The Effect of Sub-threshold 1 Hz and 20 Hz Repetitive Transcranial Magnetic Stimulation on Corticospinal Excitability

ABSTRACT

OBJECTIVE: This explored whether the effects of Repetitive Transcranial Magnetic Stimulation (rTMS) on corticospinal excitability are dependent on the stimulation frequency. METHOD: Ten subjects were investigated using either 20 Hz or 1 Hz rTMS. To reduce inter-individual variability, we explored same subject in one week interval with different frequency. TMS was conducted with intensity of 90% of motor threshold. The effect of rTMS with EMG amplitude evoked in First Dorsal Interossei by TMS. Test motor evoked potentials were evaluated with intensity of 110% of motor threshold before rTMS, during the interval and immediately, 5 minutes, 20 minutes after the end of train. RESULTS: The analysis showed a significant decrease of cortical excitability after 1 Hz rTMS and an increase after 20 Hz rTMS. In low-frequency, Motor Evoked Potential (MEP) amplitude decreased quickly after initial 300 pulses stimulation. In high-frequency, there were some variation of individual MEP in the response to rTMS. The changes of MEP amplitude after 1200 stimulation continued until 20 minutes. CONCLUSION: These results provided basic evidence of rTMS for modulation of cortical excitability and could be further applied in patients group.