Treatable brain inflammation may be behind tinnitus

Scientists may have seen a way to cure a maddening symptom of hearing loss.

  • A treatment for tinnitus – a constant ringing in the ears – has been frustratingly elusive.
  • Out-of-control inflammation, the brain's response to damage, may be the cause of long-term ringing in the ears.
  • A study that examined mice with noise-induced hearing loss seems to have found the neural trigger for tinnitus.

Common, or subjective, tinnitus is no fun. If you have it, you know what we mean. And a lot of people do — some 500 million worldwide. It's a byproduct of hearing loss that produces a constant veil of high-frequency pitches that never abates. For sufferers, there is no silence, ever. Unfortunately, identifying its cause, much less a treatment, has proven elusive. Now, however, a new study published in PLOS Biology may have uncovered the physiological mechanism behind it: neuroinflammation in the auditory cortex. And it could be treatable.

Note the "may" in the paragraph above. It's there because this study draws its conclusions based on the physiology of rodent test subjects, not humans, and things don't always translate between species. Hence, its claims deserve a grain or two of salt. Ethics issues aside, this is often the case with exciting-sounding medical-breakthrough news. It's so common, in fact, that there's a Twitter hashtag for it: @justsaysinmice.

How to acquire tinnitus

Image source: Vagengeim/Yes - Royalty Free/Shutterstock/Big Think

Not that you'd want to. However, the recipe is simple: Expose your ears to overloud noise. Tinnitus is actually not an underlying condition — it's a symptom of hearing loss. Noise-induced hearing loss (NIHL) can result from, for example, working in a loud environment without protecting your ears, or attending too many loud concerts, standing too close to speakers at a show, or from listening to loud music on headphones.

The way that we hear sound is not as direct as many think. Sound is really a matter of compression waves generated by a source that compresses and releases air on its way to your ears. Tiny hairs, the stereocilia, in your ears receive these air-pressure changes and fire off signals to your brain that we interpret as sound. Each hair has the job of producing a certain range of audio frequencies, and with tinnitus, some of these hairs get stuck in what amounts to their "on" position, continually firing off these signals to your brain even without the presence of an actual external sound source. Exactly what triggers this misbehavior is what the new study attempts to explain.

Inflammation

Image source: Alila Medical Media/Shutterstock

The study states, "Neuroinflammation is the central nervous system's response to external and internal insults, such as infection, injury, diseases, and abnormal neural activity," and so its authors looked at mice with NIHL to assess its possible role in tinnitus. They conclude "Our results indicate that neuroinflammation plays an essential role in a noise-induced excitatory-to-inhibitory synaptic imbalance and tinnitus in a rodent model."

To protect the brain, an inflammatory response typically involves the activation of microglia, the central nervous system's primary immune cells. When they remain active in response to chronic damage — as with hearing damage — though, they tend to release proinflammatory cytokines, which can make the problem worse. In the mice studies, the authors found one such proinflammatory cytokine, TNF-α. ("TNF" stands for "tumor necrosis factor.") It seems to be the neural trigger for tinnitus.

When the researchers shut off the gene that results in the production of TNF-α in one set of mice, and likewise when they repressed it with medication in another, tinnitus disappeared. Testing the connection from the other direction, they also found that when they introduced TNF-α into the auditory cortex of normal mice and also mice who had no natural TNF-α, tinnitus appeared.

How do we know if a mouse has tinnitus?

Image source: photolinc/Shutterstock

This question, which may have occurred to you to wonder, highlights a potential problem with this study. Since tinnitus is an ever-present phenomenon, some in the research community — including the authors of this study — have embraced "gap detection" as a means of testing for the presence of the condition in animals. The idea of gap testing is that, since tinnitus is constant, an animal wouldn't be able to hear gaps between a series of audio tones being played. Gap detection is tested by monitoring an animal's acoustic startle reflex to each new tone as it sounds — in theory, an animal with tinnitus won't notice or react to each new tone. However, it's worth noting that the value of gap detection testing for tinnitus is controversial.

And so...

All that having been said, there are a number of anti-inflammatory medications, and as used in the research, genetic means of controlling the presence of TNF-α. If the authors' findings are eventually confirmed to be valid in human subjects, there may be hope for tinnitus sufferers at last.

Befriend your ideological opposite. It’s fun.

Step inside the unlikely friendship of a former ACLU president and an ultra-conservative Supreme Court Justice.

Sponsored by Charles Koch Foundation
  • Former president of the ACLU Nadine Strossen and Supreme Court Justice Antonin Scalia were unlikely friends. They debated each other at events all over the world, and because of that developed a deep and rewarding friendship – despite their immense differences.
  • Scalia, a famous conservative, was invited to circles that were not his "home territory", such as the ACLU, to debate his views. Here, Strossen expresses her gratitude and respect for his commitment to the exchange of ideas.
  • "It's really sad that people seem to think that if you disagree with somebody on some issues you can't be mutually respectful, you can't enjoy each other's company, you can't learn from each other and grow in yourself," says Strossen.
  • The opinions expressed in this video do not necessarily reflect the views of the Charles Koch Foundation, which encourages the expression of diverse viewpoints within a culture of civil discourse and mutual respect.
Keep reading Show less

3 ways to find a meaningful job, or find purpose in the job you already have

Learn how to redesign your job for maximum reward.

Videos
  • Broaching the question "What is my purpose?" is daunting – it's a grandiose idea, but research can make it a little more approachable if work is where you find your meaning. It turns out you can redesign your job to have maximum purpose.
  • There are 3 ways people find meaning at work, what Aaron Hurst calls the three elevations of impact. About a third of the population finds meaning at an individual level, from seeing the direct impact of their work on other people. Another third of people find their purpose at an organizational level. And the last third of people find meaning at a social level.
  • "What's interesting about these three elevations of impact is they enable us to find meaning in any job if we approach it the right way. And it shows how accessible purpose can be when we take responsibility for it in our work," says Hurst.
Keep reading Show less

Physicist advances a radical theory of gravity

Erik Verlinde has been compared to Einstein for completely rethinking the nature of gravity.

Photo by Willeke Duijvekam
Surprising Science
  • The Dutch physicist Erik Verlinde's hypothesis describes gravity as an "emergent" force not fundamental.
  • The scientist thinks his ideas describe the universe better than existing models, without resorting to "dark matter".
  • While some question his previous papers, Verlinde is reworking his ideas as a full-fledged theory.
Keep reading Show less

UPS has been discreetly using self-driving trucks to deliver cargo

TuSimple, an autonomous trucking company, has also engaged in test programs with the United States Postal Service and Amazon.


PAUL RATJE / Contributor
Technology & Innovation
  • This week, UPS announced that it's working with autonomous trucking startup TuSimple on a pilot project to deliver cargo in Arizona using self-driving trucks.
  • UPS has also acquired a minority stake in TuSimple.
  • TuSimple hopes its trucks will be fully autonomous — without a human driver — by late 2020, though regulatory questions remain.
Keep reading Show less