Many of us have just spent the Christmas season with a persistent and irritating ringing noise in our ears. But now that the relatives have gone home for the year, it’s worth remembering that a large proportion of the population suffers from a more persistent ringing sensation – tinnitus. It happens in the absence of noise, it’s one of the most common symptoms of hearing disorders, and it’s loud enough to affect the quality of life of around 1-3% of the population.
There have been many suggested treatments but none of them have become firmly established and most simply try to help people manage or cope with their symptom. Now, Hidehiko Okamoto from Westfalian Wilhelms University has developed a simple, cheap and enjoyable way of reducing the severity of the ringing sound. The treatment has showed some promise in early trials and even better, it is personally tailored to individual patients.
The method is simple. Find out the main frequency of the ringing sound that the patient hears – this becomes the target. Ask the patient to select their favourite piece of music and digitally cut out the frequencies one octave on either side of this target. Get the patient to listen to this “notched” piece of music every day. Lather, rinse and repeat for a year.
Okamoto tried this technique in a small double-blind trial of 23 people, eight of whom were randomly selected to receive the right treatment. Another eight listened to a piece of music that had a random set of frequencies cut out of it, while seven were just monitored. The treatment seemed to work. After a year, the treatment group felt that their ringing sensation was around 30% quieter, while the other two groups showed no improvements.
This is obviously a very preliminary study with only a small number of people. Nonetheless, it’s encouraging because finding workable treatments for tinnitus has been difficult because until recently, we didn’t really understand what causes it. The key point is that it’s not a problem with the ears, but with the brain – specifically, the auditory cortex which processes the sounds we hear.
The neurons of the auditory cortex are arranged in a sort of frequency map, with cells that respond to low frequencies at one end and those that respond to high frequencies at the other. Distortions or damage to parts of this map result in tinnitus. This could be due to an injury directed at specific groups of neurons. It could even be due to the gradual hearing loss that accompanies old age.
As the connections between the auditory cortex and other parts of the brain start to wane, some neurons within the cortex stop working properly. But rather than slide into inactivity, they become rewired so that they respond to the same frequencies as their neighbours. Certain parts of the frequency map essentially fuse with one another. Indeed, scientists have found that the activity of the auditory cortex neurons corresponding to the tinnitus frequency is greater than normal, and the more active they are, the more intrusive the ringing is. It’s a case of the brain’s own flexibility becoming its undoing.
Okamoto’s treatment was inspired by earlier work, which showed that you could reduce the activity of neurons in the auditory map by playing people music with the frequency in question removed. It’s possible that listening to this music silences the overactive neurons corresponding to the notched frequency. Alternatively, these neurons could be actively suppressed by their buzzing neighbours.
Either way, Okamoto found that the notched music reduced the activity of the affected neurons within the auditory cortex of his patients. These physical measurements matched the patients’ descriptions of their own experiences, and the two measures were strongly related.
Okamaoto thinks that getting patients to pick their own favourite music was an important part of the technique. The music we like can grab our attention and triggers the release of dopamine, a chemical involved in feelings of reward and pleasure. It’s also important for rewiring parts of the cortex, when our brain needs to be flexible.
Reference: Okamoto et al. 2009. Listening to tailor-made notched music reduces tinnitus loudness and tinnitus-related auditory cortex activity. PNAS doi: 10.1073/pnas.0911268107