Spinal Reflex Evoked by Magnetic Stimulation

A noninvasive method of selective magnetic stimulation of the spinal roots is proposed. The basic idea is to concentrate induced eddy currents in a target region using a pair of opposing pulsed magnetic fields. A figure-eight coil is positioned outside the median of the back so that time-varying magnetic fields pass through the body in opposite directions around the target area. The spinal roots of human subjects and animals were stimulated magnetically. Each spine level was stimulated selectively, producing electromyographic (EMG) waves related to both the H-reflex and the M-waves. Experimental results indicate that the M-wave can be produced by currents flowing either in the rostral or caudal direction, whereas the H-reflex is generated by currents flowing in the caudal direction. The H-reflex elicited by magnetic stimulation will be useful for diagnosis of diseases of the neuro-muscular system.