The intensity of transspinal direct current stimulation affects the excitability of the corticospinal system

BACKGROUND: Transspinal direct current stimulation (tsDCS) affects the corticospinal system (CSS), one of the central human systems associated with controlling precise voluntary movements. It is known, that the stimulation effects are very sensitive to montage and protocols of applied stimulation, because it can involve different neuronal mechanisms. AIM: This study aimed to estimate the parameters of anodal tsDCS applied at the level of the cervical enlargement of the spinal cord (C7-Th1 segments) on the excitability of the CSS and the correction of motor skills in healthy people. METHODS: The study involved 81 healthy adults aged 21.19 3.2 years. The effect of tsDCS was assessed using motor evoked potentials (MEP) from the first dorsal interosseous (FDI) muscle by transcranial magnetic stimulation in the primary motor cortex before stimulation, immediately after stimulation, and after 15 minutes. RESULTS: Our results showed that the application of 11-minute anodal tsDCS at the level of the cervical spine C7-Th1 with a current of 1.5 mA affects the FDI muscle, initially reducing the amplitude of TMS-induced MEP immediately after stimulation. The amplitude of the MEP increases after 15 minutes of stimulation. tsDCS with intensity 2,5 mA does not affect the MEP's amplitude change. Similarly, we found no difference in the effect of 1.5 mA stimulation on the correction of motor skills in healthy adults at 9-HPT and SRT, as with 2.5 mA. CONCLUSION: These results add information about optimally appropriate stimulation current intensities to induce CSS excitability and the ability of tsDCS to influence motor skills in healthy adults.