[The study of the central motor conduction time to the leg: normal findings and methodologic observations]

Central motor conduction time (CMCT) is calculated by subtracting latencies from each other measured to a target muscle after transcranial brain stimulation and after stimulation of lumbar spinal nerve roots. Transcranial magnetoelectrical stimulation of the motor cortex has proved to be the most useful method. However this is not true for transcutaneous stimulation of lumbar roots. In healthy subjects electrical root stimuli given at T12/L1 produced compound muscle responses in Tibialis anterior muscles in all 18 trials. However, magnetoelectrical stimulation (100% stimulus strength) evoked responses in only 8 (Novametrix) and 12 out of 18 trials (Cadwell). Stimulation with the Digitimer D190 was less effective. Additionally compound responses after electrical root excitation were more consistent and they had a higher amplitude compared with magnetoelectrical stimulation. Regarding to these results electrical lumbar root stimulation is thought to be the advantageous method despite it is slightly more uncomfortable. Therefore normal results of CMCT to Tibialis anterior (shown in Table 1) are measured after magnetoelectrical transcranial (Digitimer D190) and transcutaneous electrical stimulation of spinal nerve roots. If the peripheral motor conduction is delayed normal values have to be adapted since CMCT is thought to involve a proximal anterior root segment. An intraspinal motor conduction time can be calculated from CMCT to upper and lower extremities.