Suprathreshold 0.3 Hz repetitive TMS prolongs the cortical silent period: potential implications for therapeutic trials in epilepsy.
OBJECTIVE
To investigate the after-effects of 0.3 Hz repetitive transcranial magnetic stimulation (rTMS) on excitatory and inhibitory mechanisms at the primary motor cortex level, as tested by single-pulse TMS variables.


METHODS
In 9 healthy subjects, we studied a wide set of neurophysiological and behavioral variables from the first dorsal interosseous before (Baseline), immediately after (Post 1), and 90 min after (Post 2) the end of a 30 min long train of 0.3 Hz rTMS delivered at an intensity of 115% resting motor threshold (RMT). Variables under investigation were: maximal M wave, F wave, and peripheral silent period after ulnar nerve stimulation; RMT, amplitude and stimulus-response curve of the motor evoked potential (MEP), and cortical silent period (CSP) following TMS; finger-tapping speed.


RESULTS
The CSP was consistently lengthened at both Post 1 and Post 2 compared with Baseline. The other variables did not change significantly.


CONCLUSIONS
These findings suggest that suprathreshold 0.3 Hz rTMS produces a relatively long-lasting enhancement of the inhibitory mechanisms responsible for the CSP. These effects differ from those, previously reported, of 0.9-1 Hz rTMS, which reduces the excitability of the circuits underlying the MEP and does not affect the CSP. This provides rationale for sham-controlled trials aiming to assess the therapeutic potential of 0.3 Hz rTMS in epilepsy.
D000328:Adult; D000704:Analysis of Variance; D004056:Differential Threshold; D004558:Electric Stimulation / Q000379:methods*; D004574:Electromagnetic Fields; D004576:Electromyography; D004827:Epilepsy / Q000503:physiopathology / Q000628:therapy; D019054:Evoked Potentials, Motor / Q000502:physiology / Q000528:radiation effects*; D005260:Female; D005385:Fingers / Q000502:physiology; D006801:Humans; D008280:Magnetics; D008297:Male; D009044:Motor Cortex / Q000502:physiology / Q000528:radiation effects*; D009068:Movement / Q000502:physiology; D009433:Neural Inhibition; D011930:Reaction Time; D013997:Time Factors