High-Definition Transcranial Direct Current Stimulation for Tinnitus Relief: Optimisation of the 4 x 1-Ring Radius

Abstract

Background: Tinnitus is the phenomenon whereby an auditory sensation is perceived in the absence of an external sound stimulus. Recently, a novel non-invasive brain stimulation technique called high-definition transcranial direct current stimulation (HD-tDCS) was investigated for tinnitus modulation with promising results (1). To date, only optimisation of HD-tDCS intensity and duration stimulation parameters has been investigated in the context of tinnitus modulation. Aims: To optimise the 4 x 1-ring radius of HD-tDCS over the left temporoparietal area (LTA) for tinnitus modulation. It is predicted that HD-tDCS with a large radius (7 cm) will modulate measures of tinnitus loudness and annoyance more than HD-tDCS with a small radius (3.5 cm), and that HD-tDCS of the LTA will modulate measures of tinnitus loudness more than tinnitus annoyance. Methods: A double-blind, sham-controlled, within-subjects design was used. Fourteen participants underwent 20-minute sessions of active HD-tDCS with 3.5 cm radius, 7 cm radius, and sham HD-tDCS. The order of the sessions was randomised and there was a washout period of at least 3 days between sessions. Subjective ratings of tinnitus loudness and annoyance were assessed using tinnitus loudness and annoyance rating scales at 6 time points during stimulation. Results: Repeated measures ANOVA (RM-ANOVA) revealed a significant main effect of time on loudness (P = 0.014) but not annoyance ratings (P = 0.128). However, there was no significant main effect of condition or interaction effect between condition and time on either loudness (P = 0.451 and 0.616, respectively) or annoyance ratings (P = 0.671 and 0.671, respectively). When each condition was considered separately, one-way RM-ANOVA revealed a significant effect of the 3.5 cm radius condition on loudness ratings (P = 0.007), but not annoyance ratings (P = 0.193), and a significant effect of the 7 cm radius condition on annoyance ratings (P = 0.044), but not loudness ratings (P = 0.48). Conclusion: The findings of this study show promise for the use of HD-tDCS for tinnitus suppression. However, the effect sizes were small, suggesting that further optimisation of stimulation parameters is needed before HD-tDCS can be considered a clinically useful tool for tinnitus intervention.