Effects of Single-Session High-Definition Transcranial Alternating Current Stimulation (HD-tACS) Combined with Robot-Assisted Hand Exercises on Corticospinal Excitability in Chronic Stroke

OBJECTIVE: This preliminary study investigated whether a single session of high-definition transcranial alternating current stimulation (HD-tACS) could improve corticospinal tract (CST) excitability compared with sham stimulation in healthy individuals and individuals with chronic stroke. DESIGN: Twelve healthy adults and 7 individuals with chronic stroke received active and sham HD-tACS over the primary motor cortex (M1) flexor digitorum superficialis (FDS) hotspot, ipsilesional in stroke subjects, for 30 minutes at 2mA and 21 Hz in a randomized crossover design. All subjects performed robot-assisted grasp-and-open hand exercises during active and sham stimulation. RESULTS: HD-tACS significantly increased FDS MEP amplitudes in the healthy group (15.3%). In the stroke group, FDS MEP amplitudes were increased by ∼22.3% after HD-tACS, but this change was not statistically significant. When MEP amplitudes were normalized as percentage change, HD-tACS significantly increased FDS MEP amplitudes in both groups compared with the sham condition. No significant extensor digitorum communis (EDC) modulation was observed in either group. CONCLUSION: HD-tACS combined with robot-assisted hand exercises may enhance CST excitability compared with robot-assisted hand exercises alone after a single session in both healthy and stroke subjects. However, larger studies are needed to confirm these findings.