Optimization of facilitation related to threshold in transcranial magnetic stimulation.
OBJECTIVE
To attain the standardized procedure for optimal facilitation, we analyzed motor-evoked potential (MEP) responses to the degree of voluntary contraction and stimulus intensity.


METHODS
Fifteen normal subjects were included. MEPs were elicited at thenar muscles during rest and at gradual voluntary contraction (MVC), using 10, 30, and 50% of MVC. During rest and each contraction, the excitability threshold at rest (RET) and at contraction (CET) were determined. Consecutive stimuli were applied, with the intensity of ratio increments (110-150% of ET).


RESULTS
The RET showed a remarkable decrease after contraction. Shortening of latency reached a saturation level at 10% of MVC. Amplitude reached a saturation level at 30% of MVC with 62.7+/-8.5% of the maximum output, which is equal to 140% intensity of CET, and 110% of RET. The MEP amplitudes at rest and at 10% MVC were influenced by their ETs, but those measured above 30% of MVC were not related.


CONCLUSIONS
The procedure recommended for optimal facilitation is as follows: to achieve minimal latency of MEPs, a minimal contraction (10% of MVC) with RET intensity is sufficient and for maximal amplitude, a moderate contraction (30% of MVC) with 110% of RET intensity is adequate.
Han
T R
TR
Department of Rehabilitation Medicine, Seoul National University College of Medicine, 28 Yeongun-Dong, Chongro-Ku, Seoul 110-744, South Korea. tairyoon@snu.ac.kr
Kim
J H
JH
Lim
J Y
JY
D000328:Adult; D000368:Aged; D019054:Evoked Potentials, Motor / Q000502:physiology*; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D009044:Motor Cortex / Q000502:physiology*; D009119:Muscle Contraction / Q000502:physiology*; D018482:Muscle, Skeletal / Q000502:physiology; D013223:Statistics as Topic; D018709:Statistics, Nonparametric; D050781:Transcranial Magnetic Stimulation / Q000295:instrumentation