[Study of central motor pathways using cortical magnetic stimulation and spinal electrical stimulation: results in 20 normal subjects].

Evoked motor potentials can be elicited by magnetic cortical or electric spinal stimulations. The central conduction time (CCT) corresponds to the difference in latencies between the total conduction time (from cortex to muscle) and the peripheral conduction time (from spinal cord to muscle). CCT is the sum of the conduction time in the cortico-spinal fibers, of the spinal synaptic delay, and of the conduction time in the proximal part of the motor roots. CCT values (mean + standard deviation) were determined in 20 healthy subjects ranging from 21 to 56 years of age (mean 31.2). Results of magnetic cortical stimulation were compared to the results of electrical stimulation of the cortex. CCTs after magnetic cortical stimulation were longer than CCTs after electric cortical stimulation. This could be explained by the fact that electrical stimulation elicits a direct response in the cortico-spinal tract whereas magnetic cortical stimulation has indirect effects on the pyramidal cells of the motor cortex through excitatory interneurons. Compared with electrical stimulation, the magnetic stimulation has the great advantage of being painless and allows a safe evaluation of the central motor pathways in man.