tDCS and tinnitus A meta analytic exploration into efficacy and optimization

Millions of Americans suffer from tinnitus, or ringing of the ears. Despite its prevalence, treatment for tinnitus is limited, with most approaches focusing on making the symptoms tolerable, instead of treating the underlying neurological causes. Recently however, brain stimulation techniques, such as transcranial direct current stimulation (tDCS), have emerged offering a new method to interact with the brain and offering hope as a new approach to treating the underlying causes of tinnitus, not just making the symptoms tolerable. In the present meta-analysis, we analyzed the results from 17 controlled trials and 5 uncontrolled case studies to determine the efficacy of tDCS for treating tinnitus. Additionally, we performed sub-analyses to test how different tDCS parameters may alter the efficacy of treatment. Overall, we found a small but significant effect (Overall Hedges g of 0.17 (95% CI 0.09-0.25)) of tDCS on tinnitus symptoms. However, mechanistically we found that targeting the DLPFC improved symptoms significantly more than other targets, including targeting the auditory cortex directly. This along with the subjective outcome measures currently available, suggest that while tDCS does offer a benefit to treating the symptoms, it does not appear to treat any underlying causes. It is the opinion of the authors therefore that tDCS should be used in addition to traditional interventions to make the symptoms more tolerable. As covered in the discussion, future research should explore more objective measures of tinnitus in order to better assess the efficacy of tDCS and other brain stimulation methods, with the hope of developing a causal treatment of tinnitus.