Submitted on July 6, 2007
Accepted on December 3, 2007
Preconditioning rTMS of premotor cortex can reduce but not enhance short-term facilitation of primary motor cortex
Antonio Suppa1, Matteo Bologna2, Francesca Gilio2, Cinzia Lorenzano2, John C. Rothwell3, and Alfredo Berardelli4*
1 Sobell Department of Motor Neuroscience and Movement Disorders, Institute of Neurology, University College London, London, United Kingdom; Neurological sciences and Neuromed Institute, Univeristy of Rome "La Sapienza", Rome, Italy
2 Neurological Sciences, University of Rome "La Sapienza", Rome, Italy
3 London, United Kingdom; Sobell Department of Motor Neuroscience and Movement Disorders, Institute of Neurology, University College London, London, United Kingdom
4 Neurological sciences and Neuromed Institute, Univeristy of Rome "La Sapienza", Rome, Italy
* To whom correspondence should be addressed. E-mail: alfredo.berardelli{at}uniroma1.it.
Introduction: Short trains of suprathreshold 5 Hz repetitive transcranial magnetic stimulation (rTMS) over primary motor cortex (M1) evoke motor potentials (MEPs) in hand muscles that progressively increase in amplitude via a mechanism that is thought to be similar to short term potentiation described in animal preparations. Long trains of subthreshold rTMS over dorsal premotor cortex (PMd) are known to affect the amplitude of single pulse MEPs evoked from M1. We tested whether PMd-rTMS affects short term facilitation in M1. We explored also the effect of PMd-rTMS on M1 responses evoked by single pulses TMS of different polarities.
Materials and Methods: We tested in 15 healthy subjects short term facilitation in left M1 (10 suprathreshold TMS pulses at 5 Hz) after applying rTMS to left PMd (1500 subthreshold pulses at 1 Hz and 5 Hz). In a sample of subjects we delivered single pulse TMS with different polarities, and paired-pulse TMS at short interval (SICI) after PMd-rTMS.
Results: Short term facilitation in M1 was reduced after applying 1 Hz to PMd, but was unaffected after 5 Hz PMd-rTMS. PMd 1Hz rTMS reduced the amplitude of MEPs evoked by monophasic PA or biphasic AP-PA but had little effect on MEPs by monophasic AP or biphasic PA-AP single pulse TMS. PMd-rTMS left SICI unchanged.
Discussion: 1 Hz PMd rTMS reduces short term facilitation in M1 induced by short 5 Hz trains. This effect is likely to be caused by reduced facilitation of I-wave inputs to corticospinal neurons.
