Effect of Voluntary Contraction in Motor Evoked Potential and Silent Period by Transcranial Magnetic Stimulation

OBJECTIVE: To determine the effects of the voluntary contraction of muscles and magnetic stimulation intensity on the motor evoked potential (MEP) and the silent period (SP). METHOD: We studied MEPs and SPs in opponens pollicis muscle in 30 healthy adults (male: 16, female: 14) while varying the amount of the voluntary contraction and the stimulation intensity. We analyzed MEPs and SPs in relation to sex, recording site, opposition power and height. RESULTS: 1) During the contraction, the latencies of MEP were significantly shorter than during the relaxation. 2) The amplitudes of MEP reached plateau at 30% of maximal voluntary contraction and increased with increment of stimulation intensity without limitation. The amplitudes of MEP of right hand were bigger than left hand. There were no significant differences according to sex and recording site. 3) The durations of SP were directly proportional to the degrees of voluntary contraction and the stimulation intensity. CONCLUSION: Transcranial magnetic stimulation should be performed under the same voluntary contraction and magnetic stimulation intensity.

Motor Unit Numbers Estimation in Abductor Pollicis Brevis Muscle of Normal Adult

OBJECTIVE: To estimate the motor unit numbers in normal adult hand muscles using manual incremental technique and F-wave technique. METHOD: We estimated the motor unit numbers in abductor pollicis brevis muscles of twenty normal adults. In manual incremental technique, we estimated the motor unit numbers using motor unit count program setted in electrodiagnostic equipment (Dantec, Keypoint). In F-wave technique, we estimated the motor unit numbers dividing maximal M-potential amplitude by mean amplitude of surface motor unit action potential. RESULTS: There was no significant difference of motor unit numbers between right and left abductor pollicis brevis in both manual incremental and F-wave technique. Motor unit numbers using F-wave technique were significantly greater than motor unit numbers using manual incremental technique. CONCLUSION: The difference of motor unit numbers using manual incremental technique and F-wave technique was considered as a difference of functional electrical stimulation. F-wave technique was more physiologic and functional method of motor unit numbers estimation than manual incremental technique.

Comparison of Motor Evoked Potential Using Round Coil with That Using Butterfly Coil

OBJECTIVE: To compare motor evoked potential stimulated by round coil with that stimulated by butterfly coil. METHOD: Thirty control subjects were studied using magnetic stimulation by round coil and butterfly coil. Stimulation sites were cortex, cervical spine and lumbar spine. Recording electrodes were located on biceps brachii, abductor digiti minimi and tibialis anterior muscles. RESULTS: There were no significant differences between latencies of motor evoked potentials using round coil and those using butterfly coil in all tested muscles. In all muscles, amplitudes were significantly higher in stimulation with round coil than with butterfly coil. Above results were shown in both cortical and spinal motor evoked potentials. There were significant correlations between latencies of motor evoked potentials, heights, and arm lengths. CONCLUSION: We can record motor evoked potentials more easily with round coil than butterfly coil.

The Effects of Jendrassik Maneuver on the T-reflex and the H-reflex of Soleus Muscle

OBJECTIVE: To investigate the effects of Jendrassik maneuver on latency and amplitude of the T-reflex and H-reflex of the soleus muscle in normal adults. METHOD: The T-reflex and H-reflex tests were performed on sixty normal adults with standardized technique using the soleus muscle. The shortest latency and the largest peak-to-peak amplitude were chosen for representative values. RESULTS: The results were as follows: 1) There was a significant difference in latency of the T-reflex between with and without Jendrassik maneuver. 2) The increment ratio of the amplitude with Jendrassik maneuver was 88% in the T-reflex and 18% in the H-reflex. There were a significant difference in the amplitude of both reflexes between with and without Jendrassik maneuver. 3) A high correlation was present between the latency of H- & T-reflex and the length. CONCLUSION: According to these results, we suggest that Jendrassik maneuver primarily increases the sensitivity of muscle spindles and decreases the presynaptic inhibition of the Ia terminals at cortical, subcortical and spinal levels. Jendrassik maneuver can be a useful tool in cases of clinically decreased or absent deep tendon reflex.