The stress response in humans is designed to keep us alive in threatening situations. It is remarkably well adapted to this task triggering as it does a whole brain and body response to maximise the chance of survival. From rapid release of adrenaline, dilation of the pupils to reduced blood flow to the digestive system some profound changes take place over a very short period of time. This can include a phenomenon known as ‘Auditory Exclusion’ whereby hearing is temporarily reduced in order that the brain can focus more on visual inputs. When the hearing returns we are likely to be listening frantically for any sounds we may have missed.
There is obviously a range of intensity of the stress response from mildly annoyed to full on fight or flight as briefly described above. At lower levels of stress there can be a degree of ‘hyper-vigilance’ where we feel under some degree of threat but its source isn’t obvious. In this state the normal process of ‘sensory gating’ where we are selective about what stimuli we pay attention to, i.e. listening to a friends voice in a noisy café, can be weakened. It is likely that we can then become very aware of the normal background activity in the nerve of hearing known as stochastic firing.
When we hear externally generated sounds we are not experiencing the sound as it presents in the air. The physical vibration of air molecules is transduced (converted) by the inner ear or Cochlea into a pattern of electrical signals. This pattern of signals is broken down into their constituent pitches or frequencies which are responded to by dedicated nerves all the way up the auditory pathway, this is known as the tonotopic ‘map’ of sounds. Every sound we hear has a unique blend of frequencies, volumes, gaps and duration. From even before birth our brain is making a comprehensive catalogue of each ‘sound pattern’ and what it represents. In this way we learn the meanings of different words in speech and to tell for example a car horn from the squeal of a bus stopping nearby.
Tinnitus is sometimes called a ‘Threshold Perception’ in that to a large extent it is either filtered INTO the conscious mind or OUT entirely. For most of our lives the signal that can be heard as tinnitus is normalised and filtered out by the brain. Once the random noise in the nerve of hearing crosses that threshold into consciousness we rapidly have to try and classify it. And here it is that things can go rapidly wrong for us. We are hard-wired to treat new stimuli as a threat first and only later to work out if that assessment was correct. In the case of our ancestors wondering if that was a breeze or a tiger moving the grass that was a highly useful heuristic.
With tinnitus we match its ‘sound pattern’ to the closest match in our catalogue. Very often this is heard as a high pitched whine or screech. This is likely to be because even where our hearing is normal for most speech sounds, think 100 – 8,000Hz most people over the age of 30 will have a greater or lesser degree of ‘cryptic’ or hidden hearing loss in the higher tones from 8,000 – 20,000Hz. So although the stochastic or random firing of the nerve of hearing may well be equally loud at all frequencies it sounds high-pitched to the person with tinnitus because the lower frequencies are being covered up or ‘masked’ by environmental sounds all around us. Nerve studies have shown that tinnitus activity is only around 9dB whereas the typical room noise is around 35dBA.
So in summary stress can cause changes in how we process the signals we hear both externally and internally. These changes can cause normal nerve activity to be abnormally heard. Once heard a cascade of mal-adaptations can take place that lead us to actively filter tinnitus into our consciousness and experience distress.
Our Tinnitus UK experts understand this process very well and are able to use our unique Cognitive Tinnitus Therapy programme and specialist extended high frequency tinnitus hearing aids to help you to tackle the distress and distraction caused by tinnitus as effectively as possible. Book now for a full tinnitus assessment.
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