Method: MEPs induced by cortical stimulation were obtained at both thenar muscles in 28 post-stroke patients. Motor cortex was stimulated with 110% and 130% intensity of threshold during rest, minimal and moderate voluntary muscle contraction. We analyzed the MEP amplitude or area in 130% threshold intensity at rest (Rmax) and on moderate contraction (Fmax). The ratio of Fmax in both hemispheres (interhemispheric facilitation ratio, FR) and the ratio of Fmax to Rmax (facilitation index, FI) were also analyzed. Pinch strength, Brunnstrom stage, and Jebsen hand function test were included evaluating their motor functions.

Results: MEPs could not be evoked in cases whose Brunnstrom stage of hand was under 3. In response group, amplitude and area of Fmax of unaffected side were significantly larger than those of affected side (p＜0.05). FR showed good correlation with clinical findings evaluating motor functions (p＜0.05). In cases of FR ＞ 0.5, FI of unaffected side was significantly greater than that of affected side (p＜0.05).

Conclusion: We suggest to use FR and FI as useful parameters for evaluation of hand function in post-stroke patients. (J Korean Acad Rehab Med 2003; 27: 314-319)

Objective: To study the changes of magnetic evoked potentials by thinking of simple motion without actual muscle action of that motion.

Method: We use H-reflex to test the excitability of relevant pools of spinal motor neurons and Magnetic Evoked Potentials (MEPs) to study the core of brain motor activity. The H-reflex and MEPs were obtained in three different conditions. 1) non-facilitation (NF), that is, resting state without actual motion and without thinking of that motion. 2) volitional-faciliation (VF), with actual motion which is usual manner of facilitation of MEPs. 3) thinking-facilitation (TF), without actual motion but with imaginary thinking of that motion. We evaluate the thresholds, amplitudes and latencies of H-reflex and MEPs in each three condition.

Results: Comparing with the parameters in NF condition as a baseline, there were no significant changes in any parameters of H-reflex in TF condition, but there were significant changes in threshold and amplitude of H-reflex in VF. On the while there were significant changes both in VF and TF of MEPs. The amount of facilitation of MEPs were greater in VF than in TF; the amount threshold decrement, amplitude increment and latency decrement of MEPs were greater in VF than in TF.

Conclusion: Thinking of simple motion without actual muscle action of that motion could facilitate the MEPs, and this facilitation is induced by increasing activity of brain motor cortex not by that of spinal cord level.

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.

The study of blink reflexes was carried out to demonstrate the correlations, if there were, between the stage of diffuse axonal injury(DAI) and the abnormality of blink reflexes. The blink reflex was recorded in 20 healthy adult subjects and 22 patients with DAI who were classified according to Adams' classification(DAI I; 7, DAI II; 9 and DAI III; 6). The latencies and amplitudes of R1 and R2 in patients with DAI were compared with those of healthy subjects.

The results were as follows; 1) In 20 subjects of patient group, the latencies of R1 were all within a normal range. In 2 subjects, the difference in latencies between the two sides was above 1.4 msec. 2) In 15 subjects, R2 was absent or delayed, and reduced in the size of amplitude in all. Nine were affected bilaterally, and 4 were unilaterally. 3) Seventy one percent of patients in each stage represented abnormal findings. 4) There were no correlations between the DAI stage and the blink reflex.

This study demonstrated that the polysynaptic R2 was more profoundly suppressed than the oligosynaptic R1 in a diffuse axonal injury because of a loss or decrease of suprapontine facillitation, which influenced the trigeminal spinal complex and the interneuron of lateral reticular formation.