Posts Tagged ‘hearing’

It’s well known that exposure to extremely loud noises — whether it’s an explosion, a firecracker or even a concert — can lead to permanent hearing loss.
But knowing how to treat noise-induced hearing loss, which affects about 15 percent of Americans, has largely remained a mystery. That may eventually change, thanks to new research from the Keck School of Medicine of USC, which sheds light on how noise-induced hearing loss happens and shows how a simple injection of a salt- or sugar-based solution into the middle ear may preserve hearing. The results of the study were published today in PNAS.

Deafening sound
To develop a treatment for noise-induced hearing loss, the researchers first had to understand its mechanisms. They built a tool using novel miniature optics to image inside the cochlea, the hearing portion of the inner ear, and exposed mice to a loud noise similar to that of a roadside bomb.

They discovered that two things happen after exposure to a loud noise: sensory hair cells, which are the cells that detect sound and convert it to neural signals, die, and the inner ear fills with excess fluid, leading to the death of neurons.

“That buildup of fluid pressure in the inner ear is something you might notice if you go to a loud concert,” says the study’s corresponding author John Oghalai, MD, chair and professor of the USC Tina and Rick Caruso Department of Otolaryngology – Head and Neck Surgery and holder of the Leon J. Tiber and David S. Alpert Chair in Medicine. “When you leave the concert, your ears might feel full and you might have ringing in your ears. We were able to see that this buildup of fluid correlates with neuron loss.”

Both neurons and sensory hair cells play critical roles in hearing.

“The death of sensory hair cells leads to hearing loss. But even if some sensory hair cells remain and still work, if they’re not connected to a neuron, then the brain won’t hear the sound,” Oghalai says.

The researchers found that sensory hair cell death occurred immediately after exposure to loud noise and was irreversible. Neuron damage, however, had a delayed onset, opening a window of opportunity for treatment.

A simple solution

The buildup of fluid in the inner ear occurred over a period of a few hours after loud noise exposure and contained high concentrations of potassium. To reverse the effects of the potassium and reduce the fluid buildup, salt- and sugar-based solutions were injected into the middle ear, just through the eardrum, three hours after noise exposure. The researchers found that treatment with these solutions prevented 45–64 percent of neuron loss, suggesting that the treatment may offer a way to preserve hearing function.

The treatment could have several potential applications, Oghalai explains.

“I can envision soldiers carrying a small bottle of this solution with them and using it to prevent hearing damage after exposure to blast pressure from a roadside bomb,” he says. “It might also have potential as a treatment for other diseases of the inner ear that are associated with fluid buildup, such as Meniere’s disease.”

Oghalai and his team plan to conduct further research on the exact sequence of steps between fluid buildup in the inner ear and neuron death, followed by clinical trials of their potential treatment for noise-induced hearing loss.


by Noel Kirkpatrick

There’s a reason a rooster’s crow rouses the farm from a night’s slumber: It can be a very, very loud noise. It’s so loud, in fact, that you have to wonder how roosters don’t lose their hearing.

Which is exactly what researchers from the University of Antwerp and the University of Ghent in Belgium were wondering when they undertook this study in the journal Zoology.

The secret? Roosters can’t really hear themselves cock-a-doodle-doo.

A crow for your ears only

Our ears are delicate. A sound louder than 120 decibels — which is roughly the sound of a chainsaw — can cause permanent hearing loss. The air pressure waves from the noise can, over prolonged exposure, harm or even kill the cells that convert sound waves into the noises our brains can process. At 130 decibels, all it takes is half a second to cause a bit of hearing damage.

Given that roosters can crow at least as loud as 100 decibels, or the decibel level of a jackhammer, you’d expect them to experience some modicum of deafness over the course of their lifetimes. Instead, they continue to hear just fine — and to greet the new day with a blaring hoot.

To figure out just how loud the roosters got, and how they were able to keep their hearing, researchers strapped microphones to the heads of three roosters, with the receiving end pointed at their ears. This was done to measure the sound levels that the roosters themselves would hear when they crowed. The crows were also measured from a distance away. And one other measurement was taken: the researchers performed micro-CT scans on roosters and hens so they could pick apart the geometry of how sounds bounce around in their respective ear canals.

The decibels levels were all over 100 decibels, meaning loud enough to potentially cause damage. One rooster even hit 140 decibels, or the sound level on an aircraft carrier deck, and easily loud enough to cause some damage.

It turns out that roosters keep themselves safe from their own crows with an anatomy adaptation. When they open their beaks to the fullest, a quarter of the ear canal closes and soft tissue covers 50 percent of the eardrum. Basically, they have built-in earplugs that protect them from their own noises. Hens are also protected. Like roosters, the hens’ ear canals also close up, but not as much as their male counterparts’ do.

This built-in protective ability makes sense from an evolutionary perspective. Crowing also serves as a warning to other roosters that this particular group of hens is spoken for — so superlatives rule. The loudest rooster would end up being seen as the most fit to mate with the hens.

A team of researchers led by Dr Alison Bruderer, a postdoctoral fellow at the University of British Columbia, has discovered a direct link between tongue movements of infants and their ability to distinguish speech sounds.

“Until now, research in speech perception development and language acquisition has primarily used the auditory experience as the driving factor. Researchers should actually be looking at babies’ oral-motor movements as well,” said Dr Bruderer, who is the lead author on a study published in the Proceedings of the National Academy of Sciences on October 12, 2015.

In the study, teething toys were placed in the mouths of six-month-old English-learning infants while they listened to speech sounds – two different Hindi ‘d’ sounds that infants at this age can readily distinguish.

When the teethers restricted movements of the tip of the tongue, the infants were unable to distinguish between the two sounds.

But when their tongues were free to move, the babies were able to make the distinction.

“Before infants are able to speak, their articulatory configurations affect the way they perceive speech, suggesting that the speech production system shapes speech perception from early in life,” the scientists said.

“These findings implicate oral-motor movements as more significant to speech perception development and language acquisition than current theories would assume and point to the need for more research.”