A Step Forward in Understanding Hyperacusis with Pain

A recent study identified a second pathway from the ear to the brain. Getty Images BSIP/UIG

A recent study published in the journal Current Biology created a lot of buzz in the Audiology community. Scientists at Northwestern University and the Eaton-Peabody Laboratory at Harvard discovered a novel pathway from the ear to the brain in mice that transmit information about sound levels that are loud enough to damage the ear.

M. Charles Liberman, Ph.D, who is the director of Eaton-Peabody Laboratories in the Massachusetts Eye and Ear Infirmary and Vice Chair of Basic Research in the Department of Otolaryngology at Harvard Medical School was kind enough to discuss this research with about.com.


He cautions this pathway is still not completely proven, but it’s taken a “big step beyond speculation with the publication of this latest paper.” There are two kinds of sensory cells in the cochlea; sensory cells are responsible for turning the vibrations that sound produces into electrical activity. The first type, the Outer Hair Cells (OHC), are like biological motors that help amplify sound vibrations and are the reason we are able to hear incredibly faint sounds. The other type,  the Inner Hair Cells (IHC)  are more like sensors that respond to the vibrations and send the information to the brain. There are also two very different kinds of nerve fibers; one kind of nerve fiber that connects the IHC to the brain and one kind that connects the OHC to the brain.

The nerve fibers that connect the IHC to the brain are large and heavily myelinated; this allows for rapid transmission of information.

The OHC fibers are thin and do not have myelin. These fiber types are seen in other parts of the body, such as our skin. The large fibers conduct information about touch while the thin fibers carry information about pain.

What does this mean?

This could be a very important step forward in finding treatment options for people who suffer from hyperacusis with pain.

Hyperacusis with pain has been described by patients as a burning sensation in their ears, “like molten lead being poured in the ears” and the pain can last for days following exposure to noise. This condition is much different than sound sensitivity, phonophobia, misophonia, or loudness hyperacusis (in which discomfort stops when the sound stops). It is unknown why some people develop this type of hyperacusis.

Dr. Liberman likens this to pain/touch pathways – if you were to touch your hand and remove that touch, the sensation ends. If you cut the hand with a knife, the pain will persist for several days. Pain fibers act differently than touch fibers. Current treatments for loudness hyperacusis (such as tinnitus retraining therapy, which works to change the brain’s reaction to the sound) are not effective for hyperacusis with pain.

The good news is this study shows that the neurotransmitters and receptors in OHC and IHC nerve pathways are different; which opens the way for specific drug treatments to target this pathway without impacting hearing ability.

When asked about future treatments, Dr. Liberman hopes to see the development of more specific pharmaceutical agents that can block pain fibers and be administered to the cochlea through the eardrum; it is routinely do-able as an outpatient procedure with relatively low risk.

He imagines a day when patients with hyperacusis with pain can have a procedure in the office that treats this debilitating condition.


Liberman, M. Charles. Personal interview.  05/13/2015.

Flores E, et al. “A Non-canonical Pathway from the Cochlea to Brain Signals Tissue-Damaging Noise.” Current Biology 25 (2015) 606-612. Print.

Cohen, Joyce. “When Everyday Noise in Unbearable.” The New York Times (12/1/2014). Accessed from http://well.blogs.nytimes.com/2014/12/01/when-everyday-noise-is-unbearable/

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