P Lucas, of Palmerston North, asks :-
What causes tinnitus?
Grant Searchfield, an audiologist at the University of Auckland, responded.
One answer would be we don’t know, but that isn’t entirely true. In ancient times it was believed that tinnitus “ringing-in-the ears” was caused by Gods whispering in the ear, in modern times it was thought that maybe the ear was making the sound and sending increased activity to the brain to hear it.
What we now know is that it is a very complicated process. Tinnitus often starts by changes at the ear, but usually a reduction in ear activity – this can happen with hearing loss – then the brain tries to compensate “make-up” for the reduced activity and makes its own noise.
Normal sound causes vibrations on fluid in the inner ear (called cochlea) which contains tiny hair cells (called this because they look like they have hair, not because they hear!) that move to this vibration resulting in electrical activity in the hearing nerve. With ear damage these hair cells don't work as well and activity in the hearing nerve drops.
Loud sounds can cause tinnitus, because these loud sounds temporarily upset the balance of activity coming from the ear - the brain reacts to this change, but creates a false "image" of sound.
When that happens, parts of the brain involved in hearing, and other parts associated with attention, memory and emotion become activated (this is why some people are annoyed by tinnitus sounds and others aren’t). We also know that other senses can make tinnitus louder or quieter – some people can turn tinnitus on/off by staring at things others move their head or jaw in a certain way and it changes their tinnitus.
So tinnitus is very complicated, it is still not possible for us to “see” tinnitus in brain scans or measures of brain activity, but scientists are getting closer.