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The meaning of tinnitus sounds
In 1953 Heller and Bergman performed an
simple and classic experiment. They placed 80 tinnitus free individuals
(university members) in a sound proofed room for 5 minutes each, asking them to
report on any sounds that might be heard. The subjects thought they might be
undergoing a hearing test, but actually experienced 5 minutes of total silence.
93% reported hearing buzzing, pulsing, whistling sounds in the head or ears identical
to those reported by tinnitus sufferers.
This simple experiment shows almost anyone can detect background
electrical activity present in every living nerve cell in the hearing pathways
as a sound. Although some areas of the auditory system may be more active than
others, every neurone will contribute to some extent to the final
perception of tinnitus. These electrical signals are not evidence of damage, but
compensatory activity that occurs all the time in the auditory system of each
one of us. Compensation can occur
as a response to changes in our sound environment (e.g. silence) to hearing loss
which may be a natural part of ageing, or to exposure to sudden noise.
Its good to think of the sounds produced by this compensatory activity as
'the music of the brain'. Of
those who DO experience persistent tinnitus, population studies have shown
that about 85% do not find it intrusive, disturbing or anxiety provoking
(something tinnitus sufferers find very hard to believe!). The reason for
this is not so much because the quality or loudness of the tinnitus is
different; in fact we have found that tinnitus is of a very similar type of
sound in those who are bothered by it and those who are not.
The main difference is that those who find
tinnitus troublesome, evaluate and perceive it as a threat, or an annoyance,
rather than something of little or no consequence. Tinnitus may also emerge for the
first time when something else unpleasant or frightening is happening to us.
In these situations, tinnitus is classified as a warning signal, relating
either to an bad experience (classical Pavlovian conditioning) or to negative
thoughts about its meaning or outcome. Just
as an animal is alerted to danger by the sound of a predator, and focuses solely on
that sound in order to survive, so those who consider that tinnitus is a threat
or warning signal are unable to do anything but listen to it. It is part of the
mechanism that all animals have developed for self preservation, although
clearly in this situation it is not working to our advantage! Many people
complain of the loss of silence, something they previously greatly treasured and
enjoyed, before tinnitus became
Persistent tinnitus depends on a
conditioned response
What happens, even in mild cases of
persistent tinnitus, is that a conditioned response (reaction) is set up to the
tinnitus sound. As the conditioned
response is part of the subconscious brain, and automatic, what you may be
thinking about tinnitus at any time, (or even if you're not thinking about it),
is irrelevant to the reaction produced. Moreover, it is the reaction to
tinnitus, which is creating distress, not the tinnitus itself (another difficult
concept for some). The degree to
which unpleasant feelings about tinnitus (from the limbic system) and increased
tension (from autonomic system stimulation) are experienced, dictates the
severity of the tinnitus . The
loudness and quality of the sound heard is irrelevant. This mechanism is
illustrated best by the Jastreboff model in a graphical format (figure
4).
Figure 4
The Jastreboff Neurophysiological Model of Tinnitus
1990
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