Modulation of motor cortical excitability following rapid-rate transcranial magnetic stimulation.

OBJECTIVE: To investigate the effect of high frequency rTMS (25 Hz at 90-100% of resting motor threshold) on the excitability of the motor cortex of healthy human subjects. METHODS: Resting and active motor threshold, MEP recruitment curve (I/O curve), short interval intracortical inhibition (SICI) and facilitation (ICF), and the duration of the silent period (SP) were tested in the right first dorsal interosseous muscle (FDI) before and twice after the end of 1500 pulses in 16 normal young adult male volunteers. RESULTS: Twenty-five Hertz rTMS decreased motor thresholds, reduced the duration of the silent period and had a tendency to increase the slope of the I/O curve. Most of these effects lasted for the duration of the two post-testing sessions (at least 30 min) and had returned to normal by 2h. There were no significant effects on SICI/ICF. CONCLUSION: Twenty-five Hertz rTMS can produce a long lasting increase in cortical excitability in healthy subjects. SIGNIFICANCE: This method may prove useful for the study of normal human physiology and for therapeutic manipulation of brain plasticity.