|Tinnitus is a common phenomenon
that affects about 17% of
the general population and about 33% of the elderly. Until recently tinnitus
did not receive sufficient attention, both in clinical practice and in research.
While the perception of tinnitus is very real, there is no external sound
corresponding to the patients' perception of sound; thus, tinnitus can be
classified as a phantom auditory perception. Consequently there is no objective
measurement of tinnitus.
Much effort has been committed to the psychoacoustical description of tinnitus, such as: its pitch, loudness, whether it is perceived in one ear, both ears, or in the head, the minimal level of noise needed to suppress its perception, "how it sounds," etc. The expectation was that these measurements would establish different categories of tinnitus, where for each category a specific treatment could be applied with a predictable outcome. This expectation has not been fulfilled, but nevertheless the efforts have provided interesting, while counterintuitive, results. One important result was that the psychoacoustical characterization of tinnitus has basically no relation to the level of annoyance evoked by tinnitus. In other words, two people with a very similar psychoacoustical description of tinnitus can differ dramatically in their level of annoyance induced by tinnitus: One person ignores tinnitus and is not aware of it and is not annoyed at all, while the other person is constantly aware of tinnitus and has difficulty focusing their attention on work, falling asleep, and enjoying life.
Approximately 75% of all the people who experience tinnitus are not bothered by it, and they treat tinnitus like any other sound to which they easily habituate. The important aspect is that there is no difference in the psychoacoustical characterization of tinnitus between those who experience tinnitus and those who suffer because of it. This observation is one of the findings responsible for the development of a new model of tinnitus, and based on the model, Tinnitus Retraining Therapy. The model is based on basic, well-established neurophysiological and psychological principles. Mainly:
The following scenario of the emergence of tinnitus perception has been proposed (Neurosci.Res. 8:221-254, 1990). A weak imbalance of neuronal activity within the auditory system, most frequently related to damage of the inner ear, is detected at low levels in the auditory system, and being a new signal it is further enhanced by subcortical centers, transferred to the auditory cortex and perceived as a sound - tinnitus, and is subsequently evaluated. In the majority of cases the continued presence of tinnitus combined with a lack of any positive or negative association results in habituation of the reaction to the tinnitus signal. Although tinnitus perception may still be possible, there is little or no annoyance or discomfort. This situation is typical for children, or those leaving a loud concert, who tend to treat tinnitus as a natural event, and tinnitus typically does not annoy them.
However, in some cases, the perception of tinnitus is associated with a negative emotion. Patients treat tinnitus as an indicator that something is wrong with their hearing, or their brain, and as a result they start to focus their attention on the tinnitus. Quite frequently this occurs as a result of "negative counseling." All too often helthcare professionals advise patients to check for a brain tumor, or indicate that the tinnitus is basically a psychiatric condition, or tell the patient "nothing can be done with tinnitus" and that the patient has to "learn to live with it." This negative reinforcement of tinnitus perception actually enhances the initial responses of the autonomic nervous system evoked by fear. As tinnitus is commonly continuously present and evokes a strong emotional response, this results in the tuning of the neuronal networks detecting the tinnitus signal itself. Consequently, this increases the time an individual is aware of the tinnitus and further enhances the aversive emotional responses and the reaction of the autonomic nervous system, thus increasing annoyance. Notably, the involvement of the limbic and autonomic nervous systems is responsible for the annoyance evoked by tinnitus; the loudness and pitch of tinnitus are irrelevant to a large degree and normally do not play a significant role.
For a significant proportion of patients the compensatory action of the auditory system results in the emergence of hyperacusis. Research on animals has revealed that after permanent or temporary hearing loss the increased sensitivity of about 25% of the neurons in the subcortical auditory centers. These data are in agreement with human data which showed that if a person is put in a chamber with a very low sound level, the sensitivity of hearing increases, all sounds starts to sound loud, and 94% of the people develop temporary tinnitus. These data indicate that tinnitus can result from enhanced sensitivity of the auditory system, which in turn may lower the maximum sound level that person finds comfortable. For these patients, tinnitus and hyperacusis are two manifestations of the same internal problem. In practice the contribution of the hyperacusis component to tinnitus ranges from none at all to the situation where hyperacusis is the only or dominant problem.
From the patient's point of view the crucial question is what can be done to remove tinnitus-evoked annoyance. To our knowledge there is no drug, procedure, or surgery that can eliminate the source of tinnitus without profound side effects. As evident from the model, even in cases with significant inner ear contribution, attempts to solve the problem by destroying the cochlea or the auditory nerve would not be consistently helpful while making the patient deaf. To make the situation worse, it has been shown that cutting the auditory nerve, which is still promoted by some as a treatment for tinnitus, actually causes tinnitus in close to 60% of the people who did not experience tinnitus before the operation. Another problem arises from the observation that quite frequently more than one type of tinnitus coexists and therefore we would need to attenuate all various sources of tinnitus.
The Tinnitus Retraining Therapy, which was developed by Dr. Jastreboff in mid '80s and published in 1990 (Jastreboff, P.J. Phantom auditory perception (tinnitus): mechanisms of generation and perception. Neurosci.Res. 8:221-254, 1990), offers a potential solution to this problem. If we cannot erase the source(s) of tinnitus we should turn our attention to what is happening between the source of tinnitus (most frequently at the periphery) and the level where tinnitus is perceived -- the cerebral cortex. The idea is to block tinnitus-related neuronal activity from reaching the level of the cortex where it is perceived, and from activating the limbic and autonomic nervous systems -- to habituate tinnitus perception and tinnitus-induced reactions.
Everyday experience and research show that we are consciously aware of only a small portion of incoming sounds. Although other sounds evoke changes in the neuronal activity within the auditory pathways, this activity is filtered out by the neuronal networks before they reach the level of conscious perception. Similarly, most sounds do not evoke any emotional reaction or activate the autonomic nervous system.
To understand how tinnitus emerges, it is helpful to understand how sound is processed in the auditory pathways. In the absence of sound there are high levels of neuronal activity in the auditory nerve, as well as in other neurons in the auditory pathways, but this activity is random. The nervous system filters out this activity and therefore we do not perceive it as sound. This random activity can be considered as "a code for silence."
When we are exposed to a sound the activity within the auditory system increases, and becomes more regular and synchronized. While the patterns of electrical activity within the auditory nerve closely reflect the sound that reaches our ear, this activity undergoes extensive processing in several subcortical centers within the auditory pathways before reaching the cortex, where perception of the sound occurs.
Of consequence is the observation that this processing of information can itself result in changes of the connections within the brain that are involved in transmitting signals from the ear to the cortex. In other words, repeated activation by a sound not associated with anything of significance will result in decreased activation of the cortical and limbic areas, whereas sound associated with a significant event, particularly related to danger, will be enhanced and will strongly activate the cortical areas and emotional response. Our brain sorts sounds according to their significance, giving important sounds high priority to our attention and filtering out (habituating) insignificant sounds. Notably, the rules controlling sorting are changing all our life, and with proper training we can enhance our perception of some sounds, while we can train our brain to filter out other sounds.
Accordingly, if we can train the brain to classify tinnitus-related neuronal activity as representing a neutral, nonsignificant signal, then the process of habituation will occur automatically. To achieve this, it is necessary, however, to fulfill two basic conditions:
The first condition results from the observation that signals that induce fear, indicate danger, or that are associated with any unpleasant situation cannot be habituated. To avoid unpleasant situations we must not habituate sounds that provide warning! The decreased negative association of tinnitus is achieved through directive counseling, with emphasis on teaching the patient the basic function of the auditory system and the brain in relevance to tinnitus. This is performed because a known danger evokes a weaker reaction of the autonomic system than an unknown danger. As it is argued in the listed papers, the reactions of the autonomic nervous system are responsible for tinnitus annoyance and decreasing these reactions is a primary goal of the therapy.
The second condition is less obvious, but equally important. For retraining the neuronal networks involved in processing the tinnitus signal, it is fundamental that tinnitus-related activity can be detected. We cannot, by definition, achieve retraining on something that cannot be detected! Thus, for habituation-oriented therapy "masking" of tinnitus is counterproductive. Indeed, preliminary results of a study presently conducted on patients who used masking for 10ª15 years fully confirm this statement. In these patients tinnitus and its annoyance did not change in all these years. Once they were switched to a habituation©oriented therapy, they achieved tinnitus habituation within a year.
Low level, broad band sound is used to facilitate tinnitus habituation. It was mentioned previously that 94% of the people placed in a very quiet environment develop temporary tinnitus. Silence actually enhances tinnitus and hyperacusis. All our patients are advised to avoid silence and immerse themselves in a low level, emotionally neutral sound environment. The sound used in Tinnitus Retraining Therapy can be of various origins, but for both theoretical and practical reasons we are using broad band noise generated by devices which are worn behind the ear.
The process of retraining takes 12 to 18 months. However, once tinnitus habituation is achieved there is no need for continuing the treatment. Another important property of Tinnitus Retraining Therapy is that it cannot create any harm. At the moment we have over 800 patients treated at our Center, and the results from evaluating a random sample of 150 patients showed over 80% of significant improvement (Jastreboff, P.J., Gray, W.C., Gold, S.L. Neurophysiological approach to tinnitus patients. Am.J.Otology, 17:236-240, 1996).
|Last updated May 27, 1998|
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