Several studies emphasized the potential of single and multiple transcranial random noise stimulation sessions to interfere with auditory cortical activity and to reduce tinnitus loudness. It was the objective of the present study to evaluate the use of high-frequency tRNS in a one-arm pilot study in patients with chronic tinnitus.
Therefore, 30 patients received 10 sessions of high frequency tRNS over the bilateral temporal cortex. All patients had received rTMS treatment for their tinnitus at least 3 months before tRNS. Primary outcome was treatment response. Transcranial random noise stimulation (tRNS) is a non-invasive brain stimulation method using varying alternating currents to interfere with oscillatory brain activity.
The enhancement neuronal
Technically, tRNS represents a special form of transcranial alternating current stimulation (tACS) with the current alternating at random normally distributed frequencies. Even short-term tRNS of 4 minutes was show to modulate the blood oxygen level dependent (BOLD) signal in the human motor cortex. Its putative mechanism of action is the enhancement of neuronal noise and the decrease of hypersynchronicity.
It was hypothesize that the main mechanism of tRNS action was base on repeat subthreshold stimulations; which might prevent homeostasis of the system and potentiate task relate neural activity. In patients with tinnitus; the effects of single sessions of tDCS, tACS and low-frequency tRNS of the auditory cortex were compare regarding tinnitus; so loudness and the tinnitus relate distress after stimulation of the auditory cortex.
A direct comparison of three non-invasive stimulation methods apply to the bilateral auditory cortex in 111 tinnitus patients demonstrated that the transient suppressive effect on tinnitus loudness and tinnitus relate distress was larger after tRNS compare to tDCS and tACS. Both tDCS and tACS induce small and non-significant effects on tinnitus perceptions; suggesting lf-tRNS as a superior brain stimulation method for tinnitus suppression.
Treatment of chronic tinnitus
Treatment of chronic tinnitus with hf-tRNS is easily applicable; show tolerable side effects; but result in temporal increases in tinnitus loudness in 20% of the cases leading to two drop outs. One advantage over rTMS is that tRNS is not with pulse local aversive sensations inherent to TMS stimulation. During tRNS patients report either constant slight tingling or no local sensations at all.
As tRNS provides a balance current stimulation it is consider even safer than tDCS; which induces a polarizing stimulation possibly leading to skin lesions under certain conditions. Accordingly, no erythema or burning skin lesion were observe in our study. In our clinical cohort no significant effects on cognitive functioning; which were detect assuming tRNS of the bilateral temporal cortex as a safe procedure even if apply on a repetitive basis of 10 sessions.
Taken together, our pilot study provides evidence for the feasibility of high frequency tRNS; which in the treatment of chronic tinnitus and demonstrate an identical low response rate compare to transcranial magnetic stimulation in a study cohort; which was treat almost two years after the first neurostimulation treatment attempt with rTMS. In sum, the trial was negative as no secondary outcome measure was significant including TQ. As the subgroup of patients who respond to hf-tRNS differed from rTMS responders; the results advocate to further focus on individualized treatment approaches.