Noninvasive neuromodulation of tinnitus with transcranial current stimulation techniques with insight into neurobiology and neuroimaging

Tinnitus is an auditory phantom percept in the absence of any objective physical sound source. Although advances have been made in its treatment, there is very low percent of patients that report an elimination of their tinnitus. A novel approach using noninv­asive neuromodulation has emerged as an inter­esting and promising modality for tinnitus relief. Our aim in this review is to investigate the efficacy and the specific parameters of some types of noninvasive neuromodulation using transcranial electrical stimulation (TES) namely transcranial direct current stimulation (tDCS), transcranial alternative current stimulation (tACS), transcranial random noise stimulation (tRNS). Then we will correlate the outcomes with the findings of the most newly neurobiol­ogic and neuroimaging researches.
Up to now, the optimal use of tDCS was to apply a current of 2 mA for 20 minute over both auditory cortex or dorsolateral prefrontal cortex. The results were somewhat good but still need more optimization. While there is no effects of tACS; tRNS is shown to have the more suppressive effects among the three types of TES, so it would be a promising therapeutic tool for modulating tinnitus. In addi­tion, recently many researches on tinnitus have shed light on the tinnitus generating network and it’s correlation to another functional brain networks. This article show how can the neuro­modulation be optimized by using these new concepts.
Although the different techniques introduced revealed promising results, further research is needed to better understand how they work and how the brain responds to neuro­modulation.