CONDUCTION PATHWAYS OF MOTOR EVOKED-POTENTIALS FOLLOWING TRANSCRANIALMAGNETIC STIMULATION - A RODENT STUDY USING A FIGURE-8 COIL

We have examined the conduction pathways of motor evoked potentials (M EPs) elicited by transcranial magnetic stimulation, and their correlat ion with locomotor function in rats. MEPs were concomitantly recorded from the spinal cord (sMEPs) and the limb muscles (mMEPs) before and a fter various spinal tract ablations. Motor function was also examined using an inclined plane test, sMEPs were composed of four negative pea ks (N1-N4) and mMEPs of high-voltage, biphasic waves. Ventral funiculu s transection reduced the N1-N3 peaks and abolished mMEPs. Contrarily, dorsal funiculus transection including the pyramidal tract did not al ter these MEPs. Motor performance on an inclined plane was worse after ventral funiculus transection than after other transections. These fi ndings indicate that, in rats, the N1-N3 peaks of magnetic sMEPs condu ct ventral funiculus activity, and that magnetic mMEPs mainly reflect extrapyramidal activities and are correlated with locomotor function. (C) 1998 John Wiley & Sons, Inc.