A method to measure the distribution of latencies of motor evoked potentials in man.
OBJECTIVE
To measure the intra-individual distribution of the latencies of motor evoked potentials (MepL) using transcranial magnetic stimulation.


METHODS
We used the triple stimulation technique (TST) to quantify the proportion of excited spinal motor neurons supplying the abductor digiti minimi muscle in response to a maximal magnetic brain stimulus (Magistris et al., 1998). By systematically manipulating the TST delay, we could quantify the contribution of slow-conducting motor tract portions to the TST amplitude.


RESULTS
Our method allowed the establishment of a MepL distribution for each of the 29 examined healthy subjects. MepLs of 50% of the motor tract contributing to the motor evoked potential laid between the intra-individually minimal MepL (MepL(min)) and MepL(min)+4.9 ms (range 1.6-9.2). The individual MepL distributions showed two peaks in most subjects. The first peak appeared at a MepL that was 3.0 ms longer on average (range 0.7-6.0) than MepL(min); the second peak appeared at MepL(min)+8.1 ms on average (range 3.7-13.0).


CONCLUSIONS
Slow-conducting parts of the motor pathway contribute notably to the motor evoked potential. Our data suggest a bimodal distribution of central conduction times, which might possibly relate to different fibre types within the pyramidal tract.


CONCLUSIONS
We present a non-invasive method to assess slow-conducting parts of the human central motor tract.
Firmin
Lea
L
Department of Neurology, Inselspital, Bern University Hospital, and University of Bern, Switzerland.
Müller
Samuel
S
Rösler
Kai M
KM
D000200:Action Potentials / Q000502:physiology; D000328:Adult; D001369:Axons / Q000502:physiology; D019054:Evoked Potentials, Motor / Q000502:physiology*; D005260:Female; D006225:Hand / Q000294:innervation / Q000502:physiology; D006801:Humans; D008297:Male; D009044:Motor Cortex / Q000502:physiology*; D009046:Motor Neurons / Q000502:physiology; D018482:Muscle, Skeletal / Q000294:innervation / Q000502:physiology; D009413:Nerve Fibers, Myelinated / Q000502:physiology; D009431:Neural Conduction / Q000502:physiology*; D011712:Pyramidal Tracts / Q000502:physiology*; D011930:Reaction Time / Q000502:physiology*; D013997:Time Factors; D050781:Transcranial Magnetic Stimulation / Q000379:methods*; D055815:Young Adult