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Concussions don't necessarily affect ears — but they can affect the ability to hear

AUDIE CORNISH, HOST:

The symptoms of concussion often include headache, nausea, dizziness and confusion. But researchers say a concussion can also cause an unusual sort of hearing problem. NPR's Jon Hamilton reports.

JON HAMILTON, BYLINE: Tiny nerve cells in the inner ear allow us to detect sounds, but it takes a lot of brainpower to process the signals coming from those cells. Nina Kraus is a neuroscientist at Northwestern University.

NINA KRAUS: Making sense of sound is one of the hardest jobs that we ask our brain to do. So you can imagine that a concussion, getting hit in the head, really does disrupt sound processing.

HAMILTON: Kraus' lab, called Brain Volts, is studying this problem in hundreds of elite college athletes, including football players. And she devotes an entire chapter to concussion in her book "Of Sound Mind: How Our Brain Constructs A Meaningful Sonic World." Kraus says athletes who sustain a concussion usually have normal hearing when it comes to detecting faint sounds, yet they often fail something called the speech and noise test.

KRAUS: You have the athlete listen to a sentence that is embedded in increasingly loud noise.

HAMILTON: A sentence like this.

(CROSSTALK)

UNIDENTIFIED PERSON: Sugar is very sweet.

(CROSSTALK)

UNIDENTIFIED PERSON: Sugar is very sweet.

(CROSSTALK)

UNIDENTIFIED PERSON: Sugar is very sweet.

HAMILTON: Kraus says a concussion may also leave athletes hypersensitive to sounds. To learn more, her lab has been analyzing the electrical signals in areas of the brain that process auditory information.

KRAUS: You just need to put on a couple of scalp electrodes and stick some earbuds in a person's ear and play some sounds.

HAMILTON: That reveals which sound-processing areas in the brain have been affected by a head injury. But researchers are only beginning to understand the problem. Kraus says most athletes recover from a concussion in a week or two. For those with lingering symptoms, she's experimenting with something called rhythm therapy.

KRAUS: The athlete needs to listen to sounds and kind of move their whole body so that they can align their movement with what they're hearing.

HAMILTON: A lot like dancing; the idea is to strengthen the pathways that process sound. The military is also studying the link between head injury and sound processing. Melissa Papesh is a research investigator at the Veterans Affairs National Center for Rehabilitative Auditory Research. She says that during the wars in Iraq and Afghanistan, the VA began to see something odd in military personnel.

MELISSA PAPESH: We have, all of a sudden, this large influx of relatively young and middle-aged people. They're coming into our audiology clinics and saying, hey, I'm having problems hearing. We test their hearing, and their hearing essentially looks normal.

HAMILTON: Their ears are fine, but their brains can't process what they're hearing. Papesh says that like athletes with concussions, they have trouble separating speech from background noise. And she says they often have another symptom.

PAPESH: They have problems processing rapidly spoken speech. Even the rate that I'm speaking right now might be too rapid for some of these folks to actually process the information.

HAMILTON: The scientists knew that the blast wave from a roadside bomb could cause a concussion, so Papesh says they took a closer look at the patients who had trouble processing sounds.

PAPESH: And when we started looking into some of those cases, it definitely seemed like brain injury and, in particular, blast exposure was really the main thing that was linking those things together.

HAMILTON: Some veterans still have symptoms more than a decade after being exposed to a bomb blast, and Papesh says researchers are trying to figure out whether exposure to lots of smaller blast waves can also affect certain military personnel.

PAPESH: So these are folks who fire shoulder-mounted weapons, or they are folks who are using explosive munitions to try to break through doors.

HAMILTON: This sort of exposure is especially troubling because it can occur during training as well as in combat.

Jon Hamilton, NPR News.

(SOUNDBITE OF CASPIAN'S "DUST AND DISQUIET") Transcript provided by NPR, Copyright NPR.