Tinnitus is often described as buzzing, ringing, hissing, humming, roaring, or whistling that someone hears in the absence of any external sound. More than 50 million people in the United States alone suffer from the condition, according to the American Tinnitus Association.
Usually brought on by exposure to loud noise, the problem is especially significant in the military, with more than 34 percent of returning veterans from Iraq and Afghanistan suffering from the condition.
Neurological Basis of Tinnitus
There are many potential causes for tinnitus and it is likely that no one explanation will cover all cases. Nevertheless, it is generally accepted that tinnitus involves a series of neurological changes within the auditory system as well as systems in the brain that influence attention and emotional state1.
The tinnitus perception itself is a result of changes in the auditory system that lead to increased and altered activity in the neurons of the auditory system. This altered activity is interpreted by the brain as sound. Many people experience the perception of sound in this way – but are not especially bothered by it.
For those people who experience bothersome tinnitus, the disturbance associated with tinnitus and its impact on their quality of life is primarily the result of the reaction to this perception, rather than the perception itself. This reaction involves further changes in the parts of the brain that control conscious attention and one’s emotional state, such as the limbic and autonomic nervous systems.
Role of hearing loss in triggering tinnitus
Tinnitus is usually triggered by some disruption to the auditory system. Typically, this involves some form of hearing loss, which may be the result of aging, exposure to loud noises, certain drugs and medications, middle ear infections, or other causes. Regardless of the hearing loss cause, and whether it is permanent or temporary, it can lead to the changes in the activity of neurons in the auditory system – which the auditory cortex then interprets as sound.
Other tinnitus triggers
Although these other causes contribute to only a small percentage of tinnitus cases, their existence underlines the need for a thorough head, ear, nose and throat examination. Appropriate referral to an otolaryngologist or prosthodontist may also be appropriate.
Drugs2 – Some that have been implicated in hearing damage and tinnitus include:
- Loop diuretics
- Chemotherapeutic agents
Underlying medical problem (rare cases)
- Arteriovenus malformation
- Vascular tumor
- Benign intracranial hypertension
- Palatal or stapedial myoclonus
- Tustachian tube dysfunction
- Atemporal mandibular joint problem
- Acoustic neuroma (vestibular schwannoma)
- Meniere’s disease
Attentional and emotional contributors to tinnitus-related disturbance
Once a person begins to perceive the tinnitus signal as a consequence of hearing loss or other factors, the brain’s attentional filters may apply significance to the perceived sound. That, in turn, leads the system to pay particular attention to it on an ongoing basis.
This occurs within the subcortical regions of the brain, which are normally responsible for subconscious filtering of sounds.3 An example of this filtering is the ability of someone to be in a crowded room in a party and notice their own name being mentioned over the general din.
The emotional centers of the brain, which are predominantly in the subcortical regions of the brain, may become involved at this point. Involvement of the limbic system can lead to the attachment of a negative “emotional label” (such as fear) to the perceived sound. In addition, involvement of the autonomic system may trigger the body’s “fight or flight” response, which can be overwhelming and stressful to the person with tinnitus.
Cycle of disturbance
Since this stress can lead to further increases in the sensitivity of the auditory system – and hence amplification of the tinnitus signal – people can find themselves in a self-reinforcing cycle of increasing disturbance. This cycle can continue even after the original cause of the tinnitus (if temporary) has resolved. Indeed, tinnitus continues even after sectioning of the auditory nerve.4
In summary, although typically triggered in the first instance by a problem in the auditory system, tinnitus involves a cascade of higher neurological events that for many people lead to a significant level of disturbance. This may lead to stress, anxiety or even depression. Many people find difficulty with ability to sleep and concentrate. Some develop a sense of helplessness and loss of control over their lives as a result of their tinnitus.
1Reviewed by: Moller, A. (2007). The role of neural plasticity in tinnitus. Progr Brain Res, 166, 37-46; Kaltenbach, J.A. (2006). The dorsal cochlear nucleus as a participant in the auditory, attentional and emotional components in tinnitus. Hearing Research, 216-217:224-234. Georgiewa, P., Klapp, B.F., Fischer, F., et al. (2006). An integrative model of developing tinnitus based on recent neurobiological findings. Medical Hypotheses, 66, 592-600; Tyler, R.S. (2005). Neurophysiological models, physchological models, and treatments for tinnitus. In Tyler (Ed). Tinnitus Treatments: Clinical Protocols (pp. 1-22). Thieme, London; Jastreboff, P. (2004). The neurophysiological model of tinnitus. In Snow, J.B. (Ed). Tinnitus: theory and management (pp. 96-107). BC Decker, Hamilton.
2Vernon, J.A., Tabachnick Sanders,B. (2001). Tinnitus: Questions and Answers. Allyn and Bacon, Massachusetts, pgs 30, 64-65, 71-75, 80-81.
3 Hazell, J. W. P. (1995a). Models of tinnitus: Generation, perception: Clinical implications. In J. A. Vernon, & A. R., Moller (Eds.), Tinnitus mechanisms, (pp. 57-68). Needham, MA: Allyn & Bacon.
4 Mattox, et al (1999). Tinnitus as an unwanted outcome of medical and surgical treatments. In Hazell, J. (Ed) Proceedings of the Sixth International Tinnitus Seminar, Cambridge, pp 83-86.