Transcranial Direct Current Stimulation enhances long-term retention after 5 days of lower-limb motor skill learning

Transcranial direct current stimulation (tDCS) holds the potential to affect behavior by modulating ongoing neural activity, and tDCS paired with hand motor practice can enhance motor learning. While augmenting the behavioral benefits of motor practice is relevant for neurorehabilitation following central and peripheral lesions to the motor system, as well as in sports, the short- and long-term effects of tDCS targeting the mesial motor cortex (M1-Leg) during lower-limb motor skill practice remain unexplored. We tested whether five days of anodal tDCS over M1-Leg during training of a sequential visuomotor tracking task improves within- and between-session learning and one-week retention. Participants were randomized to skill practice with active tDCS, skill practice with sham stimulation, or volume-matched non-skilled ankle movements with sham stimulation. Changes in corticospinal excitability accompanying skill and nonskill motor practice with real and sham tDCS, were assessed as motor evoked potential amplitudes recorded from the tibialis anterior muscle at rest. Compared to non-skill practice, motor skill practice yielded robust sequence-specific performance gains, which were transferred to the untrained leg and persisted for at least one week after practice ended. Concurrent tDCS did not increase learning within or between training sessions, but it did lead to improved one-week retention compared to sham stimulation. Corticospinal excitability did not increase after practice and was unaffected by tDCS. These findings suggest that combining lower-limb motor skill practice with tDCS over M1-Leg can strengthen retention of skill learning without measurable changes in resting corticospinal excitability. This is relevant for motor practice scheduling in neurorehabilitation. Key pointsO_LITranscranial direct current stimulation (tDCS) is a weak electrical brain stimulation that may boost learning when paired with motor practice; however, its effects during lower-limb skill training are not well known. C_LIO_LIWe tested whether stimulation over the leg area of the motor cortex during 5 days of ankle skill training improves learning, consolidation, and delayed retention. C_LIO_LIAnkle skill training produced clear sequence-specific improvements that transferred to the untrained leg and were still present 1 week later. C_LIO_LIStimulation did not increase short-term learning, but it did improve 1-week retention compared to sham stimulation. C_LIO_LICorticospinal excitability assessed based on motor evoked potentials elicited by transcranial magnetic stimulation did not change with motor training or stimulation, suggesting that the observed positive effect of tDCS on delayed retention may arise from other brain network processes relevant to long-term motor learning and memory. C_LI