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Journal of the Korean Academy of Rehabilitation Medicine 1998;22(6):1263-1270.
Optimization of Facilitation Threshold in Transcranial Magnetic Stimulation.
Han, Tai Ryoon , Kim, Jin Ho , Chung, Sun Gun , Lim, Jae Young
Department of Rehabilitation Medicine, Seoul National University College of Medicine.
자기자극에 의한 운동유발전위에서 흥분역치를 고려한 Facilitation의 최적화
한태륜, 김진호, 정선근, 임재영
서울대학교 의과대학 재활의학과교실
Abstract

Objectives: To analyze the motor evoked potential (MEP) responses to a degree of voluntary contraction and stimulus intensity and to suggest the standardized optimal stimulation for MEP responses.


Methods
MEPs induced by a cortical stimulation were elicited at the thenar muscles in 15 normal subjects during the rest and gradual voluntary contraction, using the 10% of maximal voluntary contraction (MVC), 30%, 50%, and MVC. During rest and during each contraction, excitability threshold at rest (RET) and at contraction (CET) were determined. Consecutive stimuli were applied, according to the intensity of ratio increment (110% to 150% of excitation threshold).


Results
The RET showed a remarkable decrease (57.1⁑8.2% → 47.4⁑8.7%) after the voluntary contraction (P<0.05). Shortening of latency reached the saturation level with 10% of MVC, irrespective of stimulus intensity. Amplitude reached a saturation level at 30% of MVC with 62.7% intensity of maximal output, which is equal to 140% intensity of its CET, and to 110% of RET. MEP amplitude at rest and at 10% of MVC were influenced by the excitation threshold (P<0.05), but those at above 30% of MVC were not related.


Conclusion
The procedure for optimal facilitation for the MEPs is as follows; for minimal latency of MEPs, minimal contraction (10% of MVC) with RET intensity is enough. For maximal amplitude of MEPs, moderate contraction (30% MVC) with 110% intensity of RET is adequate.

Key Words: Motor evoked potentials, Facilitation, Transcranial magnetic stimulation, Voluntary contraction


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