Spinal Direct Current Stimulation Modulates Short Intracortical Inhibition

Area of Science:

• Neuroscience
• Neuromodulation
• Rehabilitation Medicine

Background:

• Transcutaneous spinal direct current stimulation (tsDCS) is an emerging, safe technique for modulating spinal cord excitability.
• Assessing intracortical excitability provides insights into the mechanisms of tsDCS.

Purpose of the Study:

• To evaluate the effects of tsDCS on intracortical excitability.
• To investigate changes in cortical silent period (cSP), paired-pulse short intracortical inhibition (SICI), and intracortical facilitation (ICF) following tsDCS.

Main Methods:

• Healthy subjects received anodal, cathodal, or sham tsDCS over the thoracic spinal cord.
• Changes in cSP, SICI (ISI = 3 ms), and ICF (ISI = 10 ms) were assessed at different time points.
• Motor-evoked potentials (MEPs) were recorded from the first dorsal interosseous (FDI) and tibialis anterior (TA) muscles.

Main Results:

• Cathodal tsDCS enhanced MEP amplitudes at a 3 ms interstimulus interval (ISI), while anodal tsDCS showed opposite effects.
• No significant changes in MEP amplitudes were observed at a 10 ms ISI.
• tsDCS did not significantly alter the duration of the cortical silent period (cSP).

Conclusions:

• tsDCS modulates the inhibitory GABA(A)ergic drive, as indicated by SICI changes.
• tsDCS does not interfere with cSP or ICF, suggesting targeted modulation of specific cortical pathways.
• tsDCS offers a promising approach for modulating spinal drive via non-spinal mechanisms and could be an early rehabilitation strategy for acute brain lesions or spinal conditions.