Relationship between rTMS effects and MEP features before rTMS.

Repetitive transcranial magnetic stimulation (rTMS) is a promising method for use in the clinical field, as it can induce modulation of cortical excitability. Generally, rTMS inhibits the motor cortex when delivered at less than 1 Hz. However, it has been indicated that a facilitative effect is induced by 1 Hz rTMS, depending on the stimulation parameters and the individual. Therefore, the aim of this study was to investigate the features of the subject that could affect the 1 Hz rTMS effect when rTMS stimulus conditions change. First, motor evoked potentials (MEP) were measured under rTMS conditions with a variety of stimulus intensities and numbers of pulses. The MEP features before rTMS and the MEP modulation by the rTMS were then analyzed. Furthermore, correlations between the MEP features and the rTMS effect were investigated. It was found that the MEP amplitude and MEP onset before rTMS can influence the rTMS effect. Furthermore, negative correlations were found between these MEP features and the rTMS effect. MEPs with a small amplitude and early latency were little influenced by the inhibitive effect of 1 Hz rTMS, while MEPs with a large amplitude and late latency were readily affected by the inhibitive effect of 1 Hz rTMS. In this study, we focused on the MEP features before rTMS and identified the features of the subject that could influence the rTMS effect when the rTMS stimulus condition was changed.