Transcutaneous spinal direct current stimulation for motor recovery: a review of mechanistic insights and clinical efficacy

Abstract

Transcutaneous spinal direct current stimulation (tsDCS) has emerged as a promising non-invasive neuromodulation technique for improving motor performance in both healthy individuals and those with cortico-spinal tract damage, including stroke and spinal cord injury. This comprehensive review synthesized evidence from animal models, healthy individuals, and clinical populations to elucidate the mechanisms and therapeutic potential of tsDCS. A literature search was performed across the PubMed, Scopus, and Web of Science databases from January 2014 to December 2024 using defined keyword combinations; studies were rigorously selected based on preset inclusion criteria, with data extracted and synthesized by two independent reviewers. These findings indicate that, depending upon the current flow, tsDCS enhances motor unit recruitment in the target muscle, modulates spinal reflex circuits, and improves corticospinal transmission mainly at the alpha-motoneuronal level, thereby facilitating neuroplasticity and motor function recovery. Notably, the combination of tsDCS with adjunctive therapies - such as robotic gait training and neuromuscular electrical stimulation – appears to augment clinical outcomes further. However, the review also shows the significant heterogeneity in stimulation protocols, with variations in intensity, duration, and polarity/electrode montage potentially impeding direct clinical translation. As a result, standardized methodologies and large-scale, rigorously designed trials are urgently needed to define optimal stimulation parameters and establish efficacy across diverse patient populations. Overall, tsDCS represents a promising approach in neurorehabilitation, with future research needed to refine stimulation parameters and explore its broader clinical applications.