “to ring” or “tinkle”, which may sound borderline pleasant, however, those afflicted with it report it to be anything but.

You might have personally experienced something similar that offers a kind of parallel to what tinnitus sufferers hear. If you’ve ever attended a concert and afterwards experienced a persistent ringing sensation in your ears after you’ve gone home, this provides a good idea of what tinnitus is like.

Tinnitus is not actually a standalone condition, but rather a symptom of many other disorders. Tinnitus can be observed in patients with major depressive disorder, traumatic brain injury, and damage from ototoxic (the fancy medical term for damage to the ear) drugs. Most commonly, however, tinnitus results from either age-related or noise-induced hearing loss. While roughly 10% of the population suffers from tinnitus–a number that increases in people 70 years or older-–the extent to which it affects the daily lives of individuals varies considerably. In a survey of over 1,000 tinnitus sufferers, nearly 40% report it having little to no impact on their lives. Nevertheless, over 50% of individuals report a significant impact to some degree in their lives ranging from trouble concentrating to even the extremes of being unable to work [1].

Although there is a relatively high prevalence of tinnitus, 34% of sufferers report it to be “annoying, but does not significantly impact life.” Also known as the losing a sock every time you do laundry effect.

So, what causes tinnitus and what does it have to do with the brain? Valid questions. To answer them, we need to take a quick sidebar and review on how we hear.

A quick sidebar and review on how we hear

Sounds in the environment, such as from an annoying co-worker that won’t stop playing with a fidget spinner, initiate as sound waves and enter our ear canal-–the part of our ear that was a victim of “wet willys” as a child. These sound waves propagate through the canal until they vibrate the tympanic membrane, or eardrum. The eardrum is connected to a series of three bones called the malleus, incus, and stapes, which incidentally sounds like a great name for a Crosby, Stills, and Nash influenced indie folk band. When the eardrum vibrates in response to your coworker’s fidget spinner, it sets into motion these three bones that results in the stapes vibrating against a structure in your inner ear called the cochlea. The cochlea is a fluid-filled snail-shaped structure (aptly named, cochlea is latin for “snail”) that contains many “hair cells” along its inside (they’re called hair cells but actually have little in common with what’s on your head). This is where the magic happens. To discriminate different frequencies of sounds, the vibration initiated by the stapes produces ripples in the fluid surrounding the cochlea. Depending on the pitch of the sound, the frequency of these ripples will change and subsequently activate a specific set of hair cells along the length of the cochlea. In essence, we’ve taken sound waves, translated them into liquid motion, and produced electrical signals.

As a metaphor, imagine you unravel the cochlea from a spiral to an elongated plank. Along this plank are a bunch of hair cells that respond to different frequencies. Think of it like a xylophone. Depending on which part along the length of the xylophone you hit, you produce a different sound. Once the hair cells are activated they send signals to the brain (I told you we’d get to the brain) where further fine processing in the auditory thalamus and auditory cortex occurs that results in the sensation of hearing. N.B. For a great visual review on how we hear check this video out.

Cartoon of the structures in your ear responsible for transforming sound waves into what we perceive as actual sounds. The cochlea is the structure on the right side that looks like a finger making a creepy “come hither” motion. 

Brain vs. the ear, what causes tinnitus?

Scientists are still unsure of what causes tinnitus; but they have some ideas. Since the most common health condition associated with tinnitus is hearing loss (some researchers even believe that hearing loss is a prerequisite for tinnitus), scientists believe that damage to the inner ear must be the culprit. The prevailing theory is that prolonged exposure to loud noises or even a particularly intense acute event permanently damages the hair cells – the ones in the cochlea that transduce sound waves into electrical signals. Depending on which hair cells are damaged, the ability to hear a certain frequency will be lost. However, the brain being an organ of immense adaptability and overachievement, adapts to the fact that it no longer receives signals from these damaged hair cells by filling in the blanks, even in the absence of any actual sound. The cruel irony is that what you’ve lost in hearing, you gain in a perpetual tone in the particular frequency that was damaged in the first place [2].

This paradoxical situation is why scientists believe that the brain may be the key in treating tinnitus. The distinction of where tinnitus is maintained is critical-–it informs where interventions and treatment should be directed. If the problem was simply ear-centric, then the death of hair cells would simply result in loss of hearing. Thus, while tinnitus may be initiated in the ear, the prolonged maintenance likely resides in the brain.

Some of the most convincing evidence for tinnitus representing a brain-related issue comes from studies which sever the auditory nerve. Essentially, all input from the ear to the brain has been cut off. If tinnitus originates in the ear, then eliminating communication to the brain should abolish tinnitus. However, the phantom ringing percept persisted in tinnitus patients even after the ear-to-brain connection was severed, suggesting that some process in the brain was responsible for the maintenance of tinnitus [3].

