Long-lasting increase in corticospinal excitability after 1800 pulses of subthreshold 5 Hz repetitive TMS to the primary motor cortex.
OBJECTIVE
To study the after effects of high-frequency repetitive transcranial magnetic stimulation (rTMS) over the primary motor cortex (M1) on corticospinal excitability.


METHODS
Eight healthy volunteers received either 150 or 1800 stimuli of 5 Hz rTMS on two separate days in a counterbalanced order. rTMS was given over the 'motor hot spot' of the right first dorsal interosseus (FDI) muscle using an intensity of 90% of resting motor threshold (referred to as subthreshold rTMS). We evaluated the amplitude of the motor-evoked potential (MEP), short-latency intracortical inhibition (SICI), short-latency intracortical facilitation (SICF), and cortical silent period (CSP) before and for about 30 min after rTMS. MEPs were recorded from the right FDI muscle and abductor digiti minimi (ADM) muscle.


RESULTS
1800 stimuli induced an increase in MEP amplitude in the relaxed FDI muscle, but not in the relaxed ADM muscle. This facilitatory after effect was stable for at least 30 min. Prolonged 5 Hz rTMS had no effect on the relative magnitude of SICI and SICF. 150 stimuli caused no lasting modulation of MEP amplitudes in either muscle. In a subgroup of 5 subjects, 900 conditioning stimuli caused only a short-lived MEP facilitation. 5 Hz rTMS did not modify the duration of the CSP during tonic contraction.


CONCLUSIONS
A single session of subthreshold 5 Hz rTMS to the M1 can induce a long-lasting and muscle-specific increase in resting corticospinal excitability. However, a sufficient number of conditioning stimuli is necessary to produce persistent corticospinal facilitation.
Peinemann
Alexander
A
Department of Neurology, Technische Universität München, Möhlstrasse 28, D-81675 Munich, Germany.
Reimer
Bibiana
B
Löer
Christian
C
Quartarone
Angelo
A
Münchau
Alexander
A
Conrad
Bastian
B
Siebner
Hartwig Roman
HR
D000328:Adult; D003213:Conditioning, Psychological; D004056:Differential Threshold; D004558:Electric Stimulation / Q000379:methods*; D004576:Electromyography; D019054:Evoked Potentials, Motor; D005260:Female; D006225:Hand / Q000502:physiology; D006801:Humans; D008280:Magnetics; D008297:Male; D009044:Motor Cortex / Q000502:physiology*; D018482:Muscle, Skeletal / Q000502:physiology; D009433:Neural Inhibition; D009473:Neuronal Plasticity; D011712:Pyramidal Tracts / Q000502:physiology*; D011930:Reaction Time; D013997:Time Factors