A comparative study of the effects of repetitive paired transcranial magnetic stimulation on motor cortical excitability.
OBJECTIVE
Various methods of application of repetitive transcranial magnetic stimulation (TMS) have been evaluated for their potential capacity to alter motor cortical excitability. Initial research suggests that the repetitive application of paired TMS pulses (repetitive paired pulse TMS (rppTMS)) may have greater effects on cortical excitability, perhaps through the facilitation of I-wave interaction. We aimed to compare the post-train effects of 15 min trains of rppTMS to investigate the potential therapeutic application of this technique as well as to compare it to a standard high frequency repetitive TMS paradigm.


METHODS
Ten normal subjects received three 15 min sessions of rppTMS, 5 Hz high frequency rTMS and sham TMS in randomised order. rppTMS consisted of a single train of 180 pulse pairs (0.2 Hz, 1.5 ms inter-stimulus interval, supra-threshold intensity) administered over 15 min. The rTMS condition involved 750 pulses provided in 5s 5 Hz trains with a 25s inter-train interval at 90% of the RMT. Motor evoked potential size and cortical silent period duration were assessed before and after each session.


RESULTS
There were no significant changes in cortical excitability produced by any of the stimulation conditions. Five hertz rTMS produced an increase in cortical silent period duration (p=0.004) which was not affected by rppTMS.


CONCLUSIONS
Fifteen minutes trains of 1.5ms rppTMS do not substantially increase post train cortical excitability. Repetitive brief trains of 5Hz rTMS also do not alter excitability but appear to effect cortical inhibition.
Fitzgerald
Paul B
PB
Alfred Psychiatry Research Centre, The Alfred and Monash University School of Psychiatry, Psychology and Psychological Medicine, Commercial Road, Melbourne, Victoria 3004, Australia. paul.fitzgerald@med.monash.edu.au
Fountain
Sarah
S
Hoy
Kate
K
Maller
Jerome
J
Enticott
Peter
P
Laycock
Robin
R
Upton
Daniel
D
Daskalakis
Zafiris J
ZJ
D000328:Adult; D004594:Electrophysiology / Q000295:instrumentation / Q000379:methods*; D019054:Evoked Potentials, Motor / Q000502:physiology; D005260:Female; D006801:Humans; D008297:Male; D009044:Motor Cortex / Q000502:physiology*; D009474:Neurons / Q000502:physiology; D009482:Neurophysiology / Q000295:instrumentation / Q000379:methods*; D011712:Pyramidal Tracts / Q000502:physiology; D011930:Reaction Time / Q000502:physiology; D013997:Time Factors; D050781:Transcranial Magnetic Stimulation / Q000379:methods*