Comparison of the Effects of Transcranial Random Noise Stimulation and Transcranial Direct Current Stimulation on Motor Cortical Excitability

The objective of this study was to examine the effect of transcranial random noise stimulation (tRNS) with and without a direct current (DC) offset on motor cortical excitability and compare results to transcranial DC stimulation (tDCS).Fifteen healthy participants were tested in a within-subjects design. Motor-evoked potentials were measured before and up to 90 minutes after stimulation using transcranial magnetic stimulation. Five stimulation conditions were examined: sham, 1-mA tDCS, 2-mA tDCS, 2-mA tRNS (with no DC offset), and 2-mA tRNS + 1-mA DC offset.There were no significant differences between the stimulation conditions. An analysis of individual stimulation conditions found that there was a significant increase in motor-evoked potential amplitudes after 1-mA tDCS, 2-mA tDCS, and 2-mA tRNS + DC offset when compared with baseline. Sham and 2-mA tRNS did not result in changes in cortical excitability.Although differences between the stimulation conditions did not reach a statistical significance, the findings suggest that stimulation involving a DC (tDCS and tRNS + DC offset) but not solely tRNS is more likely to lead to increases in cortical excitability.