Abstract
BackgroundTinnitus is the perception of sound in the absence of any external acoustic stimulation. Transcranial direct current stimulation (tDCS) has shown promising though heterogeneous therapeutic outcomes for tinnitus. The present study aims to review the recent advances in applications of tDCS for tinnitus treatment. In addition, the clinical efficacy and main mechanisms of action of tDCS on suppressing tinnitus are discussed.MethodsThe study was performed in accordance with the PRISMA guidelines. The databases of the PubMed (1980–2018), Embase (1980–2018), PsycINFO (1850–2018), CINAHL, Web of Science, BIOSIS Previews (1990–2018), Cambridge Scientific s (1990–2018), and google scholar (1980–2018) using the set search terms. The date of the most recent search was 20 May, 2018. The randomized controlled trials that have assessed at least one therapeutic outcome measured before and after tDCS intervention were included in the final analysis.ResultsDifferent tDCS protocols were used for tinnitus ranging single to repeated sessions (up to 10) consisting of daily single session of 15 to 20-min and current intensities ranging 1–2 mA. Dorsolateral prefrontal cortex (DLPFC) and auditory cortex are the main targets of stimulation. Both single and repeated sessions showed moderate to significant treatment effects on tinnitus symptoms. In addition to improvements in tinnitus symptoms, the tDCS interventions particularly bifrontal DLPFC showed beneficial outcomes on depression and anxiety comorbid with tinnitus. Heterogeneities in the type of tinnitus, tDCS devices, protocols, and site of stimulation made the systematic reviews of the literature difficult. However, the current evidence shows that tDCS can be developed as an adjunct or complementary treatment for intractable tinnitus. TDCS may be a safe and cost-effective treatment for tinnitus in the short-term application.ConclusionsThe current literature shows moderate to significant therapeutic efficacy of tDCS on tinnitus symptoms. Further randomized placebo-controlled double-blind trials with large sample sizes are needed to reach a definitive conclusion on the efficacy of tDCS for tinnitus. Future studies should further focus on developing efficient disease- and patient-specific protocols.
Highlights
Tinnitus is the perception of sound in the absence of any external acoustic stimulation
Total of 33 records were excluded from the further assessment and 53 records were entered into the screening phase in which 8 conference abstracts, 1 book, 2 case reports and 4 editorials were excluded from the review
The review focuses on the advances in applications of Transcranial direct current stimulation (tDCS) for treatment of tinnitus and the important factors in the resulting outcomes
Summary
Tinnitus is the perception of sound in the absence of any external acoustic stimulation. Tinnitus perception is an integrated output of a large and complicated brain network comprising of different subnetworks with overlapping functions [2, 11]. In this impaired network, each subnetwork represents a clinical aspect of tinnitus such as distress, loudness, and laterality [11,12,13]. Neurobiological and neuroimaging findings have shown that abnormal activities of the non-auditory regions associated with cognitive and attentional functions as well as limbic processes probably contribute to the unpleasant and distressing aspects of tinnitus [11, 14]. Considering the engagements of AC and DLPFC in the tinnitus perception, these regions may be good targets for any therapeutic intervention for tinnitus
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