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Treatable brain inflammation may be behind tinnitus

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

Image source: Alex Iby/Unsplash/Big Think
  • 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.

Hulu's original movie "Palm Springs" is the comedy we needed this summer

Andy Samberg and Cristin Milioti get stuck in an infinite wedding time loop.

Gear
  • Two wedding guests discover they're trapped in an infinite time loop, waking up in Palm Springs over and over and over.
  • As the reality of their situation sets in, Nyles and Sarah decide to enjoy the repetitive awakenings.
  • The film is perfectly timed for a world sheltering at home during a pandemic.
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Two MIT students just solved Richard Feynman’s famed physics puzzle

Richard Feynman once asked a silly question. Two MIT students just answered it.

Surprising Science

Here's a fun experiment to try. Go to your pantry and see if you have a box of spaghetti. If you do, take out a noodle. Grab both ends of it and bend it until it breaks in half. How many pieces did it break into? If you got two large pieces and at least one small piece you're not alone.

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Our ‘little brain’ turns out to be pretty big

The multifaceted cerebellum is large — it's just tightly folded.

Image source: Sereno, et al
Mind & Brain
  • A powerful MRI combined with modeling software results in a totally new view of the human cerebellum.
  • The so-called 'little brain' is nearly 80% the size of the cerebral cortex when it's unfolded.
  • This part of the brain is associated with a lot of things, and a new virtual map is suitably chaotic and complex.

Just under our brain's cortex and close to our brain stem sits the cerebellum, also known as the "little brain." It's an organ many animals have, and we're still learning what it does in humans. It's long been thought to be involved in sensory input and motor control, but recent studies suggests it also plays a role in a lot of other things, including emotion, thought, and pain. After all, about half of the brain's neurons reside there. But it's so small. Except it's not, according to a new study from San Diego State University (SDSU) published in PNAS (Proceedings of the National Academy of Sciences).

A neural crêpe

A new imaging study led by psychology professor and cognitive neuroscientist Martin Sereno of the SDSU MRI Imaging Center reveals that the cerebellum is actually an intricately folded organ that has a surface area equal in size to 78 percent of the cerebral cortex. Sereno, a pioneer in MRI brain imaging, collaborated with other experts from the U.K., Canada, and the Netherlands.

So what does it look like? Unfolded, the cerebellum is reminiscent of a crêpe, according to Sereno, about four inches wide and three feet long.

The team didn't physically unfold a cerebellum in their research. Instead, they worked with brain scans from a 9.4 Tesla MRI machine, and virtually unfolded and mapped the organ. Custom software was developed for the project, based on the open-source FreeSurfer app developed by Sereno and others. Their model allowed the scientists to unpack the virtual cerebellum down to each individual fold, or "folia."

Study's cross-sections of a folded cerebellum

Image source: Sereno, et al.

A complicated map

Sereno tells SDSU NewsCenter that "Until now we only had crude models of what it looked like. We now have a complete map or surface representation of the cerebellum, much like cities, counties, and states."

That map is a bit surprising, too, in that regions associated with different functions are scattered across the organ in peculiar ways, unlike the cortex where it's all pretty orderly. "You get a little chunk of the lip, next to a chunk of the shoulder or face, like jumbled puzzle pieces," says Sereno. This may have to do with the fact that when the cerebellum is folded, its elements line up differently than they do when the organ is unfolded.

It seems the folded structure of the cerebellum is a configuration that facilitates access to information coming from places all over the body. Sereno says, "Now that we have the first high resolution base map of the human cerebellum, there are many possibilities for researchers to start filling in what is certain to be a complex quilt of inputs, from many different parts of the cerebral cortex in more detail than ever before."

This makes sense if the cerebellum is involved in highly complex, advanced cognitive functions, such as handling language or performing abstract reasoning as scientists suspect. "When you think of the cognition required to write a scientific paper or explain a concept," says Sereno, "you have to pull in information from many different sources. And that's just how the cerebellum is set up."

Bigger and bigger

The study also suggests that the large size of their virtual human cerebellum is likely to be related to the sheer number of tasks with which the organ is involved in the complex human brain. The macaque cerebellum that the team analyzed, for example, amounts to just 30 percent the size of the animal's cortex.

"The fact that [the cerebellum] has such a large surface area speaks to the evolution of distinctively human behaviors and cognition," says Sereno. "It has expanded so much that the folding patterns are very complex."

As the study says, "Rather than coordinating sensory signals to execute expert physical movements, parts of the cerebellum may have been extended in humans to help coordinate fictive 'conceptual movements,' such as rapidly mentally rearranging a movement plan — or, in the fullness of time, perhaps even a mathematical equation."

Sereno concludes, "The 'little brain' is quite the jack of all trades. Mapping the cerebellum will be an interesting new frontier for the next decade."

Economists show how welfare programs can turn a "profit"

What happens if we consider welfare programs as investments?

A homeless man faces Wall Street

Spencer Platt/Getty Images
Politics & Current Affairs
  • A recently published study suggests that some welfare programs more than pay for themselves.
  • It is one of the first major reviews of welfare programs to measure so many by a single metric.
  • The findings will likely inform future welfare reform and encourage debate on how to grade success.
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