Optimization of Transcranial Direct Current Stimulation for Tinnitus Management

Neuromodulation is defined as the process of augmenting the plasticity of the brain by using invasive or non-invasive methods. Neuromodulation has been used for transient tinnitus suppression for a decade. The aim of the present study was to optimize the parameters of transcranial direct current stimulation (tDCS) of dorsolateral prefrontal cortex (DLPFC) for tinnitus suppression. This study was the first attempt at investigating the number of sessions needed for optimum tinnitus suppression. One hundred one participants (average age 59.87 years) with average tinnitus duration of 5.9 years underwent tDCS of DLPFC. The following factors were optimized in the dose-response design: current intensity (1.5 mA or 2 mA), stimulation duration (20 min or 30 min) and number of stimulation session (2 or 4 or 6 or 8 or 10) with 3 to 4 days washout period between each session. Participant underwent minimum of 2 sessions in 1 week or maximum of 10 sessions in 5 weeks' time. Tinnitus loudness was measured in pre-post design using 10 point tinnitus loudness numeric rating scale. There was a significant reduction in the tinnitus loudness after the tDCS of DLPFC compared to before the treatment. There was no significant difference between the intensity (1.5 mA or 2 mA) and duration (20 min and 30 min) of stimulation. As the number of session increased there was a higher reduction in the tinnitus loudness, however it reached a plateau after 6 sessions. There was a nonlinear cumulative change in the cerebral function as a result of multi session tDCS. Present study revealed a non-linear cumulative change in the cerebral function as a result of multi session tDCS. Researchers have made few attempts to investigate the impact of multi session tDCS on tinnitus suppression; however these attempts did not result in tinnitus relief. The likelv reason for this could be due to the difference in research design and lack of optimization. The optimum setting for repeated tDCS stimulation of DLPFC to reduced tinnitus loudness would be: intensity - 1.5 mA, duration - 20 minutes, sessions - 6 sessions over 3 weeks' time with a washout period of 3 to 4 days.