Lasting influence of repetitive transcranial magnetic stimulation on intracortical excitability in human subjects.

We studied the effects of a train of 30 pulses of repetitive transcranial magnetic stimulation (rTMS) at frequencies of 5 and 15 Hz and at an intensity of 120% of resting motor threshold on human motor cortex excitability. Intracortical inhibition (ICI) and intracortical facilitation (ICF) after rTMS were tested by a conditioning-test designed paired-pulse paradigm. After 15 Hz rTMS, ICI was significantly reduced for 3.2 min, ICF was enhanced for 1.5 min, muscle evoked potentials from single TMS were increased in the first 30 s only. After 5 Hz rTMS ICI was significantly reduced in the first 32 s. We conclude that high-frequency suprathreshold rTMS transiently suppresses the activity of the intracortical inhibitory circuitry and, with a different time course, increases the excitability of the excitatory circuitry.