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.
Highlights
Chronic tinnitus (i.e. permanent and lasting ringing sensation in the ear(s) in the absence of a physical sound source) is a significant public health concern that impairs the quality of life for millions of patients around the world
We investigated whether transcranial direct current stimulation (tDCS) polarity over left auditory cortex would modulate the efficacy of short-term combined tDCS + tailormade notched music training (TMNMT) treatment for not severely hearing impaired patients suffering from chronic tonal tinnitus
This study investigated whether tDCS polarity over left auditory cortex would modulate the efficacy of a combined tDCS + TMNMT short-term treatment for not severely hearing impaired patients suffering from chronic tonal tinnitus
Summary
Chronic tinnitus (i.e. permanent and lasting ringing sensation in the ear(s) in the absence of a physical sound source) is a significant public health concern that impairs the quality of life for millions of patients around the world. In the majority of cases, tinnitus is probably triggered by inner ear hair cell injury. The neural generators of tinnitus are most likely located in the central auditory pathway. One possible consequence of injury to hair cells (and the subsequently decreased input to tonotopic maps in auditory cortex) is a loss of lateral inhibition from cortical neural populations which would normally code activity from the damaged and silent receptors. In many if not all cases of chronic tinnitus, nonauditory brain structures are part of the tinnitus generating and tinnitus sustaining networks [5]
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