A Critical Review of the Evidence for Notched Sound Therapy as a Treatment for Tinnitus: A Summary
Editor’s Note: From time to time The Hearing Blog presents guest articles for our Readers to consider. Today’s article written by Peter Phua, a graduate of McMaster University’s medical program, is a critical review of the summary of evidence for Notched Sound Therapy as a treatment for tinnitus. Phua is also the developer of AudioNotch, an on-line provider of custom Notched Sound Therapy for tinnitus patients.
Previously, I’ve written a Guest Article on The Hearing Blog on the subject of Notched Sound Therapy as a treatment for tinnitus. Today, I’m interested in taking a look at some of the criticism of the existing literature around Notched Sound Therapy, in order for the reader to gain a better assessment of where the research is at.
Mark Bennett, a master’s student at the University of Western Ontario has written an excellent thesis on this very subject.1 Although the paper was unpublished, Bennett provided some great analysis on the subject. The abstract is as follows:
This critical review examines the effects of notched-sound therapy on the human auditory system and its’ potential as a novel and effective treatment option for tinnitus. Studies evaluated consisted of one mixed groups randomized clinical trial, two mixed groups pseudorandomized clinical trials, and two mixed groups non-randomized clinical trials. Analyses of these studies revealed moderate evidence for notched-sound’s ability to induce changes in the auditory cortices and reduce tinnitus-related symptoms. Future research directions and clinical applications will be discussed.1
What follows will be a summary for hearing health professionals.
Bennett begins his paper by reviewing the proposed mechanism behind Notched Sound Therapy. Although neuroplastic changes in response to peripheral deafferentiation (loss of peripheral inputs from sensory cell death) are presumably the cause of tinnitus, the same neuroplastic mechanisms could, in theory, be recruited to reverse the changes that cause the tinnitus percept,1
By targeting auditory cortex neurons that code for tinnitus frequencies, through customized notched sounds, maladaptive neural structuring that is causing tinnitus perception may be remedied.1
Specifically, such changes include:
The unmasking of existing cortical connections, lack of local inhibitory connections, alterations in cell membrane excitability and synaptic efficacy.1
Analysis of Notched White Noise Experiment (randomized controlled trial):
An Italian randomized clinical trial with a sample size of 43 recruited patients who listened for 1.5-3 hours/day over a 1 year span. Notched White Noise with a notch width of one equivalent rectangular bandwith was used.2 The results were significant:
The final absolute tinnitus loudness decreased significantly by roughly 12dB from baseline in the WWN group upon completion of the treatment the perception of tinnitus was entirely eliminated in four of the twenty participants in the WWN group. None of the participants in either control group completely recovered.1
Bennett concludes the following:
The results of this study provide moderate support for a notched sound exposure as a potential treatment option for tinnitus sufferers and warrants future search in this area.1
He (Bennett) did, however, have some reservations about the lack of neurophysiological data to correlate to the reported subjective decreases in tinnitus volume, and pointed out a major limitation of the study – “it failed to follow the participants longitudinally posttreatment.”1 Thus, the question of whether or not the effects of Notched Sound Therapy persist in a permanent fashion is still an open one.1
Analysis of Notched Music Experiment (pseudo-randomized clinical trial):
A German study with a sample size of 23 was recruited with the following parameters:3
1. Chronic tinnitus;
2. Unilateral/strongly lateralized tinnitus;
3. Tonal tinnitus;
4. Tinnitus frequency < 8kHz;
5. No severe hearing impairment;
6. No neurological or psychiatric complications.1
They listened daily for two hours per day for one year.3 Unlike the previous study, this one involved neurophysiological correlates:
The treatment group showed significant reductions in both tinnitus loudness and auditory cortex evoked activity relative to baseline.1
However, the failure to fully randomize patients leaves open the possibility of multiple confounding variables corrupting the study result.1 While promising, the value of the control group, without randomization (and with such a small sample size), is basically null.1 This was a significant methodological flaw.
