The effect of transcranial random noise stimulation on corticospinal excitability and motor performance.

Although transcranial random noise stimulation (tRNS) over the primary motor cortex (M1) region can be used to enhance cortical excitability, it remains unclear whether tRNS over the M1 region improves motor performance. The present study aims to clarify the effect of tRNS on both corticospinal excitability and motor performance. We applied tRNS at the frequency range of 0.1-640 Hz over the left M1 for 10 min to 16 healthy adults. All subjects were tested in the following two interventions: (1) tRNS condition and (2) sham condition. Motor evoked potential (MEP) amplitudes were recorded from the right first dorsal interosseous muscle by transcranial magnetic stimulation. The motor performance was evaluated using a visuomotor tracking task by isometric abduction motion of the right index finger. MEP amplitudes and motor performance were measured before intervention, immediately after and 10 min after the intervention. The two interventions (tRNS and sham) were randomly performed separated by a break of at least 1 week. In the tRNS condition, MEP amplitudes were significantly increased immediately and 10 min after the intervention, while the motor performance was significantly improved 10 min after the intervention. The present study revealed that tRNS over the M1 region is effective for cortical excitability as well as for motor performance.