Tinnitus can be caused by the following:
exposure to loud noise
a side effect of medication
ear or head injuries
diseases of the ear
Tinnitus often occurs in conjunction with an auditory impairment, for instance after an acute loss of hearing.
For individuals with long-term tinnitus, one or more of the causes above have, at some point, led to an auditory malfunction. The brain’s attempt to compensate for this malfunction is the start of a vicious cycle.
The auditory cortex is the part of the brain that is responsible for hearing. Every stimulus perceived by the ear is transmitted to and processed by the auditory cortex. The nerve cell assemblies in a specific area of the auditory cortex are 'tuned' to a certain frequency, similar to the arrangement of keys on a piano.
No matter what triggers may be responsible for the tinnitus – noise, medication, stress – they all lead to an interruption of the signal transmission from the ear to the auditory cortex. This means that some of your nerve cell assemblies no longer receive any signals. To stay with the piano image: some of the piano's keys no longer work and cannot be struck by the pianist.
However, these nerve cell assemblies do not react to the lack of stimulus by simply remaining 'silent'. Instead the nerve cells begin to 'chatter' spontaneously and become synchronously attuned to one another.
Once they have become hyperactive and synchronous in this way, the nerve cells simulate a tone that the brain 'hears' – the tinnitus tone. Coming back to the piano; the broken keys have created their own permanent tone even without the keys being struck by the pianist.
Over time, this pattern strengthens and the tinnitus becomes permanently anchored – the brain has learnt a phantom sound.