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Optimization of facilitation related to threshold in transcranial magnetic stimulation
1Department of Rehabilitation Medicine, Seoul National University College of Medicine, 28 Yeongun-Dong, Chongro-Ku, Seoul 110-744, South Korea. tairyoon@snu.ac.kr
Objectives:
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.