Combining transcranial direct current stimulation and tailor-made notched music training to decrease tinnitus-related distress--a pilot study

Abstract

The central auditory system has a crucial role in tinnitus generation and maintenance. Curative treatments for tinnitus do not yet exist. However, recent attempts in the therapeutic application of both acoustic stimulation/training procedures and electric/magnetic brain stimulation techniques have yielded promising results. Here, for the first time we combined tailor-made notched music training (TMNMT) with transcranial direct current stimulation (tDCS) in an effort to modulate TMNMT efficacy in the treatment of 32 patients with tonal tinnitus and without severe hearing loss. TMNMT is characterized by regular listening to so-called notched music, which is generated by digitally removing the frequency band of one octave width centered at the individual tinnitus frequency. TMNMT was applied for 10 subsequent days (2.5 hours of daily treatment). During the initial 5 days of treatment and the initial 30 minutes of TMNMT sessions, tDCS (current strength: 2 mA; anodal (N = 10) vs. cathodal (N = 11) vs. sham (N = 11) groups) was applied simultaneously. The active electrode was placed on the head surface over left auditory cortex; the reference electrode was put over right supra-orbital cortex. To evaluate treatment outcome, tinnitus-related distress and perceived tinnitus loudness were assessed using standardized tinnitus questionnaires and a visual analogue scale. The results showed a significant treatment effect reflected in the Tinnitus Handicap Questionnaire that was largest after 5 days of treatment. This effect remained significant at the end of follow-up 31 days after treatment cessation. Crucially, tDCS did not significantly modulate treatment efficacy--it did not make a difference whether anodal, cathodal, or sham tDCS was applied. Possible explanations for the findings and functional modifications of the experimental design for future studies (e.g. the selection of control conditions) are discussed.

Conflict of interest statement

Competing Interests: Gottfried Schlaug owns shares in Tinnix, Inc. No relationship exists between Tinnix, Inc. and the results reported in this manuscript, and Tinnix, Inc. did not provide any support, material, or technology to this project. This does not alter the authors’ adherence to PLOS ONE policies on sharing data and materials.

Figures

Figure 1. Study design.

For each participant, the study took 45 days (4 days of pre-treatment waiting, 10 days of treatment, and 31 days of post-treatment observation). During the initial 5 days of treatment, transcranial direct current stimulation (tDCS) and the tailor-made notched music training (TMNMT) were applied simultaneously; during the remaining 5 days of treatment, only TMNMT was applied. Throughout the study, perceived tinnitus-related distress data were sampled repeatedly.

Figure 2. Average hearing thresholds.

Thresholds from 0.125 to 16(tDCS) condition (anodal group vs. cathodal group vs. sham group) and ear (left vs. right). The error bars denote standard error of the mean. Negative values reflect hearing loss.

Figure 3. Transcranial direct current stimulation (tDCS).

Time course of direct current strength in the different tDCS conditions.

Figure 4. Music spectra.

Schematic frequency spectra of original music (solid line) and flattened notched music (dashed dotted line).

Figure 5. Changes in Tinnitus Handicap Questionnaire (THQ) values during and after treatment.

Changes in THQ total scores relative to the baseline scores as functions of time (after tDCS1 + TMNMT2 vs. after TMNMT only vs. obs3 vs. obs31) and tDCS condition (anodal group vs. cathodal group vs. sham group). Bars represent means, error bars denote standard errors of the mean. Negative values reflect improvement. Dashed black lines indicate significant post-hoc tests. *p<.05, **p<.01; 1Transcranial direct current stimulation; 2Tailor-made notched music training.