Beeping, hissing or buzzing in the ear – tinnitus can seriously affect the quality of life of those affected. Researchers have now tested a new therapeutic approach in a large clinical study: their test subjects used a device every day for twelve weeks that electrically stimulated their tongue and played sounds through headphones. According to the study, symptoms improved significantly over the course of treatment and were much milder than before even a year later. However, there was no control group that received only a sham treatment for comparison. Further studies are therefore required to clarify the actual effectiveness of the therapy.
Tinnitus is a phantom noise that occurs in the person’s brain. Causes can include stress, tension or a blast trauma and other damage to the hair cells of the inner ear. To date, there have been few effective treatments. For example, health insurance companies pay for what is known as retraining, in which those affected learn to block out the noises in the ears under medical and psychological guidance. A new therapeutic approach is based on treating the cause in the brain: the nerve signals are to be modulated using electrical impulses in such a way that the noises in the ears are reduced in the long term.
Different stimulation patterns tested
Researchers led by Brendan Conlon from Neuromod Devices, a provider of medical devices, and Trinity College in Dublin have now tested this approach in a clinical study on 326 tinnitus patients. They use so-called bimodal neuromodulation, which combines electrical stimulation and acoustic signals. According to previous studies, electrical stimulation of the scalp, neck or tongue increases the plasticity in large parts of the brain. The acoustic signals in turn specifically activate the brain regions that are responsible for hearing. Bimodal neuromodulation has already shown promising results in animal studies, and a pilot study on human subjects has also shown positive results.
As the team around Conlon explains in the current publication, there are numerous variables that can influence the effectiveness: Where exactly, with what intensity and at what intervals are the electrical impulses set? Are they synchronous with the acoustic signals or are they delayed? And which audio frequencies are used? To test all possible combinations, thousands of subjects would be required. For reasons of feasibility, the scientists decided to divide their subjects into just three groups in which various factors of the therapy were varied. In this way, they were able to test several therapy schemes in parallel. The disadvantage of this approach, however, is that you cannot attribute possible effects to a single factor. Since they also did without a control group, it is unclear how great the effect is compared to a sham treatment.
Fast and long-term recovery
All three groups were instructed to use a device from Neuromod Devices for one hour a day for twelve weeks, which emits a certain pattern of electrical impulses to the tongue and at the same time plays sounds through headphones. In group 1 the impulses and noises were simultaneous and the tones played covered a wide frequency spectrum from very low to very high. In group 2 the frequency spectrum was the same, but the tones and electrical impulses were slightly offset in time. Group 3 only heard low tones, which also had a significantly longer delay compared to the electrical impulses.
After six weeks, subjects in all three groups showed a clear improvement in symptoms. This trend continued over the next six weeks of treatment, but was less pronounced than at the start of treatment. The researchers suspect that the reason is that the brain initially reacts very strongly to the new stimuli, but gets used to them over time and shows less clear reactions. For future studies, they therefore suggest changing the therapy regimen halfway through the trial period in order to reduce habituation effects.
Further studies planned
One year after completing treatment, subjects in Groups 1 and 2 still had significantly milder tinnitus symptoms than before. The researchers conclude that it does not matter whether the electrical and acoustic signals are simultaneous or slightly delayed in terms of effectiveness. In group 3, on the other hand, the positive effect of the treatment was only weakly pronounced one year later. The researchers can only guess whether the reason for this was that only low notes were played or whether the time lag between the electrical and acoustic signals was too great.
Side effects appeared only sporadically and included, for example, headaches and abnormal sensations on the tongue. In a survey, most of the test subjects stated that they were satisfied with the treatment and would recommend it to others. The current study has shown that bimodal neuromodulation is a therapy with few side effects that is well accepted by patients. Compared with other studies, for example on cognitive behavioral therapy for tinnitus, the test subjects reported a particularly significant relief of their symptoms. Future studies will have to show whether the therapy is actually more effective than previous alternatives. Conlon’s team is now planning further investigations in which they want to explore different therapy schemes in more detail.
Source: Brendan Conlon (Neuromod Devices Limited, Dublin) et al., Science Translational Medicine, doi: 10.1126 / scitranslmed.abb2830