Look at this picture. What do you see? Maybe you’ll see it straight away, or maybe it will take some time. But, if you look for long enough you will eventually see a Dalmatian dog sniffing at the ground.
Although it is not obvious why, if we truly understand the process of seeing the dog in the dots then we will understand most of what is known about how tinnitus occurs.
The dots represent spontaneous firing of brain cells in the hearing pathway of the brain. Brain cells like to maintain a particular average firing rate, and when hearing damage takes away some of their usual input, they become overactive in order to maintain it. This is akin to making the dots stronger or more vivid. Also, imagine the dots keep flickering on and off; it makes a difference whether they all flash at the same time, or are staggered. This is akin to ‘neural synchrony’, which is a measure of the extent to which multiple brain cells fire at the same time.
But not everybody with hearing loss will develop tinnitus, and some people with tinnitus have no detectable hearing loss. Hearing loss affects the firing rate and synchrony of hearing brain cells but, ultimately, what determines whether tinnitus occurs is whether the brain (subconsciously) finds what it considers to be a meaningful pattern in this spontaneous firing. Many factors may influence this, including genetics, stress levels, brain chemistry, attention, and even just chance. Recent work has found that people with tinnitus find patterns in complex, changing sequences of sounds differently (probably better) than people of the same age, sex and hearing profile but without tinnitus.
Once you have seen the dog, you cannot un-see it. Years can go by, and whenever you see the picture again, you will rapidly see the dog again.
Present treatments cannot take the dog away, but psychologically-based therapies can help change our reaction to it, for instance reclassifying it from a pit bull to a spaniel.
What does this analogy tell us about tinnitus treatments? Research treatments currently being trialled include measures to break up the synchrony of brain cell firing. In future if we can repair damage to the inner ear, the strength of spontaneous firing might diminish. Finally, if we can identify the process by which the brain ‘learns’ the pattern within the brain cell firing (a work currently in progress), maybe we can eventually find a way to help it ‘un-learn’ it.
Tinnitus research is expanding all the time as we explore these avenues and more, but for now we still do not know which will provide the eventual cure, and when.
[Photo credit: Action on Hearing Loss]