More recent studies lend support to this hypothesis. Researchers reported increases in neural activity in the primary auditory cortex (the part of the brain that processes auditory information after it has left the ear) after inducing noise-induced hearing loss which persisted after the initial trauma [4]. If these findings are true, then reducing hyperactivity in the auditory cortex might represent an attractive target for therapeutic intervention.

Other studies have shown changes in default mode network (DMN) activity in patients with tinnitus. The DMN is a series of highly connected cortical structures that are activated at wakeful rest. In slightly less scientific terms, it is a group of brain areas that are activated when you are spacing out or daydreaming. Using brain imaging techniques, researchers showed that DMN activity was reduced in patients experiencing tinnitus-related distress [5]. 

Default mode network (DMN), personified.

This then might suggest that one of the most salient features of tinnitus-related distress is simply patients focusing on the ringing. Suggesting that your own attention to your condition might be an underlying cause is almost like when you had that annoying sibling who would air punch you inches from your face and tell you to ignore it because they’re not actually hitting you. Which brings us to the treatments currently available for tinnitus sufferers.

Treatments and beyond

To date, there is no cure for tinnitus. Some groups have attempted to leverage our limited knowledge we have about the neural underpinnings of tinnitus to target the brain as treatment. Most commonly, researchers have used transcranial magnetic stimulation, a non-invasive method to introduce electrical current into areas of the brain, in order to reduce the loudness and frequency of tinnitus. These studies have been met with mixed results ranging from slight improvement to no change [6, 7].

The most effective treatments to date have been a combination of cognitive behavioral therapy (CBT) or mindfulness training with sound therapy. Cognitive behavioral therapy and mindfulness often focus on the patient’s ability to accept tinnitus as part of their life and to either coexist or ignore it. One study has even shown that behavioral therapy increases DMN activity (i.e. improved zoning out) which correlated with the improvement in tinnitus severity patients experienced [8]. Sound therapy, on the other hand, involves masking tinnitus by playing other tones or soothing sounds over it.

Unfortunately, simply learning to ignore it is currently the most effective treatment for tinnitus.

While these seem like imperfect treatments, the idea of training patients to ignore their tinnitus is not trivial. It was previously mentioned that conditions associated with tinnitus include difficulty sleeping and depression/anxiety. It is fair to wonder which condition begets which. Although tinnitus is classified as a symptom of depression and sleep problems, it is reasonable to think that if the constant ringing is loud and persistent enough, then it could severely interfere with one’s ability to fall asleep. If it becomes pervasive to the extent of affecting all aspects of daily life, then you can imagine the effect the condition would have on overall well-being. Hair cells in the ear actually connect with parts of the limbic system, the brain system typically involved in emotion, so it follows that tinnitus may have a significant emotional impact on the afflicted.

An old thought experiment goes, “If a tree falls in a forest and no one is around to hear it, does it make a sound?” Considering the direction of current tinnitus treatment, we might amend this to, “If a person successfully ignores his or her tinnitus, does it exist?” Towards this goal, much effort has focused on CBT and mindfulness training. While more effective technologies focusing on ear aids or sound therapies that address the underlying cause remain to be developed, for now it appears that ignoring the falling tree may be our best recourse.

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The author is a 4th year graduate student who has been living with noise-induced hearing loss tinnitus for the last 6 years. He recommends wearing earplugs at concerts, and sleeps with a fan constantly buzzing.

References

1. https://www.ata.org/understanding-facts
2. Henry, James A., Kyle C. Dennis, and Martin A. Schechter. “General review of tinnitus: prevalence, mechanisms, effects, and management.” Journal of speech, language, and hearing research 48.5 (2005): 1204-1235.
3. House, John W., and D. E. Brackman. “Tinnitus: surgical treatment.” Ciba foundation symposium. Vol. 85. 1981.
4. Norena, A. J., and J. J. Eggermont. “Changes in spontaneous neural activity immediately after an acoustic trauma: implications for neural correlates of tinnitus.” Hearing research 183.1 (2003): 137-153.
5. Lanting, Cris, et al. “Tinnitus-and task-related differences in resting-state networks.” Physiology, Psychoacoustics and Cognition in Normal and Impaired Hearing. Springer, Cham, 2016. 175-187.
6. Yilmaz, Mehmet, et al. “Effectiveness of transcranial magnetic stimulation application in treatment of tinnitus.” Journal of Craniofacial Surgery 25.4 (2014): 1315-1318.
7. Baguley, David, Don McFerran, and Deborah Hall. “Tinnitus.” The Lancet382.9904 (2013): 1600-1607.
8. Krick, Christoph M., et al. “Cortical reorganization in recent-onset tinnitus patients by the Heidelberg Model of Music Therapy.” Frontiers in neuroscience 9 (2015).