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
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.
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.
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.
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- A team of researchers identified a total of 26 possible adverse reactions to cannabis use.
- Coughing fits, anxiety, and paranoia are among the top three most common adverse reactions to smoking weed.
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The most common adverse effects of pot<p>As it turns out, coughing fits are among the top three most common adverse reactions to cannabis use, along with anxiety and paranoia, according to a new study published in the <em>Journal</em><a href="https://jcannabisresearch.biomedcentral.com/articles/10.1186/s42238-019-0013-x" target="_blank"><em> of Cannabis Research</em></a>. </p><p>Now that weed is legal in the state, a team of researchers at Washington State University sought to document potential negative reactions to cannabis in order to paint a detailed picture of the effects of smoking weed for newbies. The authors surveyed more than 1,500 college students on the specific type and frequency of adverse reactions they had experienced while using pot. Additionally, the students in the study were surveyed about their demographics, personality traits, reasons for using cannabis and their use patterns. </p><p>Despite marijuana's <a href="https://bigthink.com/sex-relationships/marijuana-sex" target="_self">numerous benefits</a>, the team identified a total of <a href="https://jcannabisresearch.biomedcentral.com/articles/10.1186/s42238-019-0013-x/tables/2" target="_blank">26 possible adverse reactions to</a> the drug. More than half of the study participants reported having coughing fits along with anxiety and/or paranoia while using cannabis. The most frequently occuring of these were the coughing fits, along with chest/lung discomfort and body humming. A subset of the study group reported these reactions occurring around 30–40% of the time they were using pot. On the flip side, the three <em>least</em>-commonly reported reactions to cannabis use were fainting, visual hallucinations and cold sweats. </p><p>"There's been surprisingly little research on the prevalence or frequency of various adverse reactions to cannabis and almost no research trying to predict who is more likely to experience these types of adverse reactions," <a href="https://news.wsu.edu/2020/03/30/new-research-sheds-light-potentially-negative-effects-cannabis/" target="_blank">said Carrie Cuttler</a>, assistant professor of psychology and an author on the paper, according to WSU News. "With the legalization of cannabis in Washington and 10 other states, we thought it would be important to document some of this information so that more novice users would have a better sense of what types of adverse reactions they may experience if they use cannabis."</p><p>The most distressing of the 26 negative reactions were panic attacks, fainting, and vomiting. Yet, the survey data suggested that cannabis users generally do not find even acute adverse reactions to cannabis to be severely distressing.</p>
What causes a bad reaction?<img type="lazy-image" data-runner-src="https://assets.rebelmouse.io/eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJpbWFnZSI6Imh0dHBzOi8vYXNzZXRzLnJibC5tcy8yMjkwOTEwOC9vcmlnaW4uanBnIiwiZXhwaXJlc19hdCI6MTYyNTQ5MDQ2Mn0.S2Pkbh3VAgB4Gk5tkavamMv0_4t76dg65yGWpCHG17U/img.jpg?width=1245&coordinates=0%2C1872%2C0%2C1252&height=700" id="dee45" class="rm-shortcode" data-rm-shortcode-id="df6e30ecae156ba0012f4773a374800c" data-rm-shortcode-name="rebelmouse-image" />
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