Learning-Dependent Modulation of Corticospinal Excitability During TMS-Based Neurofeedback

Transcranial magnetic stimulation (TMS) provides a direct and reliable method for probing corticospinal excitability via motor-evoked potentials (MEPs). While neurofeedback (NF) approaches using EEG or fMRI have demonstrated learning-related neural modulation, it remains unclear whether repeated NF based on TMS-elicited MEPs can induce stable, learning-dependent changes in corticospinal output across multiple training sessions.

In this study, we investigated longitudinal changes in corticospinal excitability during TMS-based neurofeedback training. Twenty-two healthy adults were randomly assigned to a feedback (FB) group or a control (CON) group. Participants performed motor imagery-based mental practice over six training days (three sessions per week for two weeks). During each trial, a single TMS pulse was delivered over the left primary motor cortex at a fixed time, and MEPs were recorded from the right first dorsal interosseous muscle. In the FB group, trial-by-trial normalized MEP amplitudes were visually presented to participants as neurofeedback, whereas the CON group performed identical training without feedback.

Repeated-measures analysis revealed a significant interaction between group and training day for normalized MEP amplitudes. The FB group exhibited a consistent increase in corticospinal excitability from Day 2 through Day 6 relative to baseline, indicating the early acquisition and maintenance of neurophysiological modulation. In contrast, the CON group showed a significant increase in MEP amplitude on only a single training day, suggesting limited learning without feedback.

These findings demonstrate that TMS-based neurofeedback can facilitate learning-dependent modulation of corticospinal excitability across repeated sessions. The results highlight the potential of MEP-guided neurofeedback as a powerful experimental framework for studying motor system plasticity and neural self-regulation, and as a methodological foundation for future neurophysiological and brain-stimulation-based research.