Bjoerndal, J. R. | bioRxiv Science

bioRxiv2026

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

neuroscience↗

bioRxiv2023

Hebbian priming of human spinal motor learning

Learning or relearning of motor skills requires plasticity in relevant neural circuits. Motor recovery following lesions to the corticospinal system can be augmented through neuromodulation techniques targeting the affected or compensatory neural circuits. By repeatedly pairing transcranial magnetic stimulation of the primary motor cortex (M1) and motoneuronal electrical stimulation (i.e., paired corticomotoneuronal stimulation, PCMS) timed to arrive at the corticomotoneuronal (CM) synapses in close temporal proximity, spike-timing-dependent bidirectional changes in CM transmission can be induced in humans (Taylor & Martin, 2009). PCMS-induced increases in CM transmission have been demonstrated to transiently improve motor control in patients with spinal cord injury (Bunday & Perez 2012), whereas effects on the malleability of neural circuits are entirely unexplored. We hypothesized that PCMS can prime mechanisms of subsequent motor learning exclusively when directed to the neural circuitry underpinning the motor behavior. In three experiments, we provide the first evidence ( Experiment I) and a double-blinded, sham-controlled replication ( Experiment II) that PCMS targeting the spinal CM synapses can prime subsequent learning of rapid finger movements relying on spinal neuroplasticity. Finally, we demonstrate that the effects of PCMS are circuit-specific and bidirectional. When PCMS was timed to arrive at a facilitatory interval in M1 but an inhibitory interval at the CM synapses subsequent learning was transiently impeded ( Experiment III). Taken together, our results provide proof-of-principle that non-invasively induced plasticity governed by Hebbian learning rules interacts with experience-dependent plasticity in the spinal cord with positive implications for motor learning. Our results offer a mechanistic rationale for priming sensorimotor training with individualized PCMS to enhance the effects of motor practice in neurorehabilitation. HighlightsO_LIPaired corticomotoneuronal stimulations (PCMS) promote ballistic motor learning and facilitate corticospinal excitability compared to rest and sham protocols. C_LIO_LIA double-blinded sham experiment replicates priming effects of PCMS on ballistic motor learning and demonstrates long-term benefits of combined PCMS and motor practice. C_LIO_LIThe facilitating effect of PCMS on ballistic motor learning is circuit-specific with superior effects on ballistic motor learning after facilitating PCMS compared to control protocols. C_LI

neuroscience↗