Overactive nerves in head and neck may account for 'ringing in the ears'

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Overactive nerves in head and neck may account for 'ringing in the

ears'

Results in animals suggest that acupuncture and trigger point

therapy may be effective treatments for people plagued by tinnitus

http://www.eurekalert.org/pub_releases/2008-01/uomh-oni011008.php

Do your ears ring after a loud concert " Nerves that sense touch in

your face and neck may be behind the racket in your brain,

University of Michigan researchers say.

Touch-sensing nerve cells step up their activity in the brain after

hearing cells are damaged, a study by U-M Kresge Hearing Research

Institute scientists shows. Hyperactivity of these touch-sensing

neurons likely plays an important role in tinnitus, often

called " ringing in the ears. " The study, now online in the European

Journal of Neuroscience, will appear in the journal's first January

issue.

The research findings were made in animals, but they suggest that

available treatments such as acupuncture, if used to target nerves

in the head and neck, may provide relief for some people plagued by

tinnitus, says E. Shore, Ph.D., lead author of the study and

research professor in the Department of Otolaryngology and the

Kresge Hearing Research Institute at the U-M Medical School.

People with tinnitus sense ringing or other sounds in their ears or

head when there is no outside source. Whether it's mild and

intermittent or chronic and severe, tinnitus affects about one in 10

people. An estimated 13 million people in Western Europe and the

United States seek medical advice for it. It is a growing problem

for war veterans. Since 2000, the number of veterans receiving

service-connected disability for tinnitus has increased by at least

18 percent each year, according to the American Tinnitus

Association.

Increasing numbers of baby boomers are also finding that when they

can't hear as well as they used to, tinnitus seems to move in. The

condition commonly occurs with hearing loss, but also after head or

neck trauma such as whiplash or dental work.

Tinnitus varies in individuals from a faint, high-pitched tone to

whooshing ocean waves to annoying cricket-like chirping or

screeching brakes. For some, it is constant and debilitating.

Some people, oddly enough, find that if they clench the jaw or press

on the face or neck, they can temporarily stop tinnitus, or in some

cases bring it on. To understand tinnitus and its strange link to

touch sensations, Shore and her research team have conducted a

series of studies in guinea pigs, measuring nerve activity in a part

of the brain called the dorsal cochlear nucleus that processes

auditory and other signals.

In normal hearing, the dorsal cochlear nucleus is the first stop in

the brain for sound signals arriving from the ear via the auditory

nerve. It's also a hub where " multitasking " neurons process sensory

signals from other parts of the brain.

" In this study, we showed that when there is a hearing loss, other

parts of the brain that normally convey signals to the cochlear

nucleus have an enhanced effect, " says Shore, who is also an

associate professor in the Department of Molecular and Integrative

Physiology at the U-M Medical School.

" When you take one source of excitation away, another source comes

in to make up for it. The somatosensory system is coming in, but may

overcompensate and help cause tinnitis, " she says.

The somatosensory system is a nerve network in the body that

provides information to the brain about touch, vibration, skin

temperature and pain. The part of the system that provides

sensations from the face and head, called the trigeminal system,

brings signals to the cochlear nucleus that help us hear and speak.

But when people experience hearing loss or some other event, such as

having a cavity filled or a tooth implanted, these neurons from the

face and head can respond like overly helpful relatives in a family

crisis. The resulting neuron firings in the cochlear nucleus, like

too many phone calls, create the din of tinnitus, a " phantom sound "

produced in the brain.

In the study, Shore and the paper's second author Seth Koehler, a U-

M Ph.D. student in the U-M departments of Otolaryngology and

Biomedical Engineering measured the patterns of activity of neurons

in the brains of normal and deafened guinea pigs. They used a 16-

electrode array to measure signals from the trigeminal nerve and

multisensory neurons in the dorsal cochlear nucleus. When they

compared results in the two groups, they found clear differences in

trigeminal nerve activity.

" The study shows that in deafened animals, the somatosensory

response is much stronger than in animals with normal hearing, "

Shore says.

Shore's research team knew from earlier research that some neurons

in the cochlear nucleus become hyperactive after hearing damage, and

this hyperactivity has been linked to tinnitus in animals.

" This study shows that it is only those neurons that receive

somatosensory input that become hyperactive, " she says, which should

make the search for treatments for tinnitus in some people more

straightforward.

Many people with temporomandibular joint syndrome (TMJ), a condition

that causes frequent pain in the jaw, experience tinnitus. Shore's

research could lead to a better understanding of this link. In

people with TMJ, the somatosensory system is disrupted and inflamed.

Shore says that it's possible that in this situation, as in hearing

loss, somatosensory neurons stir excessive neuron activity in the

cochlear nucleus.