Increasing human leg motor cortex excitability by transcranial high frequency random noise stimulation

Area of Science:

• Neuroscience
• Motor Control
• Neuromodulation

Background:

• Transcranial random noise stimulation (tRNS) is known to increase excitability in the hand area of the primary motor cortex (M1).
• The efficacy of tRNS on the leg motor cortex remains less understood compared to transcranial direct current stimulation (tDCS).

Purpose of the Study:

• To compare the effectiveness of tRNS and tDCS in modulating the excitability of the leg motor cortex.
• To investigate the duration and magnitude of cortical excitability changes induced by these non-invasive brain stimulation techniques.

Main Methods:

• Ten healthy subjects participated in separate experimental sessions.
• Stimulation protocols included anodal tDCS, cathodal tDCS, tRNS, and sham stimulation, each lasting 10 minutes at 2 mA intensity.
• Motor cortical excitability was assessed using motor evoked potentials (MEPs) measured via single-pulse transcranial magnetic stimulation (TMS).

Main Results:

• Both tRNS and anodal tDCS significantly increased MEP amplitude, indicating enhanced motor cortex excitability.
• Anodal tDCS resulted in a sustained increase in corticospinal excitability for up to 60 minutes post-stimulation.
• tRNS produced an immediate effect lasting approximately 40 minutes, while cathodal tDCS did not yield statistically significant changes in MEP amplitude.

Conclusions:

• The leg motor cortex, despite its deeper cortical location, is responsive to weak transcranial electrical stimulation.
• Anodal tDCS and tRNS demonstrate comparable efficacy in modulating leg motor cortex excitability.
• The findings suggest potential therapeutic applications for both tDCS and tRNS in conditions affecting the leg motor system.