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Tinnitus

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Tinnitus

Tinnitus is a perception of sound where no external source is present. Tinnitus is often described as a ringing, buzzing, or humming sensation in the ear(s) or head region. Tinnitus is a symptom, not a disease. Almost all tinnitus is associated with a disturbance in the auditory system – either within the ears or the nerves that carry signals from the inner ear to the hearing parts of the brain. Most patients with tinnitus do not have an active disease or pathology but rather damage or dysfunction within the inner ear that is most commonly associated with exposure to high levels of sound or simply due to the aging process. The term tinnitus comes from the Latin verb tinnire meaning “a jingling”. It is commonly described as a phantom perception of sound where a person hears a sound in their ears while there is no actual sound present in the environment.

What is interesting about tinnitus is that only a small proportion of people who experience the symptom are actually bothered by it. It is therefore important to distinguish between simple awareness of tinnitus versus the significant distress that this awareness sometimes produces. Tinnitus is really much more than just a perceived sound though. It can be strikingly similar to the “feel” you get when someone scratches their fingernails across a chalkboard.  There are two correct ways of pronouncing the word tinnitus. The preferred way, often heard in the medical community, is tin’-it-us with emphasis on the first syllable. Alternatively, it may be pronounced tin-i’-tus with emphasis on the middle syllable, which is also acceptable.

Most if not all people will at some point in their lives experience a temporary ringing sensation in their ears. It is usually abrupt and lasts for several seconds and then fades away. Hearing may be muffled during this time. Scientists consider the idea that tinnitus-like sensations are always present just below the level of awareness in almost everyone, probably due to the healthy random firing of the auditory nerve at rest. People are prevented from constantly hearing these sounds because of filtering networks in the brain that treat them as unimportant and reject them through a process known as habituation. Sometimes the filtering network lets an occasional sound slip through, making us briefly aware of a sound sensation. Increased activity in the emotional brain (limbic system) can also open up these filters. The precise scientific understanding of its cause is not known but there is general agreement that it is a normal auditory experience and there is no reason for concern. 

Tinnitus Prevalence and Risk Factors  

Tinnitus symptoms are actually quite prevalent. Approximately 50 million Americans have tinnitus to some degree. It is estimated that 17% of adults, 33% of the elderly and 13% of children have tinnitus. Tinnitus perception is considered a central deficit in the cancellation of meaningless signals in the auditory pathways. The causes of tinnitus are often due to multiple sources. Two or more factors may synergistically lead to tinnitus becoming symptomatic. People with tinnitus often have sleep problems, poor concentration, anger, irritation, guilt, fear, anxiety, and depression.  Known risk factors for tinnitus are hearing loss, exposure to loud sound, hypertension, anxiety or depression, and post-traumatic stress disorder. Acoustic trauma kills hair cells in the cochlea and neurons in the acoustic nerve and the dorsal cochlear nucleus. The automatic repair process known as neural plasticity is postulated as the main cause of chronic tinnitus. Protecting the ears from loud noises is clearly one of the best ways to prevent tinnitus. Remember, hearing loss due to noise exposure is painless, permanent, and progressive.

While not everyone with tinnitus has hearing loss, for those that do the hearing loss plays a large role in tinnitus perception. It is proposed that hearing loss can cause the filtering networks to malfunction. The hearing loss reduces the amount of ambient sound entering the auditory pathways. This causes the filters to open wider to let more information through. Ultimately awareness is created of our neurological noise floor that everyday sounds would otherwise typically mask or block from our perception. The neurological activity becomes more noticeable, especially as the brain also tends to increase the sensitivity in the auditory system to compensate for the reduced auditory input. Deprivation of sound to the nervous system (hearing loss) is the strongest factor that can activate neural plasticity and cause hyperactivity in the auditory system. Plasticity is what allows the nervous system to change its function in various ways, typically for learning or self-repair. Tinnitus becomes a side effect of benign compensation occurring within the auditory system. In chronic tinnitus, the initial tinnitus signal is recognized and evaluated as important by the brain because of its continuous presence.

Between the ear and the brain are 2 million nerve cells that form a neuronal network, capable of sophisticated pattern recognition, enhancement, and suppression of auditory signals. The neuronal networks become highly tuned to the tinnitus pattern so that the auditory system can easily recognize it even in the presence of other signals. This is the same as our ability to hear the sound of our own name even in high levels of competing background noise. Signals that are considered highly significant to the brain are new signals, those that are associated with emotional or unpleasant situations, related to survival, and those that are a threat to health or life. If the first experience of tinnitus evokes a high level of annoyance or anxiety or is associated with something unpleasant or occurs during a period of stress or anxiety, it is classified as important and this will result in an enhancement of activity in the limbic system and/or autonomic nervous systems. This prepares a person for a defensive action. These systems remain on an increased level of activity for a prolonged period of time. The tinnitus signal is extensively monitored which further enhances its importance. The neuronal networks become even more highly tuned to the tinnitus signal. Even in mild cases of persistent tinnitus, a conditioned response is set up to the tinnitus sound. This conditioned response is part of the subconscious brain and therefore automatic and cannot be consciously turned off.

Distressing tinnitus is mostly due to a person’s reaction to hearing the tinnitus, rather than just due to the presence of tinnitus itself. When tinnitus is first heard a person may become concerned that it is a danger signal warning of something wrong internally. Some try to control the tinnitus through changes in diet – taking vitamins, reducing or eliminating caffeine intake, or by altering their lifestyle. Some seek out quiet places hoping the tinnitus will go away. These attempts to deal with tinnitus are usually not helpful. The more a person tries to control the tinnitus the louder it seems to get.  Non-distressing tinnitus occurs when a sound is judged by the brain to be of no particular importance and produces little activation of the limbic and autonomic nervous systems. With repetitive appearance of this particular sound, the subcortical pathways will block it, and there will be no awareness of the sound. The brain is capable of filtering out continuous background and non-threatening inputs from the senses. This is the process of habituation. The perception of a tinnitus sound can be habituated as long as it does not provoke an emotional response. When this happens, the brain reclassifies tinnitus into the category of a neutral signal. Habituation is not a cure for tinnitus. Tinnitus can still be heard when attention is directed towards it, but there is no reaction to the tinnitus and overall awareness is greatly reduced.

Category
Tinnitus
Created
Wednesday, 29 April 2015
Group Admin
Dr. Rohe | Tinnitus and Hearing Center of Arizona
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