MECHANISMS OF TINNITUS

How does tinnitus ‘work’?

I mentioned ‘sensations’ in my description of tinnitus.  Patients ask me to explain this so that they can understand the mechanism of tinnitus.  So let us use a model to explain it: structure, function and mind; or, anatomy, physiology, cognition and emotion. 

Tinnitus arises when the inner ear receptors, the hair cells, become destabilized as a result of mechanical damage, metabolic change, or body-system effects, inflammation for example.  This leads to a loss of synchronous nerve firing in the fibres that run from the receptors along the auditory nerve to the auditory centre in the brain.  So the pattern that the brain receives is no longer an organized message with some meaning.  Instead it receives a ‘foreign’ code.  Since the brain is wired to recognize patterns and attribute meaning to them, the fact of a bizarre code coming in produces what I call cognitive dissonance.  The signal is perceived but it is jarring and it doesn’t make sense. In fact it is really disturbing.  Our brain ‘knows’ that information arises from an outside source yet this signal comes from inside, rather like a phantom that is there but not seen.  This is distressing and it produces a reaction in the arousal system of the brain so we are on the alert for danger, rather as our ancestors were when life was about survival in harsh conditions.  Almost at the same time as we become aroused by the tinnitus we also experience body sensations associated with the dissonance of it: fear and anxiety mainly so that we want to avoid this thing, this tinnitus, if we can.  Due to the amazing networks in our brain the complex that is the incoming dys-synchronous signal, arousal and fear, lead to the involvement of another brain area, our prefrontal cortex, that ‘thinks’ about this whole event, worries about it, runs it around and around in our mind’s ‘default’ cognitive mode, evaluates it, judges it constantly.

This will give you an idea of the complexity of the networks that get set up in this process.  What I have described is not a straightforward linear process but is a series of circuits or networks that hook up and become wired together with the passage of time.  Then there are various factors that contribute to the network; external factors you might say, such as stress, lack of sleep, or hearing loss and these play into the networks and make them work harder and faster on some days than others: rather like a horse galloping fast when the rider is distracted and struggles to hold the reins.

Key points:

  • Tinnitus originates with disturbance in the peripheral auditory system, the outer hair cells of the inner ear.
  • Tinnitus also involves central networks in the brain; these are linked to the arousal and emotional centres.
  • Factors such as the actual hearing loss, our cognitive capacity, play a mediating role in the experience of tinnitus.