Hearing is a series of events in which sound waves in the air
produce electrical signals and cause nerve impulses to be sent to the
brain where they are interpreted as sound. The ear has three main
parts: the outer, middle and inner ear. Sound waves enter through the
outer ear and reach the middle ear where they cause the ear drum to
vibrate. The vibrations are transmitted through three tiny bones in the
middle ear, called the ossicles. These three bones are named the
malleus, incus and stapes (and are also known as the hammer, anvil and
stirrup). The ear drum and ossicles amplify the vibrations and carry
them to the inner ear. The stirrup transmits the amplified vibrations
through the oval window and into the fluid that fills the inner ear.
The vibrations move through fluid in the snail-shaped hearing part of
the inner ear (cochlea) that contains the hair cells. The fluid in the
cochlea moves the top portion of the hair cells, called the hair
bundle, which initiates the changes that lead to the production of the
nerve impulses. These nerve impulses are carried to the brain where
they are interpreted as sound. Different sounds move to the population
of hair cells in different ways, thus allowing the brain to distinguish
among various sounds.
For the first time, scientists (Alan H. Lockwood, M.D., of the State University of New
York in Buffalo) have located an area in the brain involved in the production of tinnitus.
Tinnitus is a ringing, roaring, buzzing, or clicking sound that occurs inside the head,
it is often referred to as "ringing in the ears." The noise can be intermittent or
constant, with single or multiple tones; it can be subtle or at a life-shattering level.
It can strike people of all ages and, for most, it is difficult to treat.
There are currently over 50 million Americans who are affected by tinnitus to some
degree. Of these, about 12 million suffer severely enough to seek medical attention. And,
about one million sufferers are so seriously debilitated that they cannot function on a
"normal," day-to-day basis.
Using positron-emission tomography (PET), Dr. Lockwood's group was able to map brain
regions of individuals who had tinnitus in only one ear. These individuals also had the
ability to change the loudness of their tinnitus by performing special movements of their
face and mouth. Cerebral blood flow, an indication of increased brain activity, was
measured while these individuals were at rest, and performed the movements that affected
their tinnitus, and while listening to loud beeps or pure tones that were presented using
ear phones. The PET scan detected changes in the auditory cortex, that part of the brain
that processes sounds, on the side of the brain opposite the tinnitus. In contrast, the
auditory cortex on both sides of the brain reacted to pure tones presented to one ear at a
time. Since external tones presented to one ear affect both sides of the brain, the fact
that the internal tones of tinnitus affect only one side of brain indicate that tinnitus
may be initiated by brain activity rather than by the ear.
Having the ability to image brain activity patterns during various communication events
involving stuttering, aphasia, tinnitus, and American Sign Language is revolutionizing our
understanding of normal and disordered processes of human communication. In one of many
remarkable advances this year, NIDCD scientists are able to visualize brain activity
occurring with tinnitus, or ringing in the ears. Tinnitus has been extremely difficult to
study without an objective model as it is associated with virtually every kind of hearing
loss. These studies provide ground-breaking information about the nature of tinnitus,
which will hopefully lead to improved strategies for diagnosis and treatment for the
millions of Americans challenged with the incessant or intermittent audiotory sensation
that is tinnitus.
While not every case of tinnitus has an apparent source, there are a variety of causes.
Exposure to loud noise, either over an extended period of time or one extreme incident, is
probably the most common. Other possible causes of tinnitus include: certain medical
conditions; certain medications; allergies.
Exposure to harmful sounds causes damage to the sensitive hair cells of the inner ear
and to the nerve of hearing. These structures can be injured by noise in two different
ways: from an intense brief impulse, such as an explosion, or from continuous exposure to
noise, such as that in a woodworking shop.
The effect from impulse sound can be instantaneous and can result in an immediate
hearing loss that may be permanent. The structures of the inner ear may be severely
damaged. This kind of hearing loss may be accompanied by tinnitus, which may subside over
time. Hearing loss and tinnitus may be experienced in one or both ears, and tinnitus may
continue constantly or intermittently throughout a lifetime.
There is not a cure for tinnitus. However, a variety of treatment options exist that
offer varying levels of relief to many sufferers. Treatment options include:
- biofeedback
- hearing aids
- medication
- masking
- Tinnitus Retraining Therapy
- TMJ treatment
Be sure to consult with a qualified healthcare professional who treats tinnitus for
more information about these and other treatment options.
