Cutaneous perception thresholds of electrical stimulation methods: comparison of tDCS and tRNS

Objective: Controlled blinded studies using transcranial electrical stimulation (tES) paradigms need a validated sham stimulation paradigm since an itching or tingling sensation on the skin surface under the electrode can be associated with current flow.

Methods: Here we investigated the skin perception thresholds of transcranial direct current stimulation (tDCS) and transcranial random noise stimulation (tRNS) for current intensities ranging from 200 to 2000μA and additional non-stimulation trials using a motor cortex-contralateral orbit montage in three different healthy subject groups: subjects naïve to tES methods, subjects with previous experience with these techniques and investigators, who use these methods in their research.

Results: Taking the whole sample into consideration the 50% perception threshold for both tDCS conditions was at 400μA while this threshold was at 1200μA in the case of tRNS. Anodal and cathodal tDCS are indistinguishable regarding sites of perception. Experienced investigators show a significantly higher anodal stimulation detection rate when compared to the naïve group, furthermore investigators performed significantly better than naïve subjects in non-stimulation discrimination.

Conclusions: tRNS has the advantage of higher cutaneous perception thresholds and lower response rates in when compared with tDCS. Further investigation in blinding methods (such as placebo itching) is warranted in order to improve sham control.

Significance: As tRNS has been shown to have similar aftereffects as anodal tDCS, this finding points to the application of tRNS as a possible alternative with a better blinding control.