Research scientists at Northwestern University have discovered that ears have a special pain pathway that serves as a warning system, sending signals to the brain to help protect us against damaging noise. According to an article published online in the January 29, 2015 edition of Current Biology, there may be more than one nerve pathway in our ears that deliver sound signals. One pathway, they say, prompts us to cover our ears in response to blaring noises from sirens and firecrackers. Less dramatic noises, the scientists have discovered, may travel along a different nerve pathway, without triggering the same protective response.
The Northwestern University scientists report that their discovery of this second nerve pathway to the inner ear, which sends nerve signals from the cochlea to the brain, may provide insight into the cause of such challenging hearing conditions as tinnitus, or hyperacusis, an oversensitivity and earache in response to everyday sounds. Hyperacusis is said to be common in soldiers exposed to explosives in the military.
The second pathway in the ear, which the scientists named auditory nociception (pain), is different from the one that transfers information about normal-level sounds to the brain and enables you to hear things like conversation or soft music. This second pathway, they say, is populated by a single set of neurons activated only by dangerous levels of noise. Scientists aren’t sure if the neurons are triggered by the death of hair cells (sensory cells in the inner ear) or by dangerous sound levels.
“It’s very important for your system to have protection from damaging sound,” said senior author Jaime García-Añoveros, PhD, associate professor of anesthesiology at Northwestern University’s Feinberg School of Medicine. “When sensory hair cells in the ear die, they are not repopulated. That’s why hearing loss is irreversible. You need to be able to detect dangerous sound the way your nerve cells alert you to the danger of putting your hand on a hot iron.”
Dr García-Añoveros reports that the study of the hearing nerve pathway was conducted using mice, but he believes there may be an equivalent pathway in humans, which he and the research team hope to investigate as a next step. The current study will be highlighted in another article slated to appear in the February 20, 2015 edition of Nature Reviews Neuroscience.
Source: Northwestern University
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