Analysis of Effective Frequency Range of Notched Music Experiment (non-randomized clinical trial):
Another German study by the same group was performed, this time, with a more short term and intense treatment window.4 Experimental groups were grouped into those with tinnitus frequencies < 8 kHz and those with tinnitus frequencies >8 kHz, in order to determine if the frequency had a role in the treatment effect.4 It also provided positive results (but similarly, was not an R.C.T.):4
For the low frequency group, significant reductions were found in at least one outcome measure at all intervals post-treatment. At 31 days post-treatment there was a significant reduction in tinnitus-related distress (t = 2.38, p < 0.01), but not in any other outcome measure. For the high frequency group, there was not a significant change in tinnitus related distress or tinnitus loudness at any of the four points measured compared to baseline. A possible reason for the null results in this group, suggested by the authors, is that the music contained little high frequency energy. Future research with this population should include high frequency enriched stimuli.1
A short term course of therapy lasting only days resulted in a decay of the therapeutic lowering of tinnitus volume over subsequent days calling into the question the permanence of the therapy’s effects: 4
Whether such permanent neural changes can occur through notched sound exposure can occur in the human auditory system remains unanswered.1
Bennett also had similar reservations about the methodology of this study:
The study has several limitations such as failure to utilize a randomized, double-blind procedure with a control group and small sample size.1
Conclusions and Clinical Implications:
Bennett reviews the hypothesized mechanisms for action for Notched Sound Therapy – the strengthening of existing lateral inhibitory networks:
[Researchers] attribute their positive to results to the ability of notched sound to reduce the excitability of hyperactive auditory neurons. This reduction would be caused by strengthening weakened inhibitory networks in the critical tinnitus frequency band.1
Bennett had many reservations about the lack of neurophysiological correlates to the tinnitus percept, and was skeptical even when some were provided (such as MEG measurements in some of the Notched Music studies):
MEG measurements represent large areas of the nervous system and should be interpreted with caution. The MEG results across studies were inconsistent.1
Overall, however, it is the methodological limitations of the studies that prevents a stronger endorsement of Notched Sound Therapy at this time:
The lack of longitudinal randomized controlled studies, disclosure of statistical methods, and omission of many important statistical data renders the results of these studies questionable.1
The studies under review differed in many ways including: forms of notched sound (noise vs. music), tinnitus loudness and frequency matching, length of exposure, outcome measures, and participant inclusion (hearing thresholds, tinnitus characteristics, and age).1
In summary, given the positive evidence at hand, while promising, more research needs to be done on Notched Sound Therapy to determine its efficacy and recommend it as a standard clinical treatment for tinnitus:
There is not yet enough evidence to support that such a form of treatment is ready for clinical implication.1
Overall, I felt that Bennett’s paper represented a fair appraisal of the limitations of the evidence for Notched Sound Therapy. At this time, the scientific evidence is provisional, and strong claims about its efficacy cannot be made. Larger scale randomized controlled are indicated for further investigation of Notched Sound Therapy’s efficacy, along with the incorporation of neurophysiological correlates to the tinnitus percept.
- Bennett, Mark (2012). Critical Review: Efficacy of notched-sound therapy for neural plasticity mediated tinnitus treatment.
- Lugli, M., Romani, R., Ponzi, S., Bacciu, S., Parmigiani, S. (2009). The windowed sound therapy: A new empirical approach for an effective personalizes treatment of tinnitus. International Tinnitus Journal, 15, 51-61.
- Okamoto, H., Stracke, H., Stoll, W., Pantev, C. (2010). Listening to tailor-made notched music reduces tinnitus loudness and tinnitus-related auditory cortex activity. PNAS, 107, 1207-1210.
- Teismann, H., Okamoto, H., Pantev, C. (2011). Short and intense tailor-made notched music training against tinnitus: The tinnitus frequency matters. Plos ONE, 6, 1-8.
- AudioNotch FAQ section 11: Are the effects permanent?
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