Neurological Basis of Disturbing 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 assocated with tinnitus and its impact on their quality of life is primarily the result of his or her 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
Usually, tinnitus is triggered in the first instance 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 types of drugs and medication, middle ear infections, or any one of many other causes.
Regardless of the cause of the hearing loss, and whether it is permanent or temporary, it can lead to the changes in the activity of neurons in the auditory system, which is then interpreted by the auditory cortex as sound.
Other Tinnitus Triggers
In a small proportion of cases, tinnitus arises from a condition that requires medical or surgical intervention.
Drugs that have been implicated in hearing damage and tinnitus include2:
- anti-inflammatories
- antibiotics (aminoglycosides)
- antidepressants (heterocyclines)
- aspirin
- quinine
- loop diuretics
- chemotherapeutic agents (cisplatin)
In rare cases, tinnitus might result from an underlying medical problem, such as:
- arteriovenus malformation
- vascular tumor
- benign intracranial hypertension
- palatal or stapedial myoclonus
- eustachian tube dysfunction
- temporal mandibular joint problem
- acoustic neuroma (vestibular schwannoma)
- otosclerosis
- Meniere’s disease
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 might also be required.
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 then apply significance to the perceived sound, leading 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 a negative “emotional label” (such as fear) being attached 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.
Since this stress caused by tinnitus 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 been 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 their ability to sleep and to concentrate are interfered with, and they may 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.