Effect of slow rTMS of motor cortex on the excitability of the blink reflex: a study in healthy humans.

Objective: To evaluate the after-effects of low frequency, sub-threshold repetitive Transcranial Magnetic Stimulation (rTMS) of primary motor cortex, on the excitability of Blink Reflex (BR) in healthy subjects.

Methods: The BR recovery cycle was carried out in 10 healthy volunteers in basal conditions, immediately after rTMS (30s), 15 and 60min later. A paired electric supraorbital stimulus paradigm with inter-stimulus intervals (ISI) of 100-600-1000-1500ms was used. The "real" rTMS consisted of a 200 stimuli long train delivered at 1Hz and intensity 80% of rest Motor Threshold of the FDI muscle, using a focal coil applied over the primary motor cortex region. The basal BR recovery cycle was also compared with that obtained after a "sham" rTMS.

Results: The recovery of the R2 component of the BR was significantly suppressed 30s after rTMS. This effect was also observed at 15min, though of lower magnitude and only at long ISIs (1000-1500ms). No significant effect on R2 recovery was observed 60min after real rTMS as well as after sham rTMS.

Conclusions: rTMS of motor cortex modulates the excitability of BR through its action on cortical excitability and on the cortical facilitatory drive to the brainstem reflex pathways.

Significance: Slow (1Hz), sub-threshold rTMS of motor cortex determines a long-lasting reduction of excitability of BR.