Does Anodal Transcranial Direct Current Stimulation Over the Primary Motor Cortex Really Enhance Motor Sequence...

Area of Science:

• Neuroscience
• Neuromodulation
• Motor Learning

Background:

• Transcranial direct current stimulation (tDCS) is thought to modulate brain activity by directly polarizing neurons.
• Recent evidence suggests tDCS may indirectly influence cortical excitability via peripheral nerve stimulation due to strong scalp electric fields.
• This study investigated whether tDCS effects on motor sequence learning (MSL) are due to cortical polarization or peripheral nerve stimulation.

Purpose of the Study:

• To replicate findings on anodal tDCS enhancing MSL.
• To differentiate between cortical and peripheral nerve stimulation mechanisms in tDCS-induced MSL.
• To assess the impact of tDCS on MSL in a controlled experimental setting.

Main Methods:

• A double-blind, preregistered study with 99 adults.
• Anodal tDCS (1 mA) applied over the primary motor cortex (M1) during a 3-session serial reaction time task (SRTT).
• Control conditions included sham stimulation and a peripheral nerve block using BL10 gel to isolate effects.

Main Results:

• Significant improvements in MSL were observed within and across sessions in all conditions (p < .0001).
• No significant differences in MSL were found between the tDCS, sham, and peripheral nerve block conditions (p = .94).

Conclusions:

• The study could not confirm the primary research question due to the lack of significant tDCS effects on MSL.
• Findings suggest that tDCS-induced motor effects may be smaller than previously reported.
• The results contribute to a growing body of evidence questioning the reliability of tDCS as a neuromodulation technique.