Effects of transcranial random noise stimulation timing on corticospinal excitability and motor function

Although transcranial random noise stimulation (tRNS) to the primary motor cortex (M1) increases corticospinal excitability and improves motor function, the effects of tRNS timing have not been clarified when combined with motor training. The purpose of this study was to clarify the effects of different tRNS timing on corticospinal excitability and motor function. We applied tRNS to the left M1 using a frequency of 0.1-640 Hz for 10 min to 15 healthy subjects. Subjects performed visuomotor tracking tasks with right hand for 10 min and participated in the following four conditions based on the timing of tRNS: (1) before condition, tRNS was performed before motor training; (2) during condition, tRNS was performed during motor training; (3) after condition, tRNS was performed after motor training; and (4) sham condition, the control group. Motor evoked potential (MEP) amplitudes were recorded from the right first dorsal interosseous muscle using transcranial magnetic stimulation. MEP amplitudes were assessed by baseline followed by three sessions at 10 min intervals. The motor function was assessed before and after tRNS and motor training. The MEP amplitude increased after tRNS in the before and during conditions but not in the after condition. Motor function after motor training improved in all conditions, but there were no significant differences between these conditions. The present study revealed that the timing of tRNS affects corticospinal excitability but not motor learning.

Automated summary

The study reveals that the timing of tRNS affects corticospinal excitability but does not have an impact on motor learning. Differences in corticospinal excitability were observed after motor training with tRNS applied at different timings, while there were no significant differences in motor function improvement between the conditions.