Combined effects of concurrent motor imagery and high-frequency repetitive transcranial magnetic stimulation on human motor performance and corticospinal excitability

Introduction Combined therapeutic maneuvers may be more effective for improving motor dysfunction than single interventions. Although motor imagery (MI) and high-frequency repetitive transcranial magnetic stimulation (HF-rTMS) each may enhance cortical excitability and/or motor performance, whether simultaneous application yields superior effects remains unclear. This study aimed to investigate behavioral and neurophysiological changes induced by HF-rTMS applied concurrently with MI. Methods Participants underwent four modulation procedures in a crossover design: MI of a typing task alone, 5-Hz rTMS over the left primary motor cortex alone, concurrent MI with 5 Hz rTMS, and a control condition. Before and after each intervention, motor performance was evaluated by means of actual and imagined movement time, error rate, MI vividness, and surface electromyography of intrinsic and extrinsic hand muscles. Motor evoked potentials (MEPs) elicited by single-pulse TMS were also recorded at rest, during MI, and actual movement. Results No significant changes in motor or MI performance were observed following any intervention. Task-related corticospinal excitability, expressed relative to resting MEP amplitude (%rest), decreased during actual movement after concurrent MI with HF-rTMS compared with the control and MI-alone conditions. MEP persistence in the agonist muscle remained stable during HF-rTMS alone but declined during the latter half of the combined MI and HF-rTMS intervention. Discussion These findings suggest that concurrent MI and HF-rTMS modulated task-related corticospinal excitability without measurable changes in motor performance. This combination may enhance the modulation of motor cortical output in a task-dependent manner, supporting a neuromodulatory framework for optimizing motor cortical function.