The brain may not be able to make sense of sounds after a concussion
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Concussion symptoms include headaches, nausea, dizziness and confusion. Researchers say that a head injury can make it difficult to hear speech in noisy rooms.
Nina Kraus, a Northwestern University professor of neurobiology, says that making sense of sound is one the most difficult jobs our brains have to do. You can see that a concussion (a head injury) can disrupt sound processing.
Kraus estimates that between 15% and 20% of concussions can cause persistent sound processing difficulties. This means that thousands of Americans are affected every year. This problem is more prevalent in the military where many troops were exposed to roadside bombs.
From ear to head
Kraus states that sound perception begins with inner ear nerve cells, which convert pressure waves into electrical signals. It takes a lot brain power to convert those signals into the auditory environment we perceive.
To determine the source of sound, the brain must compare signals from both ears. It then needs to track changes in volume, pitch and timing, among other characteristics.
Brainvolts is Kraus's laboratory and it is currently conducting a five year study on 500 college athletes. The goal of the study is to determine how concussions can impact the brain's ability process the vast amount of auditory information it receives. In her 2021 book Of Sound Mind: The Way Our Brain Constructs Meaningful Sonic World, Kraus devotes an entire chapter on concussion.
Kraus states that college athletes who have sustained a concussion typically have normal hearing, at least in the sense of detecting faint sounds. They often fail the "speech-in-noise" test.
She says, "You ask the athlete to listen to a sentence embedded in increasing loud noise." Normal brain function will allow people to understand the sentence even if there is lots of background noise. Many people who have suffered a concussion may fail to pass the test.
Concussions can also cause athletes to be hypersensitive to sounds.
Kraus's laboratory has been studying the electrical signals within the brains that process auditory information.
She says that all you need is a few scalp electrodes, some earbuds, and some sound effects.
This method can show which brain sound-processing areas have been affected by head injuries, even if the individual being tested is asleep. Kraus states, "This allows you to assess brain health objectively."
She says that researchers are just beginning to understand the brain damage caused by a concussion. Early evidence indicates that brain injuries can cause "bottlenecks", which prevent information from flowing rapidly from one brain area to the next.
Kraus states that most athletes can recover from a concussion within a week to two weeks. She's exploring rhythm therapy for those who have lingering symptoms. It is a form of dance-based therapy.
She says, "Athletes need to be able to hear sounds and move their whole body in alignment with what they are hearing." This is done to improve the sound processing pathways.
Bomb blasts can cause concussion
Melissa Papesh is a researcher at the Veterans Affairs National Center For Rehabilitative Auditory Research in Portland, Ore. Melissa says that the military has been researching the relationship between sound processing and head injury since 2005.
She says that the VA noticed something unusual in military personnel during the wars of Afghanistan and Iraq.
She says, "We have all of sudden this large inflow of relatively young people and middle-aged people." "They come into our audiology clinics saying, "hey, I have problems hearing."
Their hearing is "essentially normal" except for when Papesh tests it. Surprisingly their ears work perfectly. Their brains are unable to process the information they hear.
These patients, like athletes who have suffered concussions from head injuries, struggle to distinguish speech from background noise. She says that many have difficulty processing fast spoken speech.
VA scientists realized that a roadside bomb blast could cause a concussion, without any visible signs of injury. They looked closely at patients with difficulty processing sounds and discovered that many of them had been exposed to at least one blast.
Papesh states that some veterans have auditory symptoms for more than a decade even after being exposed to a bomb blast.
The VA is now looking into another possible source of brain injury after most military personnel have been removed from combat. This involves being exposed to small blast waves that travel through the brains and skulls of those who use high-powered explosives or fire high-powered weapons in training exercises.
"That will be a large area of research in future," Papesh states. The military wants to stop this stuff from becoming a problem for veterans.