Abstract
Neuromodulation is defined as the process of augmenting neuroplasticity via invasive or non-invasive methods. Tinnitus is the perception of sound in the absence of its external source. The objective of this study was to optimize the parameters of transcranial direct current stimulation (tDCS) of dorsolateral prefrontal cortex (DLPFC) for tinnitus suppression. The following factors were optimized in the dose-response design (n = 111): current intensity (1.5 mA or 2 mA), stimulation duration (20 min or 30 min), and number of stimulation sessions (2, 4, 6, 8, or 10), with a 3–4 day washout period between each session. Participants underwent a 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 a 10-point numeric rating scale. There was a significant reduction in tinnitus loudness after tDCS of DLPFC. There was no significant difference between the intensity and duration of stimulation. As the number of sessions increased, there was a higher reduction in the tinnitus loudness; however, this effect plateaued after 6 sessions.
Highlights
Initial studies have demonstrated the duration and strength of the transcranial direct current stimulation (tDCS) after-effects are dependent upon the intensity and duration of stimulation[13]
There are several open questions: how many sessions of tDCS are needed for optimal results? What should the washout period be between the tDCS sessions? What would be the outcome of head-to-head comparisons of multiple sessions of tDCS? The current trial was designed with the aim to optimize tDCS of dorsolateral prefrontal cortex (DLPFC) by investigating the impact of current intensity (1.5 mA or 2 mA), duration (20 minutes or 30 minutes), and number of sessions (2, 4, 6, 8, or 10) on tinnitus suppression
A repeated-measures ANOVA yielded a significant effect for pre- vs. post-stimulation tinnitus loudness numeric rating scale (F(1,93) = 95.29, p < 0.001) showing a significant reduction in tinnitus loudness after tDCS treatment (M = 6.48, Sd = 1.98) in comparison to before treatment (M = 4.91, Sd = 2.17)
Summary
Initial studies have demonstrated the duration and strength of the tDCS after-effects are dependent upon the intensity and duration of stimulation[13]. Most studies do not account for the number of sessions needed to induce a therapeutic effect in patients Each of these parameters is potentially relevant for clinical outcomes. There has been some early research in the area of optimizing tDCS stimulation parameters (intensity, duration, and location) for tinnitus suppression[25,26,27]. Shekhawat et al.[26], for example, conducted a dose-response study and found that tDCS of left temporoparietal area (LTA) with a 2-mA current intensity and a 20-minute duration is the most effective setting for transient tinnitus suppression. The current trial was designed with the aim to optimize tDCS of DLPFC by investigating the impact of current intensity (1.5 mA or 2 mA), duration (20 minutes or 30 minutes), and number of sessions (2, 4, 6, 8, or 10) on tinnitus suppression There are several open questions: how many sessions of tDCS are needed for optimal results? What should the washout period be between the tDCS sessions? What would be the outcome of head-to-head comparisons of multiple sessions of tDCS? The current trial was designed with the aim to optimize tDCS of DLPFC by investigating the impact of current intensity (1.5 mA or 2 mA), duration (20 minutes or 30 minutes), and number of sessions (2, 4, 6, 8, or 10) on tinnitus suppression
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