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

BACKGROUND: Transspinal direct current stimulation (tsDCS) affects the corticospinal system, one of the central human systems associated with controlling precise voluntary movements. Stimulation effects are very sensitive to montage and protocols of applied stimulation because they can involve different neuronal mechanisms.

AIM: This study aimed to estimate the effects of parameters of anodal tsDCS applied at the level of the spinal cord (C7–Th1 segments) with cervical enlargement to determine the excitability of the corticospinal system and the correction of motor skills in healthy people.

METHODS: The study involved 81 healthy adults aged 21.19±3.20 years. The effect of tsDCS was assessed using motor-evoked potentials from the first dorsal interosseous (FDI) muscle by transcranial magnetic stimulation in the primary motor cortex before stimulation, immediately after stimulation, and after 15 min.

RESULTS: The application of 11-min anodal tsDCS at the C7–Th1 level with a current of 1.5 mA affects the FDI muscle, initially reducing the amplitude of transcranial magnetic stimulation induced motor-evoked potentials immediately after stimulation. The amplitude of the motor-evoked potentials increases after 15 min of stimulation. tsDCS with an intensity of 2.5 mA does not affect the change in the amplitude of motor-evoked potentials. Similarly, no difference was found in the effect of 1.5 mA stimulation on the correction of motor skills in healthy adults at the nine-hole peg test and the serial reaction time task as with 2.5 mA.

CONCLUSION: This study adds information about the optimally appropriate current intensities of stimulation to induce corticospinal system excitability and the ability of tsDCS to influence motor skills in healthy adults.