The Combination of Random Noise and Transspinal Direct Current Stimulation Affects the Corticospinal System Excitability

Transcranial random noise stimulation (tRNS) is a type of transcranial electrical stimulation. tRNS at the primary motor cortex affects corticospinal system (CSS) excitability. We assume that applying analogous protocols at the spinal cord level could similarly influence on CSS excitability, enabling a comparison of stimulation outcomes. This research aims to scrutinize the impact of combining random noise with transspinal direct current stimulation (tsDRNCS) at the level of cervical enlargement of the spinal cord (C7-Th1 segments) on CSS excitability, and to compare this data with previously obtained results from anodal transspinal direct current stimulation (tsDCS) at 1.5 mA. The effect of tsDRNCS was estimated by motor-evoked potentials (MEP) of the first dorsal interosseous (FDI) muscle induced by transcranial magnetic stimulation (TMS) in the primary motor cortex. The study involved 13 healthy adults aged 20,97 ± 2,85 years. The application of 11-minutes tsDRNCS had the effect of changing CSS excitability, as reflected in changes in MEP amplitudes of the FDI muscle. Initially, the amplitude of the MEP elicited by TMS increased immediately after stimulation, but with 15 minutes delay, the MEP amplitude decreased, which was validated through statistical analysis. Moreover, no significant difference in the effects was observed compared with earlier data obtained from anodal tsDCS at 1.5mA and sham tsDCS. However, increased CSS excitability following tsDRNCS tended to increase immediately after stimulation.