Occlusion of bidirectional plasticity by preceding low-frequency stimulation in the human motor cortex.
OBJECTIVE
Low-frequency stimulation, which does not induce long-term potentiation (LTP) or long-term potentiation (LTD) by itself, suppresses consecutive LTP or LTD induction in vitro. We tested whether a similar interaction occurs in the human motor cortex.


METHODS
LTP- or LTD-like plasticity was induced using paired associative stimulation (PAS) with 25 and 10 ms interstimulus interval and conditioned by suprathreshold repetitive transcranial magnetic stimulation (rTMS) at a frequency of 0.1Hz.


RESULTS
RTMS completely abolished the significant increase of motor-evoked potential (MEP) amplitudes after PAS(25 ms) (PAS(25 ms) only: 1.05+/-0.14 to 1.76+/-0.66 mV, p=0.001; rTMS+PAS(25 ms): 1.08+/-0.18 to 1.02+/-0.44 mV, n.s.) and also abolished the significant decrease of MEP amplitudes after PAS(10 ms) (PAS(10 ms) only: 1.00+/-0.14 to 0.73+/-0.32 mV; rTMS+PAS(10 ms): 1.15+/-0.35 to 1.25+/-0.43 mV, p=0.006). RTMS alone did not significantly alter MEP amplitudes but increased SICI and LICI.


CONCLUSIONS
Low frequency stimulation increases intracortical inhibition and occludes LTP- and LTD-like plasticity in the human motor cortex.


CONCLUSIONS
This finding supports the concept that metaplasticity in the human motor cortex follows similar rules as metaplasticity in in vitro experiments.
Delvendahl
Igor
I
Division of Neuropaediatrics and Muscular Disorders, Department of Paediatrics and Adolescent Medicine, University Hospital Freiburg, Freiburg, Germany.
Jung
Nikolai H
NH
Mainberger
Florian
F
Kuhnke
Nicola G
NG
Cronjaeger
Matthias
M
Mall
Volker
V
D000328:Adult; D001703:Biophysics; D013181:Cortical Spreading Depression / Q000502:physiology*; D004558:Electric Stimulation / Q000379:methods; D004576:Electromyography / Q000379:methods; D019054:Evoked Potentials, Motor / Q000502:physiology*; D005260:Female; D006801:Humans; D008297:Male; D008475:Median Nerve / Q000502:physiology; D009044:Motor Cortex / Q000502:physiology*; D015999:Multivariate Analysis; D018482:Muscle, Skeletal / Q000294:innervation; D009433:Neural Inhibition / Q000502:physiology*; D009473:Neuronal Plasticity / Q000502:physiology*; D011930:Reaction Time / Q000502:physiology; D013997:Time Factors; D050781:Transcranial Magnetic Stimulation / Q000379:methods; D055815:Young Adult