Review: Repetitive transcranial magnetic stimulation over the human primary motor cortex for modulating motor control and motor learning

Repetitive transcranial magnetic stimulation (rTMS) is a non-invasive technique that is capable of producing after-effects outlasting the stimulation for minutes to more than an hour. Varied paradigms and targets of the stimulation may produce different brain modulations corresponding to the changes of specific cortical plasticity. Conventional low-frequency rTMS depresses the cortical excitability, while high-frequency rTMS enhances the cortical excitability. More recently developed patterned rTMS paradigms do not follow the rule of frequency and produce inhibition and facilitation by adjusting the stimulus patterns. The ability of brain modulation makes rTMS an ideal tool to study the brain function in conscious humans. Here we focused our review on the effect of applying rTMS over the primary motor cortex (M1) on motor control and motor learning. We confirmed that rTMS modulated motor control and learning in line with its ability of changing cortical excitability. However, inconsistency and variability were among studies. Such inconsistency could be due to (1) different protocols and motor tasks in different studies, (2) poor efficiency of rTMS and (3) complicated neural network and indirect or remote effects induced by rTMS. The recent evolution of patterned rTMS, such as theta burst stimulation (TBS), might provide opportunities for in-depth understanding the effect of rTMS on motor performance and take a step closer to the potential use of rTMS in disease therapy